Machsupport Forum
General CNC Chat => Show"N"Tell ( Your Machines) => Topic started by: HimyKabibble on June 16, 2009, 04:27:58 PM
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I'm in the process of adding a toolchanger to my BP clone mill. First step is a power drawbar. Rather than use the very common impact wrench approach, I wanted something that would leave the collet in place, and simply pop out the tool. I will be using Tormach TTS toolholders. So, taking a page from the design of many VMCs, I've created a design that tensions the drawbar using a stack of Belleville washers. The drawbar is initially tensioned in the normal manner, by tightening with a wrench, to compress the Belleviille washers enough to create the desired drawbar tension (about 2000 pounds, as it turns out...). To release the tool, all that's required is to compress the Bellevilles a bit further, then push the drawbar down to pop the collet free of the taper, and the tool simply falls out. The trick is to provide a means of compressing the Bellevilles that does not place that 2000+ pound load on the spindle bearings. To accomplish that, a small arm is rotated in under the Bellevilles, to take the downward load.
Since, on my first attempt at this, I was largely shooting in the dark as far as the required forces, and some of the other side-effects of the design, I've found I need to make a few minor modifications to the design to get it working properly. But, the first attempt, shown in the below pictures, does, in fact, work pretty well. The biggest problem is I under-estimated the drawbar tension required, and the air cylinder in the pictures is not quite up to the task. A larger cylinder will be here in a day or two, which should do the job nicely. The other "gotcha" is that the long drawbar extension sticking up above the head "whips" at speed - not good. So, it will be surrounded by a cylindrical guide, rigidly attached to the spindle, that will rotate with the spindle and prevent any whipping.
The assembly is fastened to the head, by bolting an adaptor ring to the flange that retains the upper bearing outer race. The upper bearing inner race retainer is replace with the drawbar guide tube. The adaptor has two guide rods rigidly attached. The rest of the assembly "floats" on these guide rods. The guide rods have concentric springs on them such that the whole floating assembly is spring-loaded downward. To do a toolchange, the quill is run fully up, which causes the top of the drawbar to contact the plunger in the center top of the drawbar assembly. This compresses the springs, placing a downward force on the drawbar assembly. This is the force that is used to pop the collet free, and will probably be on the order of 100 pounds - hardly enough to harm the spindle bearings. A small air cylinder then flips an arm in under the flange that lsupports the bottom of the stack of Belleville washers on the drawbar. Once that arm is in position, the large air cylinder is activated, which compresses the Bellevilles between that arm, and the plunger. Since the whole assembly is floating on the guide rods, none of the Belleville force is transmitted to the spindle - only the initial downforce of the springs on the guide rods is transmitted to the spindle. Once the Bellevilles are compressed sufficiently (0.030-0.050"), the collet pops free of the taper, and the tool falls out. Once the new tool is installed, the air pressure is removed from both cylinders, and the collet is once again locked by the tension in the Bellevilles.
This is a totally bolt-on design, which requires absolutely no modifications whatsoever to the machine. Drawbar tension can be adjusted over a very wide range by simply changing the number and type of Belleville washers used, and, if necessary, the strength of the air cylinder. Collet-popping force is adjustable by adjusting the pre-load on the downforce springs. Initial position is set by simply adjusting the length of the link on the air cylinder. All very simple and flexible. Tool changes become almost instantaneous - literally less than a second to engage or disengage the drawbar.
For the toolchanger, I am taking a very simple route, since I only need a few tools - I will have a single-row rack of tools mounted to the T-slot along the front face of the table, holding perhaps 8-10 tools, or perhaps 4-6 tool racks mounted at either end of the table. The tool pick-and-place will be handled entirely by moving the machine, with no additional mechanism required. This does cost a small amount of useable table travel, but since I have a 49" table with 34" of travel, I am more than happy to lose a few inches of workspace in exchange for the huge increase in productivity I'll get from the toolchanger.
Regards,
Ray L.
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Looks good Ray. :)
Hood
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looks really neat .
Have you thought of just using a 4" bore pancake cylinder supported over the end of the factory drawbar?
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looks really neat .
Have you thought of just using a 4" bore pancake cylinder supported over the end of the factory drawbar?
Considered it, but it wouldn't get the job done. At 100 PSI, a 4" cylinder would be only about 1200#. I need at least twice that. Plus, it would have too much travel. I only need a total of about 0.100".
Regards,
Ray L.
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Ray LOOKS good. Here is something to consider. The piece that holds UP on the spring pack, the lower plate with the finger that slides under the pack. THis will be tricky to get the spindle in the exact position so the lever can slide under the pack AND still not have any play. ANY PLAY will cause the spindle bearings to load up as the pack is compressed. You might want to consider a push me pull me type of compressor arrangement that floats and as it is compressed both sides of the PACK are compressed at the same time. AND it puts zero load on the drawbar.
Another thought when building a drawbar is the machines always use a long 30deg angle tool holder that does NOT require any of the force of holding in the toolholder to be used to HOLD the bit as well. (;-)
Just a thought, (;-) TP
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Ray LOOKS good. Here is something to consider. The piece that holds UP on the spring pack, the lower plate with the finger that slides under the pack. THis will be tricky to get the spindle in the exact position so the lever can slide under the pack AND still not have any play. ANY PLAY will cause the spindle bearings to load up as the pack is compressed. You might want to consider a push me pull me type of compressor arrangement that floats and as it is compressed both sides of the PACK are compressed at the same time. AND it puts zero load on the drawbar.
Another thought when building a drawbar is the machines always use a long 30deg angle tool holder that does NOT require any of the force of holding in the toolholder to be used to HOLD the bit as well. (;-)
Just a thought, (;-) TP
Terry,
Not so. Initial position is not at all critical. It simply needs to move up enough that the drawbar contacts the plunger. At that point, the latch plate is guaranteed to be clear, so it can slide into position easily, as the whole assembly floats. There will be slack in there, by design. The initial movement of the plunger will lift the assembly further until the latch plate contacts the underside of the flange under the Belleville stack. It is impossible for any force to be transmitted to the spindle. Further movement of the plunger will then compress the Bellevilles. The only force that can be transmitted to the spindle is the initial downforce provided by the springs on the guide rods, which is strictly limited, and provided purely to pop the colet free of the taper (and to do so much more "gently" than whacking the drawbar with a mallet).
I would sure love to have a CAT30 spindle, but that ain't in the cards. This design does appear quite capable of providing the same drawbar tension as hand-tightening, or using an impact driver, so should get the job done. Hopefully, the new air cylinder and Bellevilles will show up today, and I can put it to the test....
Regards,
Ray L.
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OK that makes more sense the picture did not tell the whole story as to if the lower plate floated or not. (;-)
GET-R-DONE (;-)
(;-) TP
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I was under the impression the tormach holderfs/r8 setup only needed a few hundred pounds of upward pressure on the draw bar to be secure. we are running a washer stack that generates 800lbs on the mill and unlocking with a .2" stroke bimba 4" pancake cylinder , cylinder was less than $100 and I havent had a tool slip in the past couple of years of operation . I hadnt thought about the load being applied to the bearings when unlocking , I would imagine they are probably holding up OK but I am now wondering about the severe load on the ballscrew assembly on my quill . I like your idea of the locking mechanism to handle that load .
Please keep us posted on your progress. I am always fascinated by tool changers and related components.
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I was under the impression the tormach holderfs/r8 setup only needed a few hundred pounds of upward pressure on the draw bar to be secure. we are running a washer stack that generates 800lbs on the mill and unlocking with a .2" stroke bimba 4" pancake cylinder , cylinder was less than $100 and I havent had a tool slip in the past couple of years of operation . I hadnt thought about the load being applied to the bearings when unlocking , I would imagine they are probably holding up OK but I am now wondering about the severe load on the ballscrew assembly on my quill . I like your idea of the locking mechanism to handle that load .
Please keep us posted on your progress. I am always fascinated by tool changers and related components.
What kind of machine are you running, and where did you get the 800 pound number? What's interesting is NOBODY seems to know what appropriate drawbar tension is. I asked Tormach tech support, and the response amounted to "Beats the hell out of us! If you find out, please let us know!". So, what I did was put a 1/2" tool in the collet, tightened as I usually do manually, then measured the torque required to make the tool slip in the collet - came out to about 30 foot pounds. I then put the new drawbar in, and played with different stacks of bellevilles, and different amounts determined the drawbar tension was about 2000-2500 pounds, so that is what I'm aiming for. The only place I've seen any numbers tossed around, it was on smaller machines, like X2s, which certainly can get by with a lot less than my knee mill. The 2500 pounds is also in line with my initial esitmates, based on torquing the drawbar to 25 foot-pounds, which is what most of the impact-driver drawbars do. I have seen figures for drawbar stretch (0.015"), but don't know how reliable those are.
I do know my current setup can apply about 1500 pounds, and that is NOT enough - I can make the tool slip pretty easily at that tension.
Yeah, 800# seems like an awful big static load to be putting on the bearings or the ballscrews....
Regards,
Ray L.
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I am running a full size bridgeport clone , 3hp , 10x54 and havent had any problems . I mostly work in aluminum though and rarely do any drilling with that machine so mine may not be a good comparison
The 6-800lb number for r-8 collet came from an articlle in HSM about various collets somewhere in the past 15 years , I have seen 600 lbs mentioned in a thread somewhere in the past also. I would guess your 2500+ lb number is probably more accurate . My manual list a torque on the drawbar of 15-20 lbs which calculates to over 3000lb of clamping force for a 7/16x20 bolt
look forward to updates when your new parts arrive
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The Z-bot power drawbar works exactly like this See http://littlemachineshop.com/products/product_view.php?ProductID=3034&category=209730719. Brian has one running at the CNC workshop last summer, and we had it running at Cabin Fever in January..
I talked to the guy that developed it and he told me about 600-800 pounds was enough for the Tormach tools.
I built a similar, but simpler one on my Jet knee mill. I have my table move for the z axis, so my quill is free to operate by hand. I put the bellville washers under the drawbar, then I added a simple metal bridge above the top of the drawbar. To change a tool I simply drive the quill up with the hand feed until the top of the drawbar hits the bridge, then push a bit further to compress the springs and pop out the collet. It works fine, but I am a little light on the bellvilles, so I did have a collet slip once.
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I am running a full size bridgeport clone , 3hp , 10x54 and havent had any problems . I mostly work in aluminum though and rarely do any drilling with that machine so mine may not be a good comparison
The 6-800lb number for r-8 collet came from an articlle in HSM about various collets somewhere in the past 15 years , I have seen 600 lbs mentioned in a thread somewhere in the past also. I would guess your 2500+ lb number is probably more accurate . My manual list a torque on the drawbar of 15-20 lbs which calculates to over 3000lb of clamping force for a 7/16x20 bolt
look forward to updates when your new parts arrive
Yeah, I started with 900 pounds, and it's scary how easily the tool will move with so little tension. I just wish I had some direct means of measuring the tension, but I don't. Estimating from the Belleville specs and deflections is the best I can do.
Regards,
Ray L.
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Ya know, it just occurred to me, it's easy to calculate the maximum torque the spindle motor can exert on the tool, which can serve as a guide for how much torque I need to set the drawbar for. Since I'm using a VFD, max torque should be at base speed, in the lowest gear, which is 660 RPM. The motor is 3HP, so the torque is roughly 3 * 5252 / 660 = 24 foot-pounds. So, the 30 foot-pounds I've been aiming for seems like a reasonable target.
Regards,
Ray L.
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I don't have any idea of the force required to lock a tool in a collet, but my matsuura manual
has details of checking the spring stack, at least I think that's where I saw it and the figure of sliglty greater than
2000 lb sounds right.
I did work it out and the air cylinder needed the miniumum air pressure figure written on the machine 71psi, so a 6 inch[or so]
cylinder would be right.
