Posted by BillS on May 29, 2012 at 23:29:13:
In Reply to: Re: Tooth jump on internal gear from Fellows 7A shaper posted by Greg Scott on May 29, 2012 at 22:56:43:
Greg, it seems that the slide is moving before electrical cutoff occurs. The slide is moved by the feed cam and roller-follower. I would suggest putting a dial on the slide and manually rolling slowly through the cam's cycle to see if the slide makes any small movement just before falling away. This should help to isolate the problem. I'm not sure what the proper name is, but I'm using "Slide" to refer to the head supporting the cutter ram that rides on machine ways.
We used to have a problem with a 4150 HT material, where one or two teeth overlapped at the end of the finish cut (end of cycle). This resulted in a slight additional metal removal on the last teeth cut. We were cutting external, but this resulted in having to cut twice to minimize the "low tooth" we were getting.
I'm saying this just to point out that there might be spring in the setup, wear in the cutter ram - something that responds to change in cutting pressure during the overlap. Although, I would expect a reduction in cutting pressure would cause a deeper tooth on your internal gear. Since you observe a higher tooth, my money is on the feed depth cam and follower allowing the slide to back away just before cutoff.
One other possibility is backlash in the worm/worm gear drive for the table. Your higher tooth may actually
be a fatter tooth resulting from backlash take-up in rotation - just guessing here.