Hi,

I'm in the process of fitting my MJ189 mini lathe with stepper motors (x/y). I have already replaced the spindle motor, it's now a DC servo motor with gecko drive. Using a PC to control via parellel port, I can get 1500RPM that seems