I will check the manual tomorrow, if I remember.
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OK, I mounted the new, larger air cylinder, and new Bellevilles. I am now absolutely convinced this WILL work. It works just fine as-is, but I'm not able to get quite the "slip torque" I'm looking for on the toolholder. I'm aiming for 30 foot-pounds, and I'm not at a bit over 20. A new, longer lower plate and longer lever arm should easily get me there. At 20 foot-pounds, it works great. Apply the air, and the toolholder just falls out. I would guess my 2000# drawbar tension estimate is definitely in the right ballpark.
Regards,
Ray L.
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I checked and my drawbar is meant to have 500kg tension. Sure I saw 1000kg somewhere.
Just has a look and there are plenty of drawbar tension checkers made, look up clamprite.
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I checked and my drawbar is meant to have 500kg tension. Sure I saw 1000kg somewhere.
Just has a look and there are plenty of drawbar tension checkers made, look up clamprite.
But isn't that for a CAT30/40 spindle? Quite a different animal from R8. Getting the collet in place is easy. Getting the tool locked in solid enough that it can't spin in the collet under heavy load is much more difficult.
Regards,
Ray L.
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BT35!
I suggested looking at the draw bar checkers as they might give some clue to the force usually used.
Are these actually collets you putting in the spindle, I know nothing about R8.
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BT35!
I suggested looking at the draw bar checkers as they might give some clue to the force usually used.
Are these actually collets you putting in the spindle, I know nothing about R8.
Yes, I'm doing this with R8. I'd much prefer to have a CAT30 or some other spindle designed for ATC, but that ain't in the budget. Since the tension has to not only locate the collet in the taper, but also hold the tool in the collet, it appears the required tension is higher than for your BT35, perhaps by about 2X. It works, but takes a fair amount of tension.
Regards,
Ray L.
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Just stubled across this thread . . .interesting project. The arm is a work of art . . . I want one just to put on my desk and look at!
I don't see where a momentary 2k lb static load on the spindle bearings will do any harm, but the mechanism to prevent that is pretty clever. A sizzor arrangement would also work and not require an additional actuator. Just thinking out loud . . .
The Tormach setup is slick. First I've seen it. Tormach most certainly does know the drawbar force (or range) required . . it's a liability issue to advise on that, I would imagine. Certainly, the quality and accuracy of the spindle taper and the collet are going to have a significant effect on the force required, as will the presence and type of oil on the holders.
2,000lbs seems like a reasonable number to me for R8.
It will be fun to follow this thread . . . very 8) project.
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Just stubled across this thread . . .interesting project. The arm is a work of art . . . I want one just to put on my desk and look at!
I don't see where a momentary 2k lb static load on the spindle bearings will do any harm, but the mechanism to prevent that is pretty clever. A sizzor arrangement would also work and not require an additional actuator. Just thinking out loud . . .
The Tormach setup is slick. First I've seen it. Tormach most certainly does know the drawbar force (or range) required . . it's a liability issue to advise on that, I would imagine. Certainly, the quality and accuracy of the spindle taper and the collet are going to have a significant effect on the force required, as will the presence and type of oil on the holders.
2,000lbs seems like a reasonable number to me for R8.
It will be fun to follow this thread . . . very 8) project.
"A sizzor arrangement would also work and not require an additional actuator" - I considered that, but couldn't see a way to avoid the extra actuator, as the drawbar must be aboe to move down when not changing tools. If you see a way to do without, can you describe it?
Here's my question to Tormach tech support:
I have a Bridgeport-clone knee mill for which I want to make an automatic tool changer, using Tormach toolholders in an R8 collet. Can you advise me on the optimum drawbar tension?
And here's the response:
Funny you should ask that question. We have been trying to determine the optimum draw bar tension for a R-8 collet and have not been able to put an accurate description together for it yet. If I had something I would be happy to give it to you but I don’t. If you find something we would appreciate you letting us know. It seems to be a mystery of the industry that no one can put a real number on, but develop a feel for it working with it every day.
I have been completely unable to find *any* credible information on drawbar tension for R8. I have found several references to drawbar torque (typically 25 ft-lbs, or thereabouts), but nothing about tension, other than guesses. For real ATC systems (CAT/BT/etc), the numbers are in the 1000-3500# range, depending on which one but that's such a different animal, it's really not helpful. The only issue is getting enough tension to keep the tool from slipping. Since I rarely work with anything over 1/2", other than face mills and flycutters which are pretty low torque, I doubt I ever exceed perhaps 1/2-1HP, which is pretty low. I think about 1000# would be adequate for that. So, if I can make 2000, I'll have plenty of margin. First thing I'll do is take some really heavy test cuts, maybe up to tool breakage, and see if I get any pull-out.
Regards,
Ray L.
Regards,
Ray L.
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I tried doing this exact thing a couple years ago. The TTS, a 4 piston stage air cylinder, and bellevue washers.
IT DIDNT WORK!
Might be good for a little mill but I could not a good grip on the tool holders and I had all sorts of pull out issues. And this was with well over 1000 lbs of pull.
Simply put, the whole TTS system is flawed. There is no positive retention. Side load on these things just starts pulling them out. Ruined several parts before I gave up. Even with a drawbar I had slippage.
I ended up getting a replacement spindle for mine in 30 Taper. It was only $300 from YCI-Supermax. What a difference!
R8 sucks. You can make it better with some of the other quick change systems out there. There are a couple that use a retention knob system that converts R8 to something similar to CAT or BT tapered spindles. They have a spring loaded drawbar and an actuator on top. They would be well suited to a tool changer.
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My first notion was that liability was the hindrance, obviously it is knowledge:
"I have found several references to drawbar torque (typically 25 ft-lbs, or thereabouts), but nothing about tension, other than guesses."
This is equivalent of saying "I found the specs on voltage and amperage, but nothing on wattage" It's not like bolts were invented yesterday . . . the entire reason for torquing fasteners is to impart a specific tension (stretch) in the shaft . . . i.e. tension can be directly calculated from torque and vice versa. You're an electron guy and would not be expected to know this perhaps, but a mechanical engineer designing a tool changing system? . . . please.
As I mentioned, R8 quality varies greatly and the fit and finish has a significant effect on any tapered part like this. Also the presence of and degree of interference angle between the spindle and the collet will have a decided effect on the holding power per tension lb. There are many variables to consider, true enough, but stating that only guesses are available? Was there a development cycle at all with the tool changer setup? Did somebody just wake up one day with an idea and start manufacturing a product? They did no testing? Learned nothing? That whole statement from Tormach is incredible, in my opinion.
ON further review, I noticed that the Tormach setup had no positive drive facility. I don't think this is a viable strategy for a tool hoilder. How difficult would it be to put a dog drive type arrangement on the bottom of the spindle to engage the holders. Here again, not invented yesterday . . it's been a feature of gearboxes for at least 100 years.
As to a scissors arrangement, I do not understand what you mean by the draw bar having to move down when not changing tools, unless you are planing to continue to use the quill (which I think is also doable with some extensions) but I'll have a go at describing an example mechanism anyway. Imagine a large washer between the bottom of the spring pack and the spindle top, not attached to the spindle. The top scissor jaw simply pushes on the top of the draw bar. The lower jaw does the magic by lifting the washer which is free to float above the spindle top. All you would need it a positive stop (attached to the spindle or head) to limit the upward travel of the lower washer and when that stop was reached, continued motion of the scissor would force the collet out of the spindle. All one motion from a single actuator.
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SImpson, With a BP type arrangement and using the quill (most of us do) the drawbar has to be able to move up and down with the quill. The mechanism has to be able to disengage the springpack when running normally so it can float up and down as the quill is used.
THe main problem is using a collet holder to holder the toolholder. The R8 collet holder is marginal at BEST to hold a cutter under heavy loads.
Even changing over to a qc30/nmtb30 does not help much as there is NO provision in the spindle for a claw to grab a knob. What you may can do is find an old BT30 BP spindle that will fit. It has the provision for tool changer machanism. BUT the BT30 tool holders get HARD to find. BUT the saving grace is the cat holders can be made to work.
NOW IF someone were to come out with a BP spindle with cat30 at a reasonable PRICE they would probably become $$$$$$$$$$$ overnight.
Just a thought, (;-) TP
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I tried doing this exact thing a couple years ago. The TTS, a 4 piston stage air cylinder, and bellevue washers.
IT DIDNT WORK!
Might be good for a little mill but I could not a good grip on the tool holders and I had all sorts of pull out issues. And this was with well over 1000 lbs of pull.
Simply put, the whole TTS system is flawed. There is no positive retention. Side load on these things just starts pulling them out. Ruined several parts before I gave up. Even with a drawbar I had slippage.
I ended up getting a replacement spindle for mine in 30 Taper. It was only $300 from YCI-Supermax. What a difference!
R8 sucks. You can make it better with some of the other quick change systems out there. There are a couple that use a retention knob system that converts R8 to something similar to CAT or BT tapered spindles. They have a spring loaded drawbar and an actuator on top. They would be well suited to a tool changer.
I can tell you for a fact 1000 pounds is nowhere near enough for R8. You need more like twice that. With proper tension, TTS works just fine - I've been using it almost exlusively for a couple of years and never once had a tool so much as change position on me. This drawbar *is* working, with retention just slightly below what I get with hand-tightening. Once I rework it to provide just a bit more tension, it will duplicate the grip of the manual drawbar.
Regards,
Ray L.
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SImpson, With a BP type arrangement and using the quill (most of us do) the drawbar has to be able to move up and down with the quill. The mechanism has to be able to disengage the springpack when running normally so it can float up and down as the quill is used.
THe main problem is using a collet holder to holder the toolholder. The R8 collet holder is marginal at BEST to hold a cutter under heavy loads.
Even changing over to a qc30/nmtb30 does not help much as there is NO provision in the spindle for a claw to grab a knob. What you may can do is find an old BT30 BP spindle that will fit. It has the provision for tool changer machanism. BUT the BT30 tool holders get HARD to find. BUT the saving grace is the cat holders can be made to work.
NOW IF someone were to come out with a BP spindle with cat30 at a reasonable PRICE they would probably become $$$$$$$$$$$ overnight.
Just a thought, (;-) TP
My first notion was that liability was the hindrance, obviously it is knowledge:
"I have found several references to drawbar torque (typically 25 ft-lbs, or thereabouts), but nothing about tension, other than guesses."
This is equivalent of saying "I found the specs on voltage and amperage, but nothing on wattage" It's not like bolts were invented yesterday . . . the entire reason for torquing fasteners is to impart a specific tension (stretch) in the shaft . . . i.e. tension can be directly calculated from torque and vice versa. You're an electron guy and would not be expected to know this perhaps, but a mechanical engineer designing a tool changing system? . . . please.
As I mentioned, R8 quality varies greatly and the fit and finish has a significant effect on any tapered part like this. Also the presence of and degree of interference angle between the spindle and the collet will have a decided effect on the holding power per tension lb. There are many variables to consider, true enough, but stating that only guesses are available? Was there a development cycle at all with the tool changer setup? Did somebody just wake up one day with an idea and start manufacturing a product? They did no testing? Learned nothing? That whole statement from Tormach is incredible, in my opinion.
ON further review, I noticed that the Tormach setup had no positive drive facility. I don't think this is a viable strategy for a tool hoilder. How difficult would it be to put a dog drive type arrangement on the bottom of the spindle to engage the holders. Here again, not invented yesterday . . it's been a feature of gearboxes for at least 100 years.
