Power Drawbar Help Please

I've been messing with my power drawbar now for a couple weeks and can't seem to get it to work consistently. Here's my problem, when i get the drawbar tightened to the point where the tool has no pull out during machining, the drawbar releases the tool fine before i machine anything but once i do the littlest amount of machining , the tool then will not release.

I've tried using different pound washers, stacking them in series and parallel, different amount of cylinder stoke to compress springs, i've tried lubricating the drawbar components according to Tormach's website and un-lubricated, different air pressures, not sure what else to try

any ideas? It's a floating plate design on a LMS x2

any help is greatly appreciated
Thanks
kyle

Hi
You know, detailed pixs are worth 10,000 words. If you can take several detailed pictures and post here maybe someone can see what the problem is. Several members here have PDB's that works.
CH

Getting a Belleville drawbar to release reliably requires several things:

1) Sufficient compression of the spring stack - this typically needs to be about 0.05" more than required to get it to release once.
2) Sufficient down-force on the spindle to get the collet "popped" free from the taper. For R8, this is typically on the order of 100 pounds.
3) A clean, dry tool shank and collet bore, and a clean, lightly-lubricated (with anti-sieze paste) collet taper. You need to clean and lubricate every few weeks to keep it working reliably.

I've seen some PDB designs that put ALL the force on the spring pack, and none on the spindle, which I would expect to be less than totally unreliable. The down-force can be easily generated by fairly springs that press down on the plate that supports the air cylinder, so as the air cylinder lifts up, those springs are compressed, applying a controlled down-force of 50-100 pounds through the drawbar to pop the collet free. The amount of force required will be largely a function of the Belleville spring force.

Regards,
Ray L.

I actually took the whole assembly off and just used the Belleville washers to see if it would hold and I tried different compressions and then finally went and tightened them all the way to flat so that's over 1000 pounds and the tool still pulled out. I'm beginning to think that maybe the spindle itself has an improper taper to match the R8 taper. Or friction somewhere, however I don't think there's much left for friction...

Are you sure your threaded rod isnt extending too far into the collet? Something just doesnt sound right. You shouldnt be experiencing pull out especially with an X2.

Pics?

I use Hoss' MAD or manual drawbar release, same belleville stack ()()()() and I never experience pull out or have issues with release.

Something is wrong with your drawbar, spindle, or collet. 1000 pounds is almost 2X what you require for an X2. If you're getting pullout, that 1000 pounds is NOT being transmitted properly to the collet. Remove the Bellevilles, and replace them with flat washers or a hard spacer. Can you then tighten the drawbar enough to NOT get pullout? I'm guessing you'll find you can't, which means something is preventing the collet from pulling far enough up into the spindle to close fully.

Regards,
Ray L.

Quote:

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Originally Posted by SCzEngrgGroup

Something is wrong with your drawbar, spindle, or collet. 1000 pounds is almost 2X what you require for an X2. If you're getting pullout, that 1000 pounds is NOT being transmitted properly to the collet. Remove the Bellevilles, and replace them with flat washers or a hard spacer. Can you then tighten the drawbar enough to NOT get pullout? I'm guessing you'll find you can't, which means something is preventing the collet from pulling far enough up into the spindle to close fully.

Regards,
Ray L.

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Good call Ray, I never thought to try the washer/spacer thing. Makes sense. I've tried with the stock drawbar plus different length bolts as drawbars and all had the same results. If I tried just a hard spacer it would definitely isolate the problem. However I'm almost positive at this point it's the spindle or collet. I have a new collet that will be here in a few days. If that isn't it, I guess next and only place left is the spindle. Before I started using the TTS system, I never had a problem. And it's not like I can put 1000 pounds of pressure on the spindle by hand.

Your cutter isn't squealing while cutting is it? A high pitch squeal can cause enough high frequency vibration that it will allow your cutter to pull out. I've had this happen a few times with a particular three flute cutter.
Eric

I think you should check properly the stroke of cylinder and if necessary you should check this post

http://cncmachinetools.org/collet-dr...nsert-problem/

Are you using an actual TTS collet or a 3/4" collet?

I'm using an actual TTS collet. I actually had a TTS end mill holder pull out a little last night and I am not using the power drawbar for the time being. I'm beginning to think it's the TTS collet that is the problem. I should have a new one tomorrow. Hopefully that will solve the problem. I have far too much money invested in TTS tooling for this to be happening

First, try a regular 3/4" R8 collet. - it won't give you Z repeatability, but it will otherwise work fine. If that works ok, then your TTS collet is clearly defective. Is it a real Tormach collet, or one of the Chinese knock-offs?

Regards,
Ray L.

BTW - One common problem on these machines is the "index" set-screw in the spindle is often set too deep, or is too large in diameter, and binds in the slot along the side of the collet. Sometimes the collet slot it too shallow, or too narrow as well. You should loosen or remove that screw, and see if it changes anything.

Regards,
Ray L.

it's a real TTS collet, new one just got delivered. i'll check the set screw and new collet tonight hopefully

Thanks
kyle

Quote:

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Originally Posted by SCzEngrgGroup

BTW - One common problem on these machines is the "index" set-screw in the spindle is often set too deep, or is too large in diameter, and binds in the slot along the side of the collet. Sometimes the collet slot it too shallow, or too narrow as well. You should loosen or remove that screw, and see if it changes anything.

Regards,
Ray L.

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Ray,
i tried my new TTS colleta and still the same problem. the index pin doesnt look to be a set screw, maybe pressed in? any idea how to get it out? i dont want to start trying to pound it out in fear that i might damage something

Thanks
Kyle

Quote:

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Originally Posted by cadguy247

Ray,
i tried my new TTS colleta and still the same problem. the index pin doesnt look to be a set screw, maybe pressed in? any idea how to get it out? i dont want to start trying to pound it out in fear that i might damage something

Thanks
Kyle

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I've never seen a spindle where it wasn't a screw. What do you thin it's not? Can you see the hole on the outside of the spindle? It MUST be inserted from the outside. Perhaps get in there with a file and shorten it?

If you put some Kyken on the collet, can you see where the pin is scraping it?

Regards,
Ray L.

It's definetly not a set screw, there's no hex, or slot for a screw driver. the pin itself is larger in diameter on the outside and smaller inside, must be pressed in from the outside. i think i will try to drill a small hole in it and use an ez-out to try and twist it out. might be hard to do though because the center of the pin is just above the bottom of the spindle housing making it tough to get a drill or ez-out in the center of it

Quote:

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Originally Posted by cadguy247

It's definetly not a set screw, there's no hex, or slot for a screw driver. the pin itself is larger in diameter on the outside and smaller inside, must be pressed in from the outside. i think i will try to drill a small hole in it and use an ez-out to try and twist it out. might be hard to do though because the center of the pin is just above the bottom of the spindle housing making it tough to get a drill or ez-out in the center of it

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I would suggest just drilling it out, and replacing it with a set-screw with the tip turned down to the right diameter to fit the slot in the collet. Use blue Loctite to keep it in place.