We have been running a used geometric die head in the tailstock of our lathe for a while now, several thousand parts at least. We're cutting 3/8 -24 threads on 12L14 material at 220 rpm. We're only cutting 1-3/8" of thread length that does not thread to a shoulder. The threads were turning out perfect, until we had a part that had what i believe are called tapered, shaved, or stretched(I read another post with the same issue that called them by this name) threads. Upon inspection, we found we had a chipped chaser. So we ordered 2 more sets of identical chasers and sent in the damaged set for repair. When we got all the chasers back and setup to run more parts, we began getting these "shaved" threads. After trying all 3 sets of chasers and sweeping the circumference of the die head with a test indicator mounted in the Chuck to check for proper alignment, we refered to the geometric die head manual and concluded that our used die head might be worn.
We then purchased a brand new Rubometric die head, which gave us the same results. The style of both heads is style 3/4 D. So neither of them are adjustable for alignment. We spoke to our chaser supplier to confirm that our 45 degree chamfers on the work are compatible with the 22 degree chamfers on the chasers as well.
So my question is, what else could be the problem? The thousands of parts we successfully ran on the original set of chasers, we didn't help feed the tailstock. During our troubleshooting we did however, with no noticeable results.
We then purchased a brand new Rubometric die head, which gave us the same results. The style of both heads is style 3/4 D. So neither of them are adjustable for alignment. We spoke to our chaser supplier to confirm that our 45 degree chamfers on the work are compatible with the 22 degree chamfers on the chasers as well.
So my question is, what else could be the problem? The thousands of parts we successfully ran on the original set of chasers, we didn't help feed the tailstock. During our troubleshooting we did however, with no noticeable results.