As to a scissors arrangement, I do not understand what you mean by the draw bar having to move down when not changing tools, unless you are planing to continue to use the quill (which I think is also doable with some extensions) but I'll have a go at describing an example mechanism anyway. Imagine a large washer between the bottom of the spring pack and the spindle top, not attached to the spindle. The top scissor jaw simply pushes on the top of the draw bar. The lower jaw does the magic by lifting the washer which is free to float above the spindle top. All you would need it a positive stop (attached to the spindle or head) to limit the upward travel of the lower washer and when that stop was reached, continued motion of the scissor would force the collet out of the spindle. All one motion from a single actuator.
Simpson,
Since the quill is my Z axis, I kinda need it.... I am a degreed mechnical engineer, and you reallty can't get anything more than a rough estimate of tension from torque. To do that you'd need to know the drawbar stretch, and the exact material used. I have no way of knowing either. Otherwise, an estimate can be off by +/-50%, depending on the quality of the threads, the fit, materals used, etc. I did do the calculation, which is how I initialliy determined the tension needed to be in the 2500 pound range, and my experimentation seems to have proven that estimate reasonable correct. Remember, this is a knee mill, not a 30HP VMC. In normal use, I doubt I typically pull more than 1HP from the spindle, so Tormach *should* be perfectly capable of doing the job. Certainly, I've never had one move on me to date, and I've used them a LOT. I just have to get the power drawbar to duplicate the tension I set by manual tightening.
Regards,
Ray L.
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Vmax, Someone mentioned an attachment for an X2 working in 'exactly' the same way as Himmy's device. The X2 has no quill, so I was a bit confused as to how exactly the mill was set up. I've seen conversions that use the quill and those that use the knee. I can imagine advantages to both methods.
While I do agree with your assessment of the options, I think the discussion is how to make the current configuration work, and I see some potential that it can, to a point. Although as an entrepreneur, I have to admit that your idea of producing a proper spindle is intriguing. A forum like this one would presumably be the right place to message such an idea, yes?
Himmy, someone said that you were a programmer, my apologies. Still, I'm going to respectfully disagree completely with your statement about tension. The tension calculations are common and have been around forever and obviously as you pointed out, they are based on the size and pitch of the thread. The ONLY thing that is estimated it the friction. The material has zero to do with the amount of tension produced by a given torque. Weaker materials with stretch more, that is the only difference. In critical applications, if the physical arrangement allows it (or can be designed to allow it) the actual bolt stretch is measured to eliminate the friction variable. In such cases, in my experience, the actual measured stretch is very close to the predicted stretch based on torque.
The scissor mechanism could be made to ride the quill by utilizing extensions to the spindle and drawbar and having the actualtor mounted on and 'riding' the extensions as the quill went thru its travel. I think what you have is a good design that needs only some testing and refining, the scissor idea was just an interesting discussion point. It came to mind as I have used the principle in several designs over the years and I am partial to it.
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Vmax, Someone mentioned an attachment for an X2 working in 'exactly' the same way as Himmy's device. The X2 has no quill, so I was a bit confused as to how exactly the mill was set up. I've seen conversions that use the quill and those that use the knee. I can imagine advantages to both methods.
While I do agree with your assessment of the options, I think the discussion is how to make the current configuration work, and I see some potential that it can, to a point. Although as an entrepreneur, I have to admit that your idea of producing a proper spindle is intriguing. A forum like this one would presumably be the right place to message such an idea, yes?
Himmy, someone said that you were a programmer, my apologies. Still, I'm going to respectfully disagree completely with your statement about tension. The tension calculations are common and have been around forever and obviously as you pointed out, they are based on the size and pitch of the thread. The ONLY thing that is estimated it the friction. The material has zero to do with the amount of tension produced by a given torque. Weaker materials with stretch more, that is the only difference. In critical applications, if the physical arrangement allows it (or can be designed to allow it) the actual bolt stretch is measured to eliminate the friction variable. In such cases, in my experience, the actual measured stretch is very close to the predicted stretch based on torque.
The scissor mechanism could be made to ride the quill by utilizing extensions to the spindle and drawbar and having the actualtor mounted on and 'riding' the extensions as the quill went thru its travel. I think what you have is a good design that needs only some testing and refining, the scissor idea was just an interesting discussion point. It came to mind as I have used the principle in several designs over the years and I am partial to it.
I'm kinda hard to classify. My degree is in Mechanical Engineering, but I've spent most of my career designing high-speed audio and video signal processing chips, the silicon kind, and writing software - real-time embedded systems, language interpreters and compilers, etc.
Any calculation of tension based on torque has to contain a "frcition factor" term, which is tough to know with any accuracy without testing the specific fasteners in question. I have yet to see any reference that states otherwise. (http://findarticles.com/p/articles/mi_qa5357/is_200703/ai_n21284777/) Doesn't really matter, since I have now more or less measured the required tension. My comment re: knowing the material had to do with tensioning by stretch, for which you *do* have to know the material. Obviously a rubber bolt will stretch far more under a given tension load than a high-tensile steel bolt.
I chose not to make the whole assembly ride up and down with the quill, as that would require an additional 5" or so in drawbar length. The drawbar extension above the head is already an issue I've had to design around. (it wants to "whip" at speed). I do have my knee CNC'd, but it is for tool length compensation only. The knee would be too slow for use as a Z axis if I ever get into 3D work, as I plan to.
Now, if Terry made a QC spindle replacement....
Regards,
Ray L.
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Vmax, Someone mentioned an attachment for an X2 working in 'exactly' the same way as Himmy's device. The X2 has no quill, so I was a bit confused as to how exactly the mill was set up. I've seen conversions that use the quill and those that use the knee. I can imagine advantages to both methods.
While I do agree with your assessment of the options, I think the discussion is how to make the current configuration work, and I see some potential that it can, to a point. Although as an entrepreneur, I have to admit that your idea of producing a proper spindle is intriguing. A forum like this one would presumably be the right place to message such an idea, yes?
Himmy, someone said that you were a programmer, my apologies. Still, I'm going to respectfully disagree completely with your statement about tension. The tension calculations are common and have been around forever and obviously as you pointed out, they are based on the size and pitch of the thread. The ONLY thing that is estimated it the friction. The material has zero to do with the amount of tension produced by a given torque. Weaker materials with stretch more, that is the only difference. In critical applications, if the physical arrangement allows it (or can be designed to allow it) the actual bolt stretch is measured to eliminate the friction variable. In such cases, in my experience, the actual measured stretch is very close to the predicted stretch based on torque.
The scissor mechanism could be made to ride the quill by utilizing extensions to the spindle and drawbar and having the actualtor mounted on and 'riding' the extensions as the quill went thru its travel. I think what you have is a good design that needs only some testing and refining, the scissor idea was just an interesting discussion point. It came to mind as I have used the principle in several designs over the years and I am partial to it.
Oh, there are people using this same mechanism on X2s, using only about 500 pounds of tension, and the same Tormach holders. But, an X2 has a fractional HP spindle motor, and is not rigid enough to take heavy cuts, so the tool load is pretty modest, even compared to my little BP clone.
Regards,
Ray L.
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(;-) Some very smart people have been working on this for about 50 years now and so far no apparent winner.
Making a cat type spindle would be a piece of cake, "BUT" making it work in the BP enviroment, NOT so easy. There are design interface problems working with the BP spindle design (;-).
BP did have a 30 series spindle with tool changer the BT30 BUT I don't believe it would work in a standard BP/clone machine
Running a spindle like an X2 (bed mill) would be simple to do as well Just a mini type VMC you could probably use the iso 20 type holders(not cheap and hard to find)
(;-) TP
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(;-) Some very smart people have been working on this for about 50 years now and so far no apparent winner.
Making a cat type spindle would be a piece of cake, "BUT" making it work in the BP enviroment, NOT so easy. There are design interface problems working with the BP spindle design (;-).
BP did have a 30 series spindle with tool changer the BT30 BUT I don't believe it would work in a standard BP/clone machine
Running a spindle like an X2 (bed mill) would be simple to do as well Just a mini type VMC you could probably use the iso 20 type holders(not cheap and hard to find)
(;-) TP
Terry,
I don't see what the difficulty would be. I can see that perhaps the spindle nose *might* have to come down a bit, to make room for the pullstud retention mechanism. But, other than that, what's the difficulty in doing it? It sure would be a nice thing to have, but seems to me it would be $$$ to do right, since both the inside and outside would have to be precision ground.
I think in judging this kind of device, it's important to keep in mind the limits of it's utility. If I can get the tool to reliably carry 30 foot-pounds without slipping (which seems to be no problem), I don't think it's possible to exceed that on this class of machine, no matter what you do. I have only a 3HP spindle, and typically use 1/2" endmills for all "heavy" cutting, and work almost exclusively in aluminum - that's not a big load. I'm not running large tools making deep cuts at 500 IPM in hard steel.
Regards,
Ray L.
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Here's some good news! I've been doing some calculations, and I'm liking what they're showing. My "worst case" cut is a 1/2" wide, 1/2" deep, 30 IPM slotting cut in aluminum,turning about 5000 RPM. By my estimates, confirmed using several on-line machining calculators, this equates to just under 2HP at the spindle, and a tangential force of about 100 pounds. This works out to a spindle torque on the order of 30 inch-pounds, not foot-pounds. So, my 30 foot-pound target is WAY high of what should really be required. This is looking better!
Regards,
Ray L.
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GO get um RAY, (;-)
Ray the main problem is where the spindle at the midpoint NECKS down to the small splined section there is almost no room to get all the parts inside of the envelope and have a reliable design. Note I said almost.
HUM 1/2 wide 1/2 deep at 30 ipm and 5000rpm would just about stall my 3hp spindle so you are close (;-) ALSO to get to 5K I would be in overdrive so there is a reduction in Torque.
(;-) TP
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GO get um RAY, (;-)
Ray the main problem is where the spindle at the midpoint NECKS down to the small splined section there is almost no room to get all the parts inside of the envelope and have a reliable design. Note I said almost.
HUM 1/2 wide 1/2 deep at 30 ipm and 5000rpm would just about stall my 3hp spindle so you are close (;-) ALSO to get to 5K I would be in overdrive so there is a reduction in Torque.
(;-) TP
Terry,
"where the spindle at the midpoint NECKS down to the small splined section there is almost no room to get all the parts inside" - Yup, that's why it *might* be necessary to extend the spindle downward just a bit - certainly no more than 1". I actually think the design would be pretty easy - It's the fab that difficult.... Just as with mine, the spindle would have to get a LOT taller out the top, as it would require a mighty long stack of Bellevilles to get the required travel to release the pullstud.
Regards,
Ray L.
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The complexity of a release mechanism that travels with the spindle should be considered in the total project scope along with the complexity of the tool changing mechanism for a 'home brew' changer, methinks.
I have no idea at this point what you are contemplating for a tool changing mechanism, but since you are moving the quill into a fixed postion to release the tool it is a safe assumption that the tool changing mechanism will need to move the tools around.
With a release mechanism that travels with the spindle, then quill could be utilized to place and pick up the tools, eliminating the need for a tool changing mechanism. Aluminum air cylinders weigh practically nothing and the arms could be made from high strength materials keeping the physical size very small, so the weight of the release mechanism would be negligible compared to the rest of the mass being moved.
The scissor could probably be arranged vertically (I've not though that thru) so that the actuator could ride centered on top. The spindle extention tube could contain the travel stop and also center the drawbar at the top via a simple slip bearing. If the spindle has a threaded preload nut, the extension could be made to replace it and thread onto those existing threads. It would then serve the function of the preload as well as extend the spindle.
Again, I can see that what you have already looks fine and workable, I'm just enjoying the conversation here.
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The complexity of a release mechanism that travels with the spindle should be considered in the total project scope along with the complexity of the tool changing mechanism for a 'home brew' changer, methinks.
I have no idea at this point what you are contemplating for a tool changing mechanism, but since you are moving the quill into a fixed postion to release the tool it is a safe assumption that the tool changing mechanism will need to move the tools around.
