sploo
Somewhat extinguished member
I've seen a few references to finishing the last few turns by hand when cutting a thread (where it's not possible to have a relief cut, so risking a crash with the lathe powered). I have basically zero experience of thread cutting on a metal lathe though.
That got me thinking - is there a minimum rpm speed required for thread cutting steel, using HSS cutters?
The reason I ask is that I'm looking at building a 4th axis for my CNC milling machine, and its main use will be for turning very large objects (e.g. 40cm diameter) - so I'm planning on gearing it to run very slowly (e.g. maybe 5 to 10 rpm; but obviously with significant torque). With appropriate cutting depths, and a sufficiently rigid tool mount, would there be any issue with getting it to turn threads on ~3mm to 20mm diameter stock at this sort of rpm?
I guess this comes down to whether HSS cutters have a surface feet per minute sweet spot; and this low rpm combined with a small diameter would be just too slow.
That got me thinking - is there a minimum rpm speed required for thread cutting steel, using HSS cutters?
The reason I ask is that I'm looking at building a 4th axis for my CNC milling machine, and its main use will be for turning very large objects (e.g. 40cm diameter) - so I'm planning on gearing it to run very slowly (e.g. maybe 5 to 10 rpm; but obviously with significant torque). With appropriate cutting depths, and a sufficiently rigid tool mount, would there be any issue with getting it to turn threads on ~3mm to 20mm diameter stock at this sort of rpm?
I guess this comes down to whether HSS cutters have a surface feet per minute sweet spot; and this low rpm combined with a small diameter would be just too slow.