Having been away from the workshop on a family break, I've been itching to run off another example, with a few changes / enhancements made for good measure:
- Increase the threading speed. Currently 500rpm but it seemed happy when running over 1000rpm - I had no programmed dwell between the 2000rpm turning spindle speed and the lower 500rpm speed used in the subsequent threading operation, yet it seemed to cope fine during the initial phase where the spindle was still decelerating.
- Slight increase in diameter of the taper. This is a very shallow taper and although the finished dimension seems close to tolerance, there is little visible clearance between the axial faces of the taper and collet when assembled. So a more finite / visible gap would be reassuring.
- Use a VNGT (polished and honed) insert for the roughing and turning operation, to see if I can get a better surface finish. These are often described as being "aluminium cutting" inserts but some are actually specified as also being suitable for medium to light machining of steel. True, they have no coating but buildup and chip welding doesn't seem to be an issue for light cuts.