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Author Topic: A Power Drawbar Like No Other....  (Read 15603 times)

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Offline BR549

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Re: A Power Drawbar Like No Other....
« Reply #20 on: May 17, 2012, 05:32:48 PM »
Steve here is the original You TUbe that started it all(;-). Dave Dec is a sharp cookie.

http://www.youtube.com/watch?v=l2PWuqgviS8&feature=relmfu

He went on to produce his OWN new version of a scratch built Mini CNC machine center the UMC10

(;-) TP
« Last Edit: May 17, 2012, 05:34:20 PM by BR549 »
Re: A Power Drawbar Like No Other....
« Reply #21 on: May 17, 2012, 08:05:28 PM »
The motor driven drawbar idea has been around for a while as well as the impact method. The motor idea never survived for various reasons. But the impact version is still active.

The standard kneemill with the reduction gearbox on top of the spindle is a bear to get a auto drawbar working dependably. OTHER than the impact method AND that is NOT with R8 collect but with R8 solid toolholders.

After two full days, mine is still working perfectly, and I am VERY pleased with it.  Soooooooooo much nicer than the execrable impact wrench drawbar....

Regards,
Ray L.
Regards,
Ray L.

Offline simpson36

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Re: A Power Drawbar Like No Other....
« Reply #22 on: May 18, 2012, 08:50:23 AM »
"Torque is not an accurate way to determene the amount of stretch. Yes it acan get you into the ballpark(;-)"

We don't agree completely on how to get here, but in this statement, we agree completely. In my youth, I raced. Part of racing is building motors. Rod bolts are arguably THE most critical fastener on the motor and while most people (as well as all OEM) are satisfied with using a torque wrench, they do not work well with UBER strength bolts form ARP or equiv (if I remeber that brand correctly). We used a stretch gage to measure the actual stretch on the bolt. Still using a torque wrench (the old beam type), to turn the nuts, you could still see the torque being applied when you reached the correct stretch. THat will make a beliver out of the worst skeptic (usually I fill that role :-)) However, a lot of rods used cap screws, so it was back to the trusty torque wrench for that. 

OK, enough remenising, back to the debate; I get the part about holding on to a cutter with a collet vs holder, but you ahve not addresssed my comment on transferring the torque from the spindle to the taper, which is done by friction alone on R8 . .  as to the pin? Don't even go there. Many people remove it.

One more comment and I'll leave you alone. It seems curious that one would re-grind every CAT holder instead of regrinding the spindle? Perhaps that will come clear when I get the link. I reground my R8 spindle to BT30 no sweat . .  in fact it is due for a touch up.

Offline simpson36

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Re: A Power Drawbar Like No Other....
« Reply #23 on: May 18, 2012, 09:08:27 AM »
Steve here is the original You TUbe that started it all(;-). Dave Dec is a sharp cookie.

http://www.youtube.com/watch?v=l2PWuqgviS8&feature=relmfu

He went on to produce his OWN new version of a scratch built Mini CNC machine center the UMC10

Thanks for that link!  As soon as he said the word 'prototype' I understood why modify the holders instead of the spindle. I will check out his other vids when I get a chance.

Very nice machine, I must say. Of the pieces of the puzzle, I have the BT30 spindle, the multi piston Pneumatic cylinder, The wrong Bellevilles (they are sized for R8 . .  way too big), and most importantly, as repeated numerous times by Dave, indexing on the spindle.

My spindle is a big DC servo motor and I have on my desk the newest member of Copley's AccelNet drive series. Jumping up from a 10A PWM to this 30A servo drive will be quite a nice change. Hard tapping, here I come!

Now for the problem child; the drawbar collet . . .  last night I purchased a furnace to do my own heat treating again. Lots of new possibilities open up . . . including making my own 4th axis spindles . . 

The last piece of the puzzle will be the hardest one to find . . . .time. 

Offline BR549

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Re: A Power Drawbar Like No Other....
« Reply #24 on: May 18, 2012, 09:14:54 AM »
ON the important stuf you preset the bolt with a torque wrench to a low point just to take up the slack. Then rotate the bolts a set DEG of rotation until you have turn the bolt the Prescribed amount. Rods Mains Heads are the important stuf(;-)

YES friction is what holds the R8 holder in place.