With a release mechanism that travels with the spindle, then quill could be utilized to place and pick up the tools, eliminating the need for a tool changing mechanism. Aluminum air cylinders weigh practically nothing and the arms could be made from high strength materials keeping the physical size very small, so the weight of the release mechanism would be negligible compared to the rest of the mass being moved.
The scissor could probably be arranged vertically (I've not though that thru) so that the actuator could ride centered on top. The spindle extention tube could contain the travel stop and also center the drawbar at the top via a simple slip bearing. If the spindle has a threaded preload nut, the extension could be made to replace it and thread onto those existing threads. It would then serve the function of the preload as well as extend the spindle.
Again, I can see that what you have already looks fine and workable, I'm just enjoying the conversation here.
Simpson,
Nope, the toolchange mechanism does not have to move at all - I have a quill AND a knee. So, while the quill is fixed during a toolchange, I am still free to use the knee and X/Y axes to do the tool pick and place. So, I get the best of both worlds. The weight of the drawbar mechanism is a non-issue. As I said, it's the extension of the drawbar above the head that is an issue. I am "housing" the drawbar in a tube that replaces the preload nut on the top bearing inner race, but since I run over 8K RPM, it's still not a great idea to make this any longer than absolutely necessary. The floating drawbar assembly would require extending this at least another 5-6", which is a LOT.
With luck, I'll get the guide tube machined this AM, and be able to run the first at-speed tests today. Now that I feel I have a good handle on the required drawbar tension, I'm pretty optimistic about the whole thing. Crossing my fingers and toes....
Regards,
Ray L.
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YEP that part above the spindle shaft is the real problem. It needs to run dead nuts true or you get a wobble. THat wobble creates havuc at speed.
That has been one of the main problems in the past. The extension above the splined portion needs to run in a bearing set to keep it true to the spindle but it would also need to float inside of the upper housing as well.(;-)
I remember seeing an R8 unit in the past that worked with a pull stud on top of the toolholder can't remember exactly where it was. I remember it used a ball type claw to grab the stud and it used a Royal R8 quick change adaptor setup in the spindle.
I todays world getting the spindle made should not be a problem IF you can work out the upper details. This is where the problems have never been resolved (;-)
Just a thought TP
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Himmy,
We're on the same page here. What I called an 'extension', you are calling a 'guide tube' . . same function . . even down to using the existing threaded pre-load as the base for the tube.
I'm not feeling the same concern as you and Vmax for the wobble. A machined concentric tube of less than 2" in diameter turning under 10k RPM that is under 12" long (all guesses) should not be trying very hard to get off the top of your mill, unless you cannot keep it aligned with spindle center for some reason. If it worrisome to you, just reduce the mass by making the guide tube thin and lightweight and rigid by using 7075. Keeping the draw bar centered in that tube would be an easy matter of a concentric bushing perhaps of a lightweight self lubricating plastic like Delrin, again very little weight and no balance issues.
It occurs to me that the draw bar extension would not need to be very large diameter beyond the collet threads. I find that pre-ground 'stressproof' steel rounds are very straight and I think the collet threads are 5/16" which would be more than needed for the rest of the shaft, methinks, so you could turn that down to reduce the mass above the spindle also, but I just am not seeing a problem with wobble since as far as I know, nothing is extending out from the tube or the drawbar shaft.
I guess you'll know soon enough! I'm anxiously awaiting pics of your next few pieces.
BTW, now that you have mentioned it again, I do recall you saying you had the CNC on the knee as well as the quill. Probably not many conversions are that extensive, one might imagine.
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Ray you must NOT have a standard BP type spindle (;-)
I can't see any way to use a long tube as a preload nut with a BP spindle. Picture enclosed of a BP spindle shaft with bearings installed.
(;-) TP
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Heres the setup on my Beaver Mill, the beauty of it is the drawbar can be activated at any quill position.
Hood
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Himmy,
We're on the same page here. What I called an 'extension', you are calling a 'guide tube' . . same function . . even down to using the existing threaded pre-load as the base for the tube.
I'm not feeling the same concern as you and Vmax for the wobble. A machined concentric tube of less than 2" in diameter turning under 10k RPM that is under 12" long (all guesses) should not be trying very hard to get off the top of your mill, unless you cannot keep it aligned with spindle center for some reason. If it worrisome to you, just reduce the mass by making the guide tube thin and lightweight and rigid by using 7075. Keeping the draw bar centered in that tube would be an easy matter of a concentric bushing perhaps of a lightweight self lubricating plastic like Delrin, again very little weight and no balance issues.
It occurs to me that the draw bar extension would not need to be very large diameter beyond the collet threads. I find that pre-ground 'stressproof' steel rounds are very straight and I think the collet threads are 5/16" which would be more than needed for the rest of the shaft, methinks, so you could turn that down to reduce the mass above the spindle also, but I just am not seeing a problem with wobble since as far as I know, nothing is extending out from the tube or the drawbar shaft.
I guess you'll know soon enough! I'm anxiously awaiting pics of your next few pieces.
BTW, now that you have mentioned it again, I do recall you saying you had the CNC on the knee as well as the quill. Probably not many conversions are that extensive, one might imagine.
Simpson,
Well, due to an oopsie on my part, my first attempt at the guide tube did not seat properly, and ended up with 0.050" runout at the top - not good. At 8K RPM, it made some pretty good vibration! I corrected that, and I'm now under 0.005". With a more suitable lathe, I'm sure I could do better. But, the vibration is pretty small at this point, even at top speed. Probably tolerable as it is. Certainly good enough for now.
The collet threads are 7/16-20. I'm using a high-strength all-thread for the moment. Once the dimensions are all settled, I'll probably make something better. The Bellevilles and their supporting "top hats" stick out of the tube when the drawbar is up. They are partially exposed through most of the quill travel. But, they are always guided by the tube, so no problem there.
I first converted the knee. In fact, I still haven't done the quill. But, the knee is too slow, and there's too much wear and tear on the gears, screw, etc. for that to be the long-term solution. A quill drive is the next major project.
Terry,
My spindle is not a real BP, but is nonetheless identical to your picture. The front pulley is supported by two bearings fixed to the top housing. It is those bearings I am attaching the guide tube to. They, too, have to be concentric to the main spindle bearings, or you get a lot of rattling from the dog clutch and other things up there.
Regards,
Ray L.
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Hood,
I assume that a CAT-something spindle, right? So the drawbar tension is lower, allowing a more compact arrangement that can easily slide up and down with the quill.
Regards,
Ray L.
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Ray, it is a 40 taper, not sure what the clamping tension is but that is a hydraulic cylinder running at 900PSI.
Hood
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Just looked in the manual, no mention of tension but there are 112 bellevilles so would be a fair bit I think.
Hood
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Ray, it is a 40 taper, not sure what the clamping tension is but that is a hydraulic cylinder running at 900PSI.
Hood
Whoa, baby! Where do you get 900 PSI? I assume that's hydraulic, not pneumatic?
Regards,
Ray L.
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Yep, 4 words before the 900PSI is the clue :D
Its an air powered intensifier.
Hood
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Yep, 4 words before the 900PSI is the clue :D
Its an air powered intensifier.
Hood
Hood,
What, now you expect me to read ALL the words?? :-) Hydraulics would solve a whole lotta problems, but, sadly, too expensive for me....
Now, that "air powered intensifier" is interesting. I'd never heard of that.
Regards,
Ray L.
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Oops, yes, I meant 7/16" on the drawbar thread . . . you certainly would not be turning a lot of meat off if you were starting with only 5 . . :-[
Hood, hard to tell from the photo how big that gizmo is, but I think you have big machines so at a guess the cylinder might be 3"?? that would be over 6,000 lbs of force. Prolly enough :-\
Any chance of seeing what's inside that thing?
Ray, If a wave of motivation overtakes me, I'll be doing an X3 mill. Oddly, what I am after other than the larger size is the quill. In my case, I would not CNC the quill as I would want it for the occasional drilling or tapping job. I have a Tapmatic head and that thing is 8), but a lot of trouble to put up just to cut one or two threads.
I've read a few blogs and articles about CNC quills, but in each case, I just can't see how a non-adjustable rack and pinion is going to produce the required accuracy. If I was heading that way, I'd want to try to rig a ball screw even if I had to run it thru a lever of some sort. Another option that exists but I have not seen anyone use is to split the pinion and put a very stiff spring between them to take out all of the lash. Not to get ahead of you, but what is your plan for the quill?
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Ray,
of course I do, I like being the only one that doesnt ;D
Simpson
Its a bit under 3 inch, the OD is 70mm or so, ID will be probably about 60mm.
I have more pics of it dismantled at home so can post tonight if you want.
As to quills, usually you fit a ballscrew on the front, I did a manual Bridgeport as my first conversion and again have pics but they are at home.
Hood
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Heres some pics of the setup.
First pic is the housing that the cylinder slides in, there are two dogs that fit in the cylinders groove to stop it rotating.
Next pic is the cylinder and the attached guide tube for the drawbar. There is a left hand thread inside the tube and the tube rotates with the spindle, there is a bearing at the lower part of of the cylinder for this.
Next is an inside view up the guide tube and you can see the thread and the lower part of the ram.
Next is a pic of the spindle showing the left hand thread.
Hood
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Heres is a pic of the top of the drawbar and lastly a pic of the quill bracket I made to convert my manual Bridgeport to CNC.
Hood
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Hood, let me just comment that your dedication to this forum is nothing short of amazing to me. Forums are very expensive, time wise, and you spend a lot of it helping people out. Just wanted to acknowledge.
What I can gather form the photo of the drawbar mechanism looks like something similar to what I had in mind, except that using htdraulic power eliminates the mechanical advantage required for an air cylinder. i.e. no scissors. Hydraulics are arguably more expensive (depends really on what you already have aroud the shop) and certainly a lot heavier mass to move around. On the other hand, it will probably perform for 30 years like the day it was installed, save an new o-ring here or there.
The quill drive is a nice clean deisgn and is also what I envisioned as the way to go for a quill drive. Yours is the first I have seen and it looks to be very beefy. I don't know why, but that's what I expected from Hood . . rugged, non nonsense, bullet proof.
Others have attacked the problem by motorizing the rack, which probably seems logical at first thought.
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Simpson
Air over oil can probably get round the expense issue but suppose that depends on whether you have access to cheap air and hyd cylinders, working repairing boats hydraulics are fairly easy for me to obtain, air not so easy but eBay is wonderful ;D
I was fortunate that this is standard equipment on the mill so no thought at all had to go into it from me thankfully ;D
Quill versus knee and ballscrew versus rack will always be debated, personally my thoughts are quill with ballscrew for fast work and knee for tool offsets is the best way, well bedmill is the best way but I dont have one and probably never will due to headroom, so thats not an option. The Beaver has an induction motor on the knee so fitting a servo would not be a problem, maybe an alteration to the mount and thats it. It does however just have a leadscrew on it but I am hoping the backlash is linear so comp should work well and the weight will negate any problems with tool trying to lift it I think ;)
Rack would be, I think, hard to get any kind of backlash free accuracy from so never considered it, the comp could be used I suppose but then the tool could push and pull it so some form of damping/lock would be needed, again not impossible but would it be worth the hassle?
Hood
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HIYA RAY, HOW is it going?? Any more news ?? pictures???
(;-) TP
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HIYA RAY, HOW is it going?? Any more news ?? pictures???
(;-) TP
Terry,
Busy with other things for a few days. I've gotten some re-machining done, and the mount plate fabbed, so I'm close to putting it on for a real test. My only remaining concern is getting the runout/balance on the guide tube under control. I need to make a new, aluminum, guide tube, and do it on a better lathe so it's as true as possible. Any runout/imbalance on that causes chatter on the dog clutch on the spindle, which will cause wear. I can test it with the tube I've got, but don't want to run it too long. I may just remove the dog clutch and replace it with a solid coupling, since I never use the backgear anyway.
