Messages

341

General Mach Discussion / Re: keranla Speed & Mach locking up

« on: May 27, 2012, 11:40:16 PM »

Keep in mind there is absolutely NO BENEFIT WHATSOEVER to setting your kernel speed any higher than the minimum necessary to achieve your desired rapid speed.

Regards,
Ray L.

342

General Mach Discussion / Re: A Power Drawbar Like No Other....

« 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.

343

General Mach Discussion / Re: A Power Drawbar Like No Other....

« 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.

344

General Mach Discussion / Re: A Power Drawbar Like No Other....

« 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.

345

General Mach Discussion / Re: A Power Drawbar Like No Other....

« on: May 16, 2012, 06:52:44 PM »

You tried making your own gripper using Dave DeC's drawings, didn't you?  Or am I confusing you with someone else.

Nope, wasn't me. I can make one easy enough, but then it needs to be hardened and there are not too many shops that will harden one item for anything approaching a reasonable cost . .  and I can't  blame them.  I can get stuff nitrided by just 'riding the tailgate' when they are doing other stuff, but not precision hardening and tempering.

And a Belleville drawbar is a really tough thing to do on a converted knee mill....

I've watched a few of these PDB projects and they all seem to suffer from the same problem . . .  I hasten to say 'in my opinion'. The bellevilles are not the problem. Early on I noticed that people had no idea how much force to use. Then if someone did discover a target force, they were unable to figure our how to generate enough force to release it.

A pneumatic PDB is very doable, even with R8, that's not why I switched over. A PDB is a stepping stone to an ATC, otherwise, not enough benefit for the effort, again in my opinion. I can find no way to make an unattended, reliable, ATC with R8, and I've looked at it a bunch of ways and studied a lot of different approaches currently out there . .  including Tormac's stuff. Tormac's is workable, but has disadvantages, starting with the old R8 problem of needing gobs of force to retain and turn the toolholder. BT30 is short, only needs a few hundred pounds to retain the holder because the torque transfer is taken by dogs and not friction.

 

It hjas been pretty well established at this point that to use TTS to its full capability (which I do every day), requires upwards of 2500# drawbar tension, or 25+ ft-lbs drawbar torque.  That's hard to achieve without a really large pneumatic cylinder, a multiple-piston cylinder, or an air over hydraulic system.  Then there's the headache of packaging on a knee mill, where the Bellevilles either have to fit inside the spindle, or you need to build some kind of holder for them above the head, which is a major PITA.  Hence my decision not to go that way.

Are you sure a few hundred pounds is adequate for BT30?  Sounds low to me.  I know ISO30 requires on the order of 1300#, and I would've thought BT30 would be the same.  I think the issue is not so much torque capability, but loss of rigidity caused by un-seating of the taper, due to the holder being pulled down due to cutting forces, and leverage through the tool holder and tool holder to spindle interface.  I have seen the spec for ISO30, but not BT30.  I would not think the drive dogs would be of any real value until you get up into the 5-10 HP range.

Regards,
Ray L.

346

General Mach Discussion / Re: A Power Drawbar Like No Other....

« on: May 16, 2012, 04:24:15 PM »

Interesting arrangement. Proving the old addage 'more than one way to skin a cat'.

Being one of the guys with a 'toe in the water' on this topic, I have a box of parts waiting for me to find the time to put together my own PDB. I am taking an entirely differnet approach (BT30) and what has me backed up is the cost of drawbar collets; $400 to $500 US.  Ouchies. 

Many moons ago I had a furnace and did my own heat treating. I may have to go back to that in order to be able to make some of the parts I want . . . or . . . I could just stop  and spend the money and get on with it.

You tried making your own gripper using Dave DeC's drawings, didn't you?  Or am I confusing you with someone else.

I would like to eventually change to ISO30, but since I do 99% of my work with TTS, this is a nice intermediate step.  And a Belleville drawbar is a really tough thing to do on a converted knee mill....

Regards,
Ray L.

347

General Mach Discussion / Re: A Power Drawbar Like No Other....

« on: May 16, 2012, 04:22:14 PM »

Pretty neat Ray, nice concept.
One question ... When tightening, do you run the motor for a specific time to assure proper tightening and let the motor stall ? ? or are you sensing the load as an input to Mach ?

Thanks,
Russ

Russ,

Right now, I have only partially implemented software to drive it, so I'm taking a brute-force approach - To loosen, I command a move equivalent to 1.25 turns of the drawbar.  To tighten, I command a move equivalent to 1.5 turns of the drawbar, ensuring the motor will stall before it goes that far.  Seems to work just fine like that - I've been using it all day today without a single hiccup (well, other than Mach3 weirding out one me twice....).  When I move it over to the KFlop, and ditch Mach3 (Mach3 is currently running ONLY the drawbar, everything else is running on the KFlop), I will put an encoder on the stepper, so I can detect when the drawbar stops moving, and stop the stepper right there.

Regards,
Ray L.

348

General Mach Discussion / Re: A Power Drawbar Like No Other....

« on: May 15, 2012, 12:33:34 AM »

Nice craftsmanship, Ray.

Thanks, Sam!  I'm really pleased with how it came out, and how easy it was!

Regards,
Ray L.

349

General Mach Discussion / Re: A Power Drawbar Like No Other....

« on: May 14, 2012, 06:01:05 PM »

Well, I'm happy to report the power drawbar seems to work *perfectly*!  I got it all plumbed and wired, and did the 20 or so lines of macro code to make it work, and it grabbed, and released, the tools 25-30 times in a row, without so much as a single hiccup!  Limiting current when tightening seems to work perfectly, tightening the drawbar very consistently, and no problems whatsoever loosening it again with max current.  This is going to be REALLY nice, and gets me one giant step closer to an ATC!

Regards,
Ray L.

350

General Mach Discussion / Re: G31 command.

« on: May 14, 2012, 10:55:33 AM »

FWIW - I did have problems with G31 with the SmoothStepper.  I think most/all of these problems were eventually resolved, but there were times when it would do just plain bizarre things - like moving opposite the commanded direction, moving the wrong axis, moving the wrong speed, even moving multiple axes.  This cost me more than a few probes (I was using rigid probes).  But, then, I seemed to be plagued with all kinds of problems that nobody else had.  Happily, since switching to a KFLop, and my own custom CNC controller app, I haven't had one single problem of any kind, and the whole system has become dead reliable.

Regards,
Ray L.