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1121

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 12:35:08 PM »

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.

1122

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 28, 2009, 09:53:08 AM »

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.

1123

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 27, 2009, 06:26:49 PM »

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.

1124

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 27, 2009, 04:13:10 PM »

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.

1125

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 27, 2009, 12:48:21 AM »

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.

1126

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 26, 2009, 08:22:07 PM »

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.

1127

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 26, 2009, 07:34:53 PM »

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.

1128

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 26, 2009, 07:24:16 PM »

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.

1129

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 26, 2009, 05:26:51 PM »

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.

1130

Show"N"Tell ( Your Machines) / Re: What The World's Been Waiting For - Yet Another Power Drawbar Design

« on: June 25, 2009, 05:15:00 PM »

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.