5C collet closer drawbar threading problem

We are building an air operated 5C collet closer.

The drawbar we are making is machined from a piece of seamless
mechanical tubing. We've got it adjusted for zero runout.

We are cutting a 1.044" OD x 24 TPI thread on the outside of a 1.250"
piece of tubing turned down to 1.030" This will pull on the internal
thread of the collet to close it in the chuck.

We've threaded two of these drawbars now and both times the collet has
significant runout when threaded to the drawbar. Why ? The thread
seems to be high quality. The collet seems to be OK. The drawbar runs
true. Why does the collet have runout when screwed on ?

What is the solution to this problem ?

I'm tempted to cut the thread loose so that the collet can center itself
in the chuck irrespective of the drawbar position.

Any help would be appreciated. Thanks.



Kim Lux <lux@...>