I have recently acquired a Sherline lathe, and I am learning how to use it. I have run into a problem that I sure those of you with more experience (or practically any experience) can help me solve. I needed to center a 3/8"-16 threaded hole in a Delrin cylinder.
The first couple of times that I did this, it worked great. I put the workpiece in a 3 jaw chuck, faced each end, and then used a center drill in the tailstock to make a small hole. Then I used a 5/16" twist drill in the tailstock to enlarge the hole, and then used a 3/8"-16 tap. The first two times that worked well, I was doing this to a cylinder that was only about 3/4" long.
Then I tried to center a hole in a 3" long cylinder, using the exact same mechanism--and it didn't work. The hole was way off--about .05" difference from one side to the other.
Possible sources of difficulty:
- I know that twist drills are intrinsically less accurate than center drills. Should I look for a 5/16" center drill to make the pilot hole for the twist drill? Or should I start with a twist drill the diameter (or slightly smaller) than the pilot hole of the center drill, and gradually move up in size?
- Is it possible that that the 3 jaw chuck can't hold a piece of Delrin that long without high speed rotation causing it to wiggle slightly off-center? Is the solution to drill the center drill and/or twist drill at very low speed?
Clayton E. Cramer snipped-for-privacy@claytoncramer.com