Regards,
Ray L.
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I did find a source for a BP qc30 spindle shaft that is an extra 6" long at the top(;-) that would give us the extra reach needed for the top mechanism to clear without adding the tube as the springpack would ride directly on the top of the shaft and it would be long enough to clear on all quill operations.
I think there is room inside the shaft to make the adaptor for the claw mechanism (;-)
MIGHT just have to try one. (;-) Can't let you have ALL the fun.
(;-) TP
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I did find a source for a BP qc30 spindle shaft that is an extra 6" long at the top(;-) that would give us the extra reach needed for the top mechanism to clear without adding the tube as the springpack would ride directly on the top of the shaft and it would be long enough to clear on all quill operations.
I think there is room inside the shaft to make the adaptor for the claw mechanism (;-)
MIGHT just have to try one. (;-) Can't let you have ALL the fun.
(;-) TP
Terry,
How many $$$$ was it?
I don't understand how that can work - can you provide a link? I don't see how it's possible for the spindle to be any larger than the splined part, as that has to pass through the dog-clutch....
Regards,
Ray L.
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The splined part is 6" longer allowing it to stick up above the top .
(;-) TP
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are they from a series 1 CNC?
Hood
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HOOD I believe so, I think the cnc version is longer to account for the drive assy for the quil screw. That should work well for a standard series 1 head. It would leave the top of the shaft out of the top of the machine. You would just need to make sure you got the CNC shaft that has the hole in it. That woul d eliminate the problem of the wobbly tube as the springpack could mount directly to the top of the shaft.
Then if you coul dhave the spindle machined for the claw mechanism you woul dhave a true tool changer just like the big boys and you coul deven use CAT30 tool holders, just change out the drive lugs to fit the cat30.
Just a thought, (;-) TP
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Before you buy make sure it will fit, what I mean by that is the series 1 CNC with the rigid ram have the hollow ballscrew that the spindle passes through so there is no need for the spines at that part. Maybe all are not the same but mine definitely has quite a bit of un-splined shaft above the top bearing where a standard Bridgeport spindle the splines start right after the top bearing.
Hood
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This seems similar to this system.
www dot mach-1tooling dot com
I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.
Kenny
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Resplining would not be a problem(;-) nor would be remachining the outside to fit . I do have a series 1 boss 5 ( BOSS HAWG) converted to Mach.
I was just thinking for the average joe with a std series 1 it may be an option IF they wanted a Tool changer option. MOST don't as the R8 stuff is CHEAP CHEAP compared to QC30 or CAT30 stuff.
Just a thought, (;-) TP
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This seems similar to this system.
www dot mach-1tooling dot com
I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.
Kenny
Kenny,
I find that system fascinating. The pullstud mechanism is precisely what I had in mind for a future "upgrade" to my setup, and proves that it CAN be done. What really surprises me is the very low drawbar tension - apparently only 600#? After my testing the last few weeks, I'm amazed that's enough to securely hold an endmill in a collet. Do you by any chance have a means of measuring (even crudely) how much torque it takes to make a 1/2" endmill slip in a collet using that setup? I was able to do it by clamping a vise grip on a scrap endmill, and using a $5 hardware store "fish scale" to pull on the handle, then calculate the torque based on the fishscale reading and the length of the vise grip. That would be invaluable in helping me correctly calibrate my drawbar.
I'm going to read their patents and see what I can learn....
Regards,
Ray L.
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Ray,
Look a little closer. They use a collar to clamp up the collet so that the drawbar is only holding the collet in place. That gives the ability to setup tools with a constant z-offset. Neat huh? Pricing is not too bad. You could get away without their release and use the one that you have too.
Kenny
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Resplining would not be a problem(;-) nor would be remachining the outside to fit . I do have a series 1 boss 5 ( BOSS HAWG) converted to Mach.
I was just thinking for the average joe with a std series 1 it may be an option IF they wanted a Tool changer option. MOST don't as the R8 stuff is CHEAP CHEAP compared to QC30 or CAT30 stuff.
Just a thought, (;-) TP
I have to wonder why nobody is talking about making a spindle from sratch . . . by the time you get done all those modifications . . . .
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Ray,
Look a little closer. They use a collar to clamp up the collet so that the drawbar is only holding the collet in place. That gives the ability to setup tools with a constant z-offset. Neat huh? Pricing is not too bad. You could get away without their release and use the one that you have too.
Kenny
Kenny,
I did notice that, but the way I read their intent, you only need to use that if you want to maintain the tool length when the collet is removed fron the spindle. I see nothing indicating you cannot just use the collet alone if you're not concerned with maintaining tool length.
I did just perform a test on my machine. I took the stock drawbar, removed the top spacer, and replaced it with a short stack of Belleville washers. I then tightened the drawbar enough to give a tension of roughly 900#, and loaded my worst (dullest) 5/8" endmill, and took a heavy cut. The endmill did not move. I then measured the "slip torque" at about 10 foot-pounds, compared to the roughly 25-30 inch-pounds of cutting torque on the tool.
Regards,
Ray L.
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Resplining would not be a problem(;-) nor would be remachining the outside to fit . I do have a series 1 boss 5 ( BOSS HAWG) converted to Mach.
I was just thinking for the average joe with a std series 1 it may be an option IF they wanted a Tool changer option. MOST don't as the R8 stuff is CHEAP CHEAP compared to QC30 or CAT30 stuff.
Just a thought, (;-) TP
I have to wonder why nobody is talking about making a spindle from sratch . . . by the time you get done all those modifications . . . .
You mean aside from the fact that it would be stupid expensive? I sure don't have the equipment to do it. You'd start with a couple hundred $ worth of good stock (~4" dia. by 3 feet long?), get it turned, precision bored, broached, then hardened and precision ground, inside and out. By the time you were done, I'd guess you'd have easily $1000 in it, and have no guarantee it would even work.
This does, however, suggest a trivial solution. If the required tension is truly only 600#, I would have no problem at all applying that force to the spindle bearings - they're MORE than large enough to handle that with ease. A *slightly* longer drawbar (perhaps 2") could then be constructed to accomodate a stack of Belleville washers to provide the 600# tension. Just like this thing, releasing the tool would require nothing more than mounting a "cap" over the top of the spindle that would contact the drawbar about 0.100" *before* the spindle hits the upper limit of travel. Run the spindle all the way up, and the tool releases. It doesn't get any simpler than that!
This, of course, is all based on that 600# being a good number. I'm gonna have to do more tests this weekend....
Regards,
Ray L.
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Ray,
I would change the Mach1 release mechanism for yours. That way a bad move or z axis runaway won't let a tool loose in your shop.
The collar definitely adds to the turning torque resistance applied to the cutter. You get the clamping force of the cutter nut added to the drawbar force. They also use a clamp collar to the spindle for very heavy loads. I have seen lots of shops use the collet clamp sleeve without the nut for many smaller cutter sizes.
Kenny
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Ray,
I would change the Mach1 release mechanism for yours. That way a bad move or z axis runaway won't let a tool loose in your shop.
The collar definitely adds to the turning torque resistance applied to the cutter. You get the clamping force of the cutter nut added to the drawbar force. They also use a clamp collar to the spindle for very heavy loads. I have seen lots of shops use the collet clamp sleeve without the nut for many smaller cutter sizes.
Kenny
Kenny,
I am VERY glad you posted the link to the Mach1 drawbar. It has forced me to re-evaluate what I've done, and I found a significant error in one of my base assumptions. I'm going to go do some thinking, but I think I can see how to resolve the problems I have with my current design. This will, I think, let me greatly shorten the drawbar and guide tube, and, with luck, eliminate the balance/runout/whipping issues.
Regards,
Ray L.
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OH there have been many many systems over the years for R8 conversions none have survived for one reason or the other.
Heres another one
http://www.snapchange.com/r8-toolchangerproducts.htm
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I think that there are lots of people representing them. I found the manufacturer though. Better pricing and the ability to work out a deal on what's included in the kit. I have used them for years and they work well if used correctly.
Kenny
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OH there have been many many systems over the years for R8 conversions none have survived for one reason or the other.
Heres another one
http://www.snapchange.com/r8-toolchangerproducts.htm
Terry,
That one is interesting, and seemingly very simple. Any idea what it costs? It appears to require non-standard tool holders?
Regards,
Ray L.
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This seems similar to this system.
www dot mach-1tooling dot com
I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.
Kenny
This is interesting, but it is not an automatic tool changer.
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This seems similar to this system.
www dot mach-1tooling dot com
I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.
Kenny
Kenny,
I find that system fascinating. The pullstud mechanism is precisely what I had in mind for a future "upgrade" to my setup, and proves that it CAN be done. What really surprises me is the very low drawbar tension - apparently only 600#? After my testing the last few weeks, I'm amazed that's enough to securely hold an endmill in a collet. Do you by any chance have a means of measuring (even crudely) how much torque it takes to make a 1/2" endmill slip in a collet using that setup? I was able to do it by clamping a vise grip on a scrap endmill, and using a $5 hardware store "fish scale" to pull on the handle, then calculate the torque based on the fishscale reading and the length of the vise grip. That would be invaluable in helping me correctly calibrate my drawbar.
I'm going to read their patents and see what I can learn....
Regards,
Ray L.
Ray, isn't this apples to Oranges? This is not an autromatic tool changer. The 600# is not applicable to your setup. You are relying on friction alone to turn the tool. This setup is using the R8 collet which has a psitive drive. The drawbar has only to keep the toolholder in the spindle and 600# is plenty for that.
I continue to think your #2000 number is closer to the mark. I'm sure you are familiar with breakaway torque and I think the 'problem child' in a friction hold is going to be chatter, where you are going to see extraordiarily high shock loads which are powered by the inertia of the rotating mass and not by the motor HP.
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Couple more thoughts:
Making a spindle from scratch: That comment was made to Vmax who apparently has the capability to machine a spindle, and who also presented the idea of someone making a custom spindle as a product. Many moons ago when I had my own small shop for building prototypes and specialized high strength parts, I did my own heat treating and had a tool post grinder, so like anything else, no big deal if you have the tools for it.
That said, I don't think the spindle is, or should be hardened, except perhaps case hardened to a few tens for durability. Spindles are subject to shock loads from chatter and hardened steel is not a good choice for shock loading, unless you are talking about S7, which IS expensive, is precisely hardenable to a specific depth, but you would still leave the core soft and you would still have to be stress relieved after hardening and before grinding.
I presume you can still buy pre-hardened and stress relieved machinable rounds? I used a lot of this stuff before I got my own furnace. However, I think for the purposes we are talking about here, a new spindle made from stressproof steel round with no heat treatment at all would be adequate. I would grind only the R8 taper and then only after the bearings were installed and it was in the head already. I replaced the pathetic bearings in my X2 head and then re-ground the R8 taper and I show zero runout on a .0005 reading Starret, which is more than adequate for my purposes.
Positive drive: Auto-changing an R8 is frought with challenges, but it seems to me that the Tormach setup could be easily modified for positive drive, potentially halving the tension requirement on the drawbar.
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Here is a Prototype I made for a Tormach......
http://video.google.com/videoplay?docid=8421475437071753563
I ended up having to double the Power of the Cyclinder and double the power of the Beviels, that allowed me to have a consistant 3/8th inch cut.........but NO deeper, things would pull out.......
This ATC has a DL06 PLC coupled to mach for the ATC control, and used Air for the Drawbar piston, and swing arm piston.