The idea on Daves Catr8 was it is EASIER to buy a premade toolholder over removing the spindle shipping it out and then grinding the spindle and reassy the spindle.  He used a standard Grizzly unit in his prototype machine. ALSO using the SHORT CatR8 holder gives you a little more room in the spindle for the Gripper and pull stud assy.

Just a thought, (;-)TP

Offline simpson36

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Re: A Power Drawbar Like No Other....
« Reply #25 on: May 18, 2012, 09:41:13 AM »
ON the important stuf you preset the bolt with a torque wrench to a low point just to take up the slack. Then rotate the bolts a set DEG of rotation until you have turn the bolt the Prescribed amount. Rods Mains Heads are the important stuf(;-)

That is a great technique to use if you have the stretch spec and do not have access to both ends of the bolt.

Quote
YES friction is what holds the R8 holder in place.

It's biggest drawback, methinks. Same goes for Tormach's setup. They are short and ATC-able, the newer ones have a groove for holding on to them, but still rely on friction . . . and are even worse in that regard than R8. . . . . probably going to hear from Ray on that comment  >:(
Re: A Power Drawbar Like No Other....
« Reply #26 on: May 18, 2012, 10:04:19 AM »
It's biggest drawback, methinks. Same goes for Tormach's setup. They are short and ATC-able, the newer ones have a groove for holding on to them, but still rely on friction . . . and are even worse in that regard than R8. . . . . probably going to hear from Ray on that comment  >:(

Depends what you're trying to accomplish.  TTS is great, for what it is, and I think Tormach is very clear about what it is, and is not.  For small machines (probably no more than 2-3HP max), they work great.  I''ve been using them on my 4HP knee mill for 3 years, and never had a problem.  And, in reality, most hobby machines (my BP clone included) run out of either power or rigidity before they tax the limit of TTS capability.  But for your 7HP spindle, it would be totally inadequate.  I believe the taper in R8/ISO30/BT30/CAT30 is quite adequate up to perhaps 5HP, which seems to me about the limit for what you can do with any tool that will fit in a 30-taper holder, no?  For something in the 7-10HP range, I would think you'd want to go to 40 or 50 taper, like the big boys do.

Regards,
Ray L.
Regards,
Ray L.

Offline BR549

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Re: A Power Drawbar Like No Other....
« Reply #27 on: May 18, 2012, 10:42:08 AM »
To me the TTS is usefull I guess but it suffers all the problems that a R8 collet has holding the tool. Its only real advantage over 30 series is it is cheap(tool holder)  and doable on a standard R8 machine(cheaper as well).

(;-) TP

Offline simpson36

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Re: A Power Drawbar Like No Other....
« Reply #28 on: May 18, 2012, 11:09:06 AM »
Nice job on your PDB, Ray. Will have my furnace next week. Need to do more homework to decide between ball type catch or the 'finger' collet to grab that little BT30. Not looking forward to cutting tool steel again.

Total agreement here with both Himmy and BR assessments of TTS.

Since full agreement does not make for a particularly intersting discussion, I'll go earn a living now.

Nice chatting with all of you again.

- Steve
Re: A Power Drawbar Like No Other....
« Reply #29 on: May 25, 2012, 04:56:54 PM »
Just an update, now that I've got quite a few miles on the PDB - I absolutely LOVE it! Other than the quill drive, probably about the best thing I've done for this machine.  Over the last several weeks the PDB has proven to be bullet-proof.  A few days ago, I did the necessary re-wiring to get it running on the KFlop, under my controller app, instead of running under Mach3.  This has enabled me to speed it up considerably, since I'm no longer limited by parallel port and "kernel" speed.  That allowed me to triple the speed, with no loss of reliability, and I suspect I could go further still, just haven't had the time to try.  But, I can now do a complete manual tool change in under 4 seconds, and it has not misbehaved once in hundreds of changes.  It does a wonderful job of very consistently torquing the drawbar, and it has never once failed to engage or disengage, loosen the tool, or pop the collet free.  It's also FAR quieter than those hideous impact wrench PDBs.  This was a little bit on the expensive side, due mostly to the $150 gearbox, but it was dead simple to build (I could easily build one now in about half a day), and it was absolutely worth every penny.  And, it should work, unchanged, when I finally get around to swapping out my R8 spindle for an ISO30 spindle.

Now I can finally get to work on a real tool-changer!

Regards,
Ray L.
Regards,
Ray L.