Toolholding in Collets: How to Avoid Tool Pullout

Feb 5, 2011 // by Bob Warfield // Blog, Techniques // No Comments

Tormach has published a great report on variables that influence the holding power of R8 collets. You can view the pdf file here.

They basically did a series of tests while changing various things to see how that affected the amount of force needed to pull a tool out of an R8 collet. One of the most damaging things to the holding power is the protective oil that cutters come coated in. Cleaning that oil off and torquing the drawbar to 40 ft lbs resulted in an increase in holding power from 1300 lb to 3600lbs–big improvement!

The difference on a clean and dry shank based on drawbar torque from 20 ft lb to 40 ft lb was an increase from 1850 lb to 3600 lb. It’s worth it to drag out your torque wrench and “calibrate” your arm for what 40 ft lbs feels like.

They performed a number of other tests, but at the very least, keeping that tool shank clean and dry coupled with proper torque should be your starting point.

I’ve also seen figures on the proper torque for ER collets, and these are often much higher than machinists assume. See my article, “Getting the Best Performance from ER Collet Chucks” for some more info.

Note: The link for ER Collet Chucks goes to the new CNCCookbook WordPress site. It’s coming along nicely, but there is no content there that isn’t available here. If you would like to use an RSS Reader, like Google Reader, so you don’t have to check back here constantly for new posts, that’s the way to do it. I’ll get an email feed going there soon too!