The idea works, but for it to be something I would stand behind legally, I would have to add some kind of positive locking Pull stud to the R-8 System, That would push the cost even higher......
scott
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Here is a Prototype I made for a Tormach......
http://video.google.com/videoplay?docid=8421475437071753563
I ended up having to double the Power of the Cyclinder and double the power of the Beviels, that allowed me to have a consistant 3/8th inch cut.........but NO deeper, things would pull out.......
This ATC has a DL06 PLC coupled to mach for the ATC control, and used Air for the Drawbar piston, and swing arm piston.
The idea works, but for it to be something I would stand behind legally, I would have to add some kind of positive locking Pull stud to the R-8 System, That would push the cost even higher......
scott
Scott,
How much drawbar tension are you running? Any pictures?
Regards,
Ray L.
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2,400 lbs approximatly in belviels,
Pics of the build are under the tormach thread of the cnc zone.
scott
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2,400 lbs approximatly in belviels,
Pics of the build are under the tormach thread of the cnc zone.
scott
Scott,
So, with 2400#, you can't cut deeper than 3/8" without pull-out? That would not do me at all.... By my calculation, I manually tighten the drawbar to about 4500#, but that seems severe overkill to me. How have you verified that tension? What kind of cut woudl cause pullout - what tool, RPM, feed, etc.? I just yesterday tried a 5/8" endmill at only about 500# tension, and saw no pullout....
Regards,
Ray L.
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Ray, Scotts piece was a real work of art I have a picture of it on the wall in the shop as inspiration. What is really the heart of ANY tool changer is going to be a workable spindle WITH the tool change claw to hold the tool holder. There are ISO20 tool changers used on routers and then you could do cat30 type.
There are also some R8 adaptors that MIGHT be able to be adapted to a working solution. They have lugs to keep the tool locked and use tool holders NOT collets.
STILL though the claw mech is the bogie bear to any good tool changer.
AS to the spindle I would use a quality steel and have it NITRIDE hardened on the surface. Then do a deep cryo cycle to stress relieve and then finish grind to spec. You would also need to make sure the area inside the shaft where the claw mechanism would work is hard as well to prevent wear. Make sure to harden the spline area as well.
(;-) TP
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Terry,
Thanks for the chops........ (btw, did you like that hotswap I sent your way.........?)
Ray,
I was building it for an aftermarket "Plug and Play" ATC for the tormach. But, the guys on the CNC zone in the tormach thread, said, that it must be able to cut
a 1" depth of cut, with a high flute 1/2" AL mill bit with out pulling out....... Just like a video on Tormach web site shows there tool holders doing.
I was cutting ok at 3/8" no problems. But at a 1" depth of cut it was a no-go. I was unwilling to take the liability risk in selling it as is, even with the statement, dont cut
past 3/8", because sure enough, someone would, and then here comes the lawyers.......
Greg had given me a "Price Point" that he did not want me to exceed of max 3k per unit (1/2 the cost of the Tormach). To get it to hold reliably my opion is that I would
need to add a Pull Stud on the R-8 collet, and a locking Cam as well. That would have added another level of complexity to the system. Realistically, it would have pushed up the price past Gregs price point, since I would have to factor in, Support, warrently, insurance etc.
The one I build was targeted at the "Industrial/Commercial" client, not the hobbiest, thus the high price point. It was build to industrial standards, the PLC and ATC controls
where in a Nema 4 enclosure, there was a DL06, BOB, stepper amp, SMC manifold/with solinoids, Proxes on the physical ATC for error cheaking/movements.
Tell you what, I will sell mine to you including the I.P. for 8k, (includes the M6 and other macros/brians), you can then add the Pull stud system... heheehe
scott
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Terry,
Thanks for the chops........ (btw, did you like that hotswap I sent your way.........?)
Ray,
I was building it for an aftermarket "Plug and Play" ATC for the tormach. But, the guys on the CNC zone in the tormach thread, said, that it must be able to cut
a 1" depth of cut, with a high flute 1/2" AL mill bit with out pulling out....... Just like a video on Tormach web site shows there tool holders doing.
I was cutting ok at 3/8" no problems. But at a 1" depth of cut it was a no-go. I was unwilling to take the liability risk in selling it as is, even with the statement, dont cut
past 3/8", because sure enough, someone would, and then here comes the lawyers.......
Greg had given me a "Price Point" that he did not want me to exceed of max 3k per unit (1/2 the cost of the Tormach). To get it to hold reliably my opion is that I would
need to add a Pull Stud on the R-8 collet, and a locking Cam as well. That would have added another level of complexity to the system. Realistically, it would have pushed up the price past Gregs price point, since I would have to factor in, Support, warrently, insurance etc.
The one I build was targeted at the "Industrial/Commercial" client, not the hobbiest, thus the high price point. It was build to industrial standards, the PLC and ATC controls
where in a Nema 4 enclosure, there was a DL06, BOB, stepper amp, SMC manifold/with solinoids, Proxes on the physical ATC for error cheaking/movements.
Tell you what, I will sell mine to you including the I.P. for 8k, (includes the M6 and other macros/brians), you can then add the Pull stud system... heheehe
scott
Scott,
1" DOC with a 1/2" endmill seems a bit over-aggressive to me.... But I normally rough with a 1/2" 3-flute, 1/2" DOC, 30 IPM for a full slotting cut. Do you think it'll do that safely? If you've followed this thread, it appears to me that at a 2000# drawbar tension, the torque capability of the Tormach holder is at least 10X the worst-case actual continuous cutter torque, which seems to me plenty of margin for handling any impact loads and other transients. But, if your experience says otherwise, I'd like to understand the limitations as well as possible, before sinking any more time and money into this.
Regards,
Ray L.
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Ray,
just wondering if you ever considered the impact wrench type powerdrawbar for this? If you did was there a reason you decided against it?
Hood
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Ray the problem you wil run into with the tool moving in the collet holder is from 2 things .One is the short taper of the r8 and 2 is the impact load of each flute .
The tool sets up a resonate vibration which causes the taper to hinge on itself. This when the frequecy is right will allow the holder to release the tool microscopicly in stages. Over a short period those stages add up and the tool has moved under the directional load of the helix.
SCOTT, the hot swap is a cool tool. I will NOT be converting the BOSS over to a tool changer but I will use a carrasel to hold the tools needed. I will be the robotic arm (;-) so it is still very usefull as a tool platform to present the tools for each program. That in itself MIGHT be an interesting product. A tool carrasel to hold and present the tools needed for each job powered by Mach3. Just load up the tools and mach will present you with each tool AS needed. (;-) Simple to make and HANDY as all get out. The HOTSWAP would make it very practical to boot as when you changed out the tool the new tool would take the place of the old tool (;-) The Hot Swap TOOL carrasel is a marketable product with little to NO liability(;-)
We are still looking for a good donor VMC to do a complete retrofit complete with tool changer, that coupled with the new Version of Mach M3v4 will be the cats meow.
On the THC we went ahead and bought a kit from Tom C. , needed to get it done and working. SORRY :-(
(;-) TP
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Ya know, another approach occurs to me.... Let's assume we do require even 5000# of drawbar tension. This is trivial to achieve with Belleville washers. The only "gotcha" is how to generate the even larger force required to release the drawbar. Getting 5000# force with pneumatics is difficult - it requires either very high pressure, and/or a very large (and $$$$) cylinder, and/or some major mechanical advantage. However, a simpler approach just occurred to me - Compress the springs using a scissors arrangement (like I already have), powered by a screw, driven by a stepper or servo with a very high mechanical reduction. After all, speed is not an issue. The torque required would, I think, be easily generated by a stepper with a large reduction. With the existing mechanical advantage (6:1), the torque on the screw would be only about 5 foot-pounds....
Regards,
Ray L.
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Ray have you check inside the spindle to see how much room is in there above the toolholder?? May be room enough to setup a claw mech and just use an R8 with a pull stud. ?????? May have to shorten the R8 to have room??? I would work towards that end for simplicity. R8 tool holders are low cost compared to ANY Other solution.
BUT before you give up TRY what you have (;-) You may be surprised. The grip on the tool holder can be effected by the surface finish. A turned holder will NOT have the grip a ground holder will (;-) do to the actuall surface contact area. DON"T stop developing intill YOU see it as NOT good enough OR the large lady with horns on her hat sings.
I also would run as large a diameter for the tool holder stub as I could. Largest collet holder 3/4 or 1" ????? I think if you stayed in the 3/8" tool range it would work just fine After all it is a cnc and you can take as many smaller cuts as needed. It is not like you are standing there CRANKIN the handles all day (;-)
I saw earlier that one of the small Xseries 2,3,4,5 etc of bedmills is using a simalar setup with a large diam stub and a slot for the changer grip arm. Look on You tube I think X4 tool changer
GIT_R_DONE DAWG
SIDE note: NEVER stop a developement project JUST because someone said it won't work (;-) I have done a LOT of things in the past that weren't suppose to work. (;-)
Just a thought, (;-) TP
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RAY here is the Youtube example
http://www.youtube.com/watch?v=6CChUHOAknc
With you upper mech and this lower setup I believe you will be just fine (;-)
Just a thought , (;-) TP
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I think I will add a pull stud with lock on my project as time/money permits.......
scott
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RAY here is the Youtube example
http://www.youtube.com/watch?v=6CChUHOAknc
With you upper mech and this lower setup I believe you will be just fine (;-)
Just a thought , (;-) TP
Terry,
First, I haven't given up yet, but I'm close. And not because anyone else said it wouldn't work, but because I have other things to do, and this project has already taken far more time and money than I had hoped. I originally considered both this approach, and the impact wrench approach. The impact wrench had the advantage of being dirt cheap ($50?), though it seems crude to me. This approach had the (apparent) advantages of simplicity and elegance. However, the decision was based on the assumption that the required drawbar tension was in the 1000# range. This assumption was wrong - the required tension is as much as 5X that, which gets very difficult to deal with. Had I known that at the outset, I would never have gone down this road. Getting above about 2000# becomes quite difficult. What I have, even in it's original incarnation, would work just fine on a small mill, like and X2 or X3, with perhaps 1000# tension, but is not up to the loads of a full-size knee mill. I am running production, so going to smaller tools/more passes is REALLY unattractive.
That one in the YouTube video is an X3, and I'd be willing to bet the owner considers a 0.100" cut with a 3/8" endmill to be *really* heavy. I run all day long at 1/2" DOC, or more, at fairly high speed (30+IPM), so having a tool pull out would be a very bad thing, in terms of scrapped material, lost time, and potential danger.
In retrospect, I tend to think the impact wrench approach is the simpler, cheaper, and safer, way to go. But I still think it's crude. Adding a pull-stud does nothing to mitigate the problems with this approach, unless I give up collets entirely. It is the very high drawbar tension requirement that is the issue, and that is just a fact of life with R8. I am going to consider this approach - in fact, I did very early on - but it presents a different set of problems. For one, I don't know how you make an ATC to swap R8 tools. At a minimum, it would require removing the alignment pin, which I'm not real keen on. It greatly increases the vertical room needed to make a toolchange - though at least alignment would be easy, since the "mouth" of the spindle is so large compared to the top end of an R8 tool.
Regards,
Ray L.
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The Mach1 system reveals the secret here. There are really two issues to consider.
First is locking the tool holder to the mill. That's going to be a function of the surface area of the R8 taper and the pull force. I am not too surprised that 600 lbs suffices for that force, even with quite a lot of "work" being done by the spindle.
But there is a second force, and the way it works is hugely counterproductive to the first. That second force is the squeeze on a collet to hold the tool. It doesn't exist with solid tool holders, and it is the reason the Mach1 system has that special R8 collet holder. It's purpose is not only to squeeze the collect down on the tool and not only to provide a reference datum so Z is repeatable. It's alternate purpose is to provide a clean r8 taper surface on the tool. You can see this clearly on the patent illustration:
http://www.google.com/patents?id=8mgWAAAAEBAJ&printsec=abstract&zoom=4
Why is this so important? Because the deformation of the collet as it locks down on the tool really interferes with its ability to make good contact with the R8 taper. If you think of bluing tapers, there is no way in heck that there is much precision in that interface. So now the drawbar force must not only provide sufficient clamping, but it must also combat the reduced surface area and hence friction of the collet in the taper. The Mach1 system avoids all of that.
