Power Drawbar Getting Stuck

I have been using a pneumatic power drawbar for about 6 months. I purchased it from Priest Tools. It uses a ram to press against a stack of Belville washers that pull up on the drawbar. The drawbar is connected to an Tormach/Lyndex R8 collet that I use for TTS tooling. For the most part it works great.

I have had a problem a few times when I don’t use the machine for a few weeks and find that the R8 collet sticks and won’t release. To make sure there are no tiny burrs, I very lightly wet sanded the collet and spindle with 2000 paper. I then re-apply anti-seize to the collet and all was good. It worked better than ever!

It worked great for a few months, then I did not use the machine for 3+ weeks and once again it was stuck when tried to use it.

I examined the inside of the spindle and could see some marks where the slots in the R8 collet have been rubbing against the inside of the spindle (Please see below). There are marks like this for each of the three slots on the R8 collet. Does this look normal? If not, any idea as to how to stop these from happening? Better yet… any idea as to how to stop this thing from getting stuck?

Sorry I missed your post. Perhaps unrelated, but the problem I had with the drawbar was with the set screw inside the spindle the keeps the collet from spinning. Too tight and the collet won’t release, but if it is too loose, then during a heavy cut it will skip over the slot and deform the collet. My damage collet then left a similar mark on the inside of my spindle.

Since it has been several months, let me know if you discovered a different cause of this issue besides the one I mentioned.

Sorry for the late reply. For some reason I do not get a message when someone responds to my posts. The problem I am having is difficult to resolve. The drawbar will work perfectly for some time, and other times it gets stuck. Precision Matthews told me that this is typically caused because the top of the spindle of the PM833 is machined too small. They recommend making a dowel with fine sandpaper on the end of it, run the mill as slow speed and open up the top of the spindle a bit. I have been reluctant to do this.

I am going to try using grease instead of anti-seize on the top portion of the collet the next time this thing freezes up. Right now, it is working fine. If all else fails, I will try opening up the top portion of the spindle.

Thanks… Richard

Well that is a bit of a disappointing response from a precision tool reseller. How did the grease fare?

on a commercial machining center they put an oiler on the air line and the flow rate can be adjusted so every time a tool change takes place the spindle gets a shot of oil. oil is something that is always added to the system so without an automatic oiling system having to grease things up every so often is something that is going to have to be done from time to time. so once you figure out how often you just need to get in the habit of making time do it on a regular basis. i would think grease would last a bit longer taking a guess.

Thanks Jay. Funny, I spoke in depth with Greg from Priest tools who sold me the power draw bar. He said he never has to reapply anti seize and these things usually work for years with no maintenance.

A month or so ago, I removed the anti-seize from the entire collet and replaced it with some marine grease that I had on hand. It worked flawlessly for the past month. I thought for sure I had solved the mystery. Infact, I was able to operate the drawbar with less pneumatic pressure than I had in the past using anti-seize.

Not so fast. I was running it today and all of a sudden, it froze up. I activated the drawbar; the ram was activated but the tool did not drop out. I lightly tapped the top of the pneumatic ram with a dead blow hammer and the tool popped out. I cycled it about a dozen times, and it worked flawlessly again. Twenty minutes later…Stuck!!! Heading out to the shop to take it apart again and look for clues. I am truly stumped on this one.


OK. I may have finally found the culprit. I observed the drawbar working fine, then suddenly freezing up. Then working fine again. This made me think that it was not a lubrication issue at all. Looking closely at the setup, I realized that the shaft that extends out of the pneumatic ram and pushes down directly on the drawbar was not perfectly aligned with the drawbar.

With the drawbar fully frozen in place, I manually aligned the ram shaft, so it was perfectly concentric with the drawbar. I activated the drawbar once again and the tool popped out immediately.

I believe the problem was that if the shaft is not concentric with the top of the drawbar, the actual drawbar probably bows slightly along its length causing the tapered portion of the collet to jam in the spindle. Just my theory. Time will tell.

Best… Richard