Messages

1111

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

« on: June 22, 2009, 12:40:59 PM »

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

« on: June 22, 2009, 09:38:51 AM »

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

« on: June 21, 2009, 04:07:33 PM »

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

« on: June 21, 2009, 09:08:37 AM »

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

« on: June 20, 2009, 04:42:57 AM »

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  project.

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General Mach Discussion / Re: couple of things I have noticed with mach /g83 problem

« on: June 20, 2009, 03:18:55 AM »

Macros in Mach are VB scripts. Mach has the editor built in.

From the top line of the standard Mach screen:

Operator>VB Scipt Editor

I ran into a problem thinking I could explicitly pick up an external subroutine from wherever it was located, but Mach is adamant about where they are, so it might be a safe assumption that all of Mach is sensitive to placement of external references. So make sure you have your macros in the proper subdirectory (folder) and that there are not more that one version floating around with the same filename.

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Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: June 20, 2009, 02:53:56 AM »

Bead blasting is for delicate stuff. I just use fine sand and then coat with a product from Eastwood called satin clear for bare metal. There is not a lot of paint that will stick directly to aluminum. This is an amazing product  . . expensive though. 'Self-etching' or otherwise 'stick to bare metal' products are caustic (have acid in them)  . . . .  VERY nasty stuff . . respirator only, please!


As to the G-code, it calls a few other macros and internal subs and uses a lot of variables within the code itself so it will be very difficult to decipher without a lot of proper commenting.

I used to program a lot . . . 25 years ago . . and I was sloppy even then about commenting programs. A well deserved criticism I would get from colleagues was that my programs were difficult if not impossible to maintain because I would do very complex things and not explain what I was doing or how. I often could not even go back and figure out WTF I had done 

If I can get time to comment the code sufficiently for it to be understood and maintained in some reasonable way, I'll make it available individually for those who may want to peruse. I do not have time to answer a lot of questions about it though.

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General Mach Discussion / Re: Limitations of PC Parrallel Port

« on: June 19, 2009, 02:16:31 PM »

I can point you to a feature in Mach that you will then need to study up on and experiment with.

The CV feature does have some controls that you have access to for tailoring the behavior for specific needs/jobs. I am no expert in these settings and while I have been known to occasionally cut the cheese, I don't cut wood so I'll have no specific advice for you.

You can define within CV, as I recall,  at what angle the CV will disengage. With this control, theoretically, you can have CV active to avoid the shaky movements that Hood described while still having the ability to, within reason, keep your corners sharp.

I cut a lot of aluminum with small (sub 3/8") end mills at 7,000 RPM so I have similar concerns to people cutting wood at say 20,000 or more, and thus far I have only encountered on precision shaped pocket that required expressly invoking exact stop mode.

CV does not round off corners randomly. Is is proportional to the feedrate. Sort of like driving your car; the faster you are travelling, the sooner you need to start turning and the arc you can sustain is going to be bigger the faster you are going. So IF you are not able to obtain a completely satisfactory result with the CV controls, you can still 'tune' a particular cut by slowing down the feed rate with a proportional reduction in spindle speed to prevent burning at problem spots in the process.

The above is not an ideal solution, but then again there is no logic in dissecting too closely a problem that may not even exist, so as Hood suggested, there is a time to talk and a time to just get in there and see what she'll do for you. Methinks you are at the latter.

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General Mach Discussion / Re: Limitations of PC Parrallel Port

« on: June 19, 2009, 05:43:15 AM »

Thanks for the reply simpson36!  You confirmed my guess about the pulse rate.

As for the acceleration, I need to ask again.  I am familiar with the concept of "work hardening" from my machinist days (years ago).  I should have given more information or asked the question differently.  I will mainly be cutting wood (pool cue inlays) and the occasional piece of plastic or aluminum (fixtures/jigs).  I'm not a production shop, so cycle time is not my main concern.  I'm more concerned with the hightest level of accuracy and longest life (least wear-and-tear) I can obtain with the machine. My question about acceleration was more "what's best for the machine".  Could too slow an acceleration perhaps actually be bad for the motors?

I'm not an electron guy, so that question is outside my knowledge, but I can think if no reason slow accelleration would hurt the motors. My understanding is that Steppers draw full current all the time so it would have no practical effect on those motors, and a servo motor would simply draw less current to accellerate the load more slowly, so theoretically it would run a little cooler. I don't think this is significant though.

While wood, plastic and most aluminum will not work harden on you, wood will definately burn and plastic will melt if you loose your feed rate. Softer grades of aluminum will often cling to and clog the tool bit if it gets too hot, so I would still go with the fastest accelleration the motors can reliably tollerate in order to achive the most consistent feed rate.

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General Mach Discussion / Re: Parallel port for PCI bus that works with Mach3 - just passing along info

« on: June 19, 2009, 05:27:15 AM »

You are very welcome.

Since I posted the info, I have discovered that although for me 90% of the time the second port (ribbon cable) was assigned LPT2, the physical ports on the card are not locked in any order and either can be assigned LPT2 or LPT3.

To get the addresses, follow this sequece:

Start>Control Panel>System>Hardware>Device Manager>Ports>Printer Port>Resources

What you seek is the first hex address given for LPT2 and for LPT3. For the port physically on the card, give Mach3 the address shown for LPT3 (that's USUALLY what it is). If that does not work, then just try the address for LPT2 and it should spring to life.