Denford Software & Machines

Can anybody give me a guide as to the maximum spindle speed I should be able to single point thread a M8 x 1.0 thread in mild steel on my Mirac without loosing pitch.

I get the feeling at 250 revs using 20 passes there is little/no torque in the spindle and its stalling for a split second and loosing pitch. Has the Mirac got electronic gearing for threading?

Or is it something more sinister that's at work.

Thanks
Graham

From what I remember, the max feedrate for threading (on the old LCB3 control boards) was around 320mm / min.

So a 1mm pitch is around 320 rpms. The coarser the pitch, the slower the max rpms, but there was no real hard and fast rule.

There is electronic gearing between the spindle and axes but as these machines use stepper motors the axes may stall & loose position. Lighter cuts during threading passes?

Thanks for the reply, I have 3 meters of 10mm diameter bar so I can experiment for a while yet

Graham