Folks get started on these air-cylinder only systems because they seem simpler than an impact wrench system. But they're really not unless you're prepared to live with a huge amount of drawbar tension, and even then I wonder how well they are going to work with a facemill or a large silver and deming bit. People keep saying that this has been tried over and over, and it has. The drawbar manufacturers would love a simpler cheaper mechanism, if only one would work. Yet they keep shipping impact wrench based systems for R8, or special patented tricks like Mach1.
What I will tell you is that a rookie machinist can build an impact wrench system in an afternoon and it won't suffer from any of these problems. It can be completely automated for use in an ATC if desired. It's simpler and cheaper. Your biggest challenge for the ATC is that you'll be using solid R8 holders which don't have a standard interface for the ATC carousel. That's no big deal. You'll need to fab some collars for the tooling that serves that purpose. Meanwhile, you will be saving a fortune on TTS holders and you'll have a more rigid system to boot.
Cheers,
BW
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The Mach1 system reveals the secret here. There are really two issues to consider.
First is locking the tool holder to the mill. That's going to be a function of the surface area of the R8 taper and the pull force. I am not too surprised that 600 lbs suffices for that force, even with quite a lot of "work" being done by the spindle.
But there is a second force, and the way it works is hugely counterproductive to the first. That second force is the squeeze on a collet to hold the tool. It doesn't exist with solid tool holders, and it is the reason the Mach1 system has that special R8 collet holder. It's purpose is not only to squeeze the collect down on the tool and not only to provide a reference datum so Z is repeatable. It's alternate purpose is to provide a clean r8 taper surface on the tool. You can see this clearly on the patent illustration:
http://www.google.com/patents?id=8mgWAAAAEBAJ&printsec=abstract&zoom=4
Why is this so important? Because the deformation of the collet as it locks down on the tool really interferes with its ability to make good contact with the R8 taper. If you think of bluing tapers, there is no way in heck that there is much precision in that interface. So now the drawbar force must not only provide sufficient clamping, but it must also combat the reduced surface area and hence friction of the collet in the taper. The Mach1 system avoids all of that.
Folks get started on these air-cylinder only systems because they seem simpler than an impact wrench system. But they're really not unless you're prepared to live with a huge amount of drawbar tension, and even then I wonder how well they are going to work with a facemill or a large silver and deming bit. People keep saying that this has been tried over and over, and it has. The drawbar manufacturers would love a simpler cheaper mechanism, if only one would work. Yet they keep shipping impact wrench based systems for R8, or special patented tricks like Mach1.
What I will tell you is that a rookie machinist can build an impact wrench system in an afternoon and it won't suffer from any of these problems. It can be completely automated for use in an ATC if desired. It's simpler and cheaper. Your biggest challenge for the ATC is that you'll be using solid R8 holders which don't have a standard interface for the ATC carousel. That's no big deal. You'll need to fab some collars for the tooling that serves that purpose. Meanwhile, you will be saving a fortune on TTS holders and you'll have a more rigid system to boot.
Cheers,
BW
Bob,
You seem to "know" things that nobody else seems to know. For example, the required drawbar tension. I looked high and low, and could find *nobody* that could give me anything more concrete than numbers they pulled out of the air. I even asked Tormach - had several e-mail exchanges with several of their engineers, in fact - and THEY have no idea! They asked me to send them any information I come up with! So, I went with what I had, and best guesses, which turned out to be too low. I looked at what Hoss and others did (only 500#, BTW), and assumed I'd need at least twice that, due to the far more aggressive cuts I can take. Even that estimate was too low, by a factor of 2-4. So, had I had a good number at the outset, I never would've gone down this road.
Saving a fortune on Tormach holders? I always planned to make my own, so cost was almost $0. No savings at all there. The commercial drawbars out there are just that - drawbars. I don't think any of them, even the Mach1, are intended for use in an ATC, so it's apples and oranges. Were I after nothing more than a power drawbar, I would've built the impact wrench kind a LONG time ago. It's cheap, simple, and works. But it's *not* well suited to an ATC, which was always my goal.
As for "this has been tried over and over" - I've spent most of my career doing things most others told me could not be done. And, more often than not, I've succeeded. So, for me, the fact that nobody else succeeded is hardly reason to scrap the whole idea, unless I know *why* the others failed. In this case, I did not, so I decided to give it a try and learn for myself. If nothing else, I've learned a few things that I'm sure will come in handy down the road somewhere. And I still believe this approach *can* be made to work, and the cost would not be THAT much more than the impact wrench kind. I can now see good solutions to *all* of the problems., even the high drawbar force requirement. It's now down to whether the additional time, money, and effort to do it is worthwhile, given that I have no shortage of other projects I need to get to. I may well go ahead with something else for now, and complete this in the background. It absolutely CAN be done - I have no doubt of that at this point.
Regards,
Ray L.
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Ray, I'm not the first one to tell you this, and you aren't the first one to try.
But hey, I admire your spirit. Show us how to make it work.
What I haven't heard is why the impact wrench is so poorly suited to an ATC, because it does solve all these problems and is a proven design.
Best,
BW
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What I haven't heard is why the impact wrench is so poorly suited to an ATC, because it does solve all these problems and is a proven design.
Best,
BW
And also works very well, the toolchanger I have aquired for the Beaver mill was originally fitted to a Matchmaker and that uses the impact wrench type power drawbar. When I went to see the toolchanger I was amazed at how well the impact wrench worked, just wish I had taken a vid of it working before the changer was removed.
Hood
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Below is a solution to the release force problem - a very compact and simple mechanical force multiplier. The green housing is stationary (attached to the power drawbar structure) The conical piece is connected directly to the piston of the air cylinder, with the air cylinder pushing straight downward. The cup-shaped part is the plunger that presses on the top of the drawbar to release the tool. The red shows the position when the tool is engaged, the blue when the tool is released. Basically, the air cylinder pushes the conical piece down. This causes the ball bearings to roll along the surface of the conical piece, and at the same time outward along the ramps on the housing. This motion forces the plunger downward. As drawn, this provides a 10:1 mechanical advantage, which means my existing 490# air cylinder would generate almost 5000# of downforce, with 0.150" of travel. The rest of the assembly remains exactly as it is now, with the (now very short - only 2") - guide tube added to the top of the spindle, the same mechanism to prevent that 5000# force from being applied to the spindle bearings, and the same mechanism to "pop" the collet free from the taper.
Regards,
Ray L.
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What I haven't heard is why the impact wrench is so poorly suited to an ATC, because it does solve all these problems and is a proven design.
Best,
BW
And also works very well, the toolchanger I have aquired for the Beaver mill was originally fitted to a Matchmaker and that uses the impact wrench type power drawbar. When I went to see the toolchanger I was amazed at how well the impact wrench worked, just wish I had taken a vid of it working before the changer was removed.
Hood
Hood,
So I assume the alignment pin in the spindle has to be removed? I've always been curious what prevents the drawbar from getting cross-threaded?
Regards,
Ray L.
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The Matchmaker was an Int 40 taper so no alignment screw in that.
I had an Aussie Power Drawbar on my manual Bridgeport years ago, crossthreading never happened in all the years I used it.
Hood
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The Matchmaker was an Int 40 taper so no alignment screw in that.
I had an Aussie Power Drawbar on my manual Bridgeport years ago, crossthreading never happened in all the years I used it.
Hood
Hood,
Oh, I thought you were saying it was R8. Now it makes more sense.
Regards,
Ray L.
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Ray I have used R8 for a LONG time and I NEVER depended on the R8 collet to hold anything(;-) tool creep was always a problem UNLESS you pulled the drawbar like a madman. NOW an R8 toolholder with a collet set was OK as the nut contained the tool quite well.
With a R8 toolholder just a snug up and it was fine. Never really figure out why the R8 collet came about other than just cheap.
Just a thought, (;-) TP
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Ray I have used R8 for a LONG time and I NEVER depended on the R8 collet to hold anything(;-) tool creep was always a problem UNLESS you pulled the drawbar like a madman. NOW an R8 toolholder with a collet set was OK as the nut contained the tool quite well.
With a R8 toolholder just a snug up and it was fine. Never really figure out why the R8 collet came about other than just cheap.
Just a thought, (;-) TP
Terry,
Interesting - For endmills, I've never used anything but collets, and never had one move on me....
Regards,
Ray L.
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OK Now for the $10 story on atc toolchangers with R8 tool holders and a impact drawbar system.
IF you are not rigidly aligned with the small key slot in the R8 a large mess is in the works as if the alignment is off a hair the collet WILL pull up with the key NOT aligned in the slot and cause one heck of a mess. AND it will do it sooner or later (;-) ASK me how I know. I would never use the R8 in an ATC for this reason. THe machine does not know IF the slot is not aligned and there is little room for error.
IF you are going to do a production capable ATC do yourself a favor and find a QC30 spindle with teh center hole for the drawbar. Change out the lugs and fit it with Cat30 holders and a impact drawbar. YES it takes a different drawbar as you have to match the thread in the cat30 holder and it is best to use the splined nut on top. Now you have holders that are more common AND have the slots for the ATC fingers. I have seen this type of arrangement run for years without problems.
Just a thought, (;-) TP
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NOW for the rest of the story (;-) how are you going to index the spindle to the correct position each time. NO easy feat on a BP type machine. The mechanism is quiet simple but fitting it in a manner that works well is not.
Was not a problem with teh tormach style of holders BUT(;-) any style with a keyed holder it is vital.
Just another though, (;-) TP
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NOW for the rest of the story (;-) how are you going to index the spindle to the correct position each time. NO easy feat on a BP type machine. The mechanism is quiet simple but fitting it in a manner that works well is not.
Was not a problem with teh tormach style of holders BUT(;-) any style with a keyed holder it is vital.
Just another though, (;-) TP
Terry,
The short answer is: You don't. You MUST remove the pin from the spindle. I can't for the life of me understand why that pin is there anyway. It serves no useful purpose. If the tool is too loose, it'll just shear the pin off.
Regards,
Ray L.
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It is there for a reason, To hold the toolholder until the drawbar tightens up enough to finish tightening or you run the risk of spinning the holder in the spindle instead of tightening. We tried it without , did not always go well. (;-) Might not be a problem BUT(;-)
(;-) TP
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The dog pin and R8 has been argued over many times on many forums, all I can say is on all Bridgeports I had and any I have seen the pin has been removed and I have never had an issue with a collet spinning whilst tightening the drawbar, both manually and with a power drawbar.
Hood
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This seems similar to this system.
www dot mach-1tooling dot com
I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.
Kenny
Kenny,
I find that system fascinating. The pullstud mechanism is precisely what I had in mind for a future "upgrade" to my setup, and proves that it CAN be done. What really surprises me is the very low drawbar tension - apparently only 600#? After my testing the last few weeks, I'm amazed that's enough to securely hold an endmill in a collet. Do you by any chance have a means of measuring (even crudely) how much torque it takes to make a 1/2" endmill slip in a collet using that setup? I was able to do it by clamping a vise grip on a scrap endmill, and using a $5 hardware store "fish scale" to pull on the handle, then calculate the torque based on the fishscale reading and the length of the vise grip. That would be invaluable in helping me correctly calibrate my drawbar.
I'm going to read their patents and see what I can learn....
Regards,
Ray L.
The reason their system works with such low tension is they are using endmill holders which rely on a set screw that fits in the recess in the side of the endmill, unlike collets they dont rely on friction. The 600lbs of force hold the pull stud fingers up inside a collar. My milltronics uses a spring loaded fingers , marqaurt and a number of other companies have the "gripper" assemblies .
Here is the patent number for an interesting system. 5846037 here is a link to the patent office search page http://patft.uspto.gov/netahtml/PTO/srchnum.htm i attached one of the drawings from the patent below that shows their simple sytem of gripping the pullstud , they use balls wich have a tiny contact surface , some of the finger types have alot more bearing surface
I dont know anybody doing any production work that uses collets over tool holders for the simple reason that you have to measure tool length everytime you change a tool with collets, and the obvious tool slipage problem . The tormach sytem utilizes a collet to hold the tool holders that overcome that one issue but as noted it has limitations and is for light duty use. Expecting to take a 1" depth of cut pass with a half inch endmill may be great as a sales tool but isnt practical in the shop .
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The dog pin and R8 has been argued over many times on many forums, all I can say is on all Bridgeports I had and any I have seen the pin has been removed and I have never had an issue with a collet spinning whilst tightening the drawbar, both manually and with a power drawbar.
Hood
I agree , the pin isnt present in either of mine and we have never had one spin while using the impact type power drawbar, also never had a cross thread or thread stripping issue , although we use tool holders intead of collets so they really dont kneed to be that tight.
Another thought might be to swap to a cat 30 spindle if avail for your machine , I know acra has them for their bridgeport clones and tool holders are fairly cheap
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HOOD were you running the R8 with a ATC or installing them by hand(;-) IF by hand then YOU know IF the toolholder is enganed and tightening up ok you will hold on to the tool holder and FEEL it.
On an atc the machine cannot feel the holder tightening up and can just spin the holder in the spindle. Seen it happen years ago when "WE" were going to perfect and sell the AUTOCHANGE R8 ATC for the BP (;-) LOL
With a bt/ct/nmtb holder the holder is held in the fingers with the index slot so it has a grip on the hoilder that will not allow it to rotate in the finger.(;-)
(;-) TP
Never had a crossthread either(;-) That part always worked well.
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Well, I got some time to catch up on this thread . . . . interesting new ideas presented . . . BUT
We old engineers have a saying "you can't polish a turd"
All of the problems are the result of relying on friction alone to transmit torque. That's the turd.
My original solution is still the best, methinks. Positive drive = end of problem. Easily accomplished with a dog drive on the end of the spindle as I mentioned previously, and since I now see that the plan was to make new tool holders anyway . . zero added cost except for the dog for the spindle nose, which could be a simple bolt-on.
Ultimately, I would prefer Vmax' solution of a new spindle (although I would build it differently) as a rugged and permanent high performance solution, but the current scheme could be made to function, I believe.
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Never had an ATC but I also know I didnt grip them, I normally offered them up with two fingers underneath and certainly never had to stop them roatating, granted if you have crap threads on the collets or the drawbar then it may be a problem.
The matchmaker I referred to earlier had the dogs removed from the spindle nose so that spindle orientation wasnt required so in effect the same as it would be with a R8.
I would however imagine if you were thinking of an ATC with the R8 then it would probably be best to have some form of modification to the holder, the one earlier where a sleeve went over the collet and a nut closed the collet would be very simple to make up and probably get over a lot of problems associated with R8 and ATC. Obviously there will be a patent out so no chance of selling them but cant see anyone being able to do much if you make them for yourself.
Hood
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think a qc30 type spindle could be modified for the claw mechanism and would work just fine. It is ALREADY designed for the machine(lazy me)
I would change the lugs out and go with a cat30 holder to get the grooves for the tool fingers ad ready made toolholders. Then use a mech on top like ray already has built to actuate the drawbar. You would really only need about max 1000 lbs so it is doable with air ( simple)
I have seen a few qc30 spindles on ebay go for cheap.
The rest would be basic mechanical design for the type of ATC you wanted. Get the spindle working and the rest will follow.
(;-) TP
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I just took a peak inside of the qc30 cavity and here is a method that could work using the existing parts and spindle without modifying the spindle. Just add in the claw mech and modify the tool holder a bit. It uses the upper part of the toolholder taper to run the claw(;-)
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pretty far off the original topic of a new power drawbar design , but here is a link to a company that sells the grippers that pull the retention knobs used on cat and bt tool holders. They are avail in a variety of sizes and types
http://www.ortlieb.net/
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I just took a peak inside of the qc30 cavity and here is a method that could work using the existing parts and spindle without modifying the spindle. Just add in the claw mech and modify the tool holder a bit. It uses the upper part of the toolholder taper to run the claw(;-)
If you look back to the photos in Hood's reply #49, this is exactly how his power drawbar works.
Positive drive is the key whether by going with a new CAT spindle or modifying the R8. Either has product potential, methinks. The fast track solution would be a simple modification of the Tormach setup, but in the long run, of all the ideas presented, your spindle solution I think would offer the best perfrormance, and you only have to produce and/or modify one part. The rest are proven off-the-shelf items purpose built for the application.
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THere may be a way (;-) to do a claw type AND use the tormach style holders using a R8 collet adaptor that has a couple of MODs. The tormach style would need a stud added to the top and the claw would live inside the R8 adaptor and would work from the drawbar and RAYS mech would operate the drawbar on top.
(;-) TP
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Ray LOOKS good. Here is something to consider. The piece that holds UP on the spring pack, the lower plate with the finger that slides under the pack. THis will be tricky to get the spindle in the exact position so the lever can slide under the pack AND still not have any play. ANY PLAY will cause the spindle bearings to load up as the pack is compressed. You might want to consider a push me pull me type of compressor arrangement that floats and as it is compressed both sides of the PACK are compressed at the same time. AND it puts zero load on the drawbar.
Another thought when building a drawbar is the machines always use a long 30deg angle tool holder that does NOT require any of the force of holding in the toolholder to be used to HOLD the bit as well. (;-)
Just a thought, (;-) TP
indeed it would be nice to see that, cylinder incorporated with bolted to base sviwel flange and fork clevis joining with drawbar, both strokes driven using 5/2 1/4" solenoid valve with exhaust regulators, micro plc with hmi is awesome for sorting out things like limits, rpm encoder, safety relay circuit, coolant, ..... its so obvious that tapered shanks dont need holding force :) anyhow... the cylinder is not pressurised both sides simultaniously!!, 5/2 solenoid valve principle of work clearly indicate its impossible, thats why right stroke here is very important, you can always adjust it winding the clewis onto the rod bit more and properly set up cylinder's cushions you could have, i wonder if it would be possible to drive using 2 Oz carbon dioxide inserts and pressure regulator to eliminate compressor, anyhow i think that you've done an exceptionally good job, ... .. one more... cylinder fitted with reed swith could eliminate any hazards related, micro plc should also controll mains contactor
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Hi Ray,
I enjoyed reading about your ATC. I'm curious on how it's preforming? I'm looking into building one for my cnc Bridgeport.
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Hi Ray,
I enjoyed reading about your ATC. I'm curious on how it's preforming? I'm looking into building one for my cnc Bridgeport.
It isn't.... Never could get it to develop enough force to adequately retain the Tormach holders - over 2000# of drawbar tension is required for maximum retention. The only practical way to achieve that is with an air over hydraulic system, or a large diameter, multi-stack air cylinder. The other approach i'd love to try is using a stepper motor, driving a high reduction planetary gearbox to directly spin the drawbar. This would allow the driawbar to be fully tightened to any desired torque, loosened a controlled about to enable using Tormach tool holders, or the tool released completely. It's mechanically very simple as well. You'd want to be able to generate 20-25 foot-lbs for tightening, and about twice that for loosening.
Regards,
Ray L.
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Sorry to hear this Ray. When I'm using an end mill I typically only take of .030-.040 per pass. After reading through the post it sounds like you possibly taking quite a bit deeper cuts. Would your ATC work with the shallow passes that I'm taking? Thanks again.
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Sorry to hear this Ray. When I'm using an end mill I typically only take of .030-.040 per pass. After reading through the post it sounds like you possibly taking quite a bit deeper cuts. Would your ATC work with the shallow passes that I'm taking? Thanks again.
Yes, for a small machine, taking light cuts, a great deal less force is required. 1000# is not terribly difficult to achieve, and is adequate for most benchtop-class machines, or light-duty work. I was doing low-volume production work, so needed to be aggressive to get reasonable throughput - my typical roughing pass is up to 1/2" deep with a 1/2" endmill, so keeping the tool where it belongs is pretty important....
Regards,
Ray L.
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Thanks again Ray! I think I will give it a try. Do you have plans available for your design or for sale? I don't know how to keep the disc springs from applying force on the on the bearings. That is my main concern for starting this project.
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I have a partial set of drawings, but they would require some "interpretation" to be intelligible. The really hard part is containing the bellevilles, and keeping them, and their container, concentric and balanced. I never did quite accomplish that, which is another reason to abandon that approach. Honestly, I would look into the stepper/planetary gear solution. I think it's simpler, more flexible, and presents fewer difficult design challenges.
Regards,
Ray L.
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Hello Ray:
Are you familiar with the "Universal Houdaille Kwik-Switch 200" tool holder, and BP spindle replacement?
I have two of them; one is installed on a manual BP clone, and the other is on a large Lagun mill, 40 taper spindle, with CNC. You can change tools by hand (no wrench required) in about 6 or 8 seconds. The spindle must have a brake, and you can change the tool holder with one hand.
My third mill is a bed-type CNC with a 16 pocket carousel tool changer. The tool holders are BT-40. Back when I bought tooling for that mill, 1990, I was able to get BT-40 tool holders with the Universal Houdaille collet taper bore/lock nut arrangement. This enables me to utilize the same collets and nuts on all three machines.
Of course, you get absolute repeatable Z axis offsets for all your tools.
The tool holders are positive drive with two drive tangs on the body, and they have three style collets.
(1)Acra-flex, which has a small range in tool shank diameter
(2)Acra-mill super high precision, which takes the exact tool diameter without an internal drive plug.
(3)Acra-grip, same style and precision as (2), but has a spring-loaded plug, which drops into the mill cutter flat giving a positive, no-slip drive to the end mill for heavy milling.
The down side to all this is, Universal Houdaille went out of business back in the 80's, due to the insane Wall St. leveraged buy-out swindle (Investment bankers call it good business!).
There are companies making collets and other parts. There are also new and used Universal Houdaille collets and parts on E-bay.
I just looked on E-bay, and they have a good condition BP clone spindle for sale, and loads of collets, and tool holders.
I consider changing over to the Kwik-switch 200 system one of my best investments in tooling.
Regards,
John
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Hey Ray,
This is exactly the issues I ran into when I was doing a prototype ATC for tormach waayy back......
I was asked on the cnczone that my holder had to be able to hold an r-8 with it doing a 1" DOC with a 1/2" roughing endmill though AL.......... "Like thier vids show for thier NON-atc machines doing....." They where unwilling to invest the capital needed to get the ATC to that level, and they wanted me to keep the price under 3k......... it is funny almost 3 years later they come out with an ATC/Draw bar that cost far, far more than that........ and I STILL have not seen that machine cut the 1" AL bar like I was asked to do....
scott
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Take a look at the work Dave Decaussin has doon with the R8 spindles and an ATC with claw release. He uses a modified version the cat30 holder.
There are some vids on YouTUbe
(;-) TP
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Ray, so I have a Bimba 4" bore, 4" stroke, single-stage, max force 1256 lbs @ 100psi. The machine is a Sieg SX-3, and the application is light one-off project/prototype work. Is it worth trying this set-up first directly acting, without a lever, then moving to the z-bot/hoss approach if this is insufficient? Or, do you know already that it is not workable at 1256psi?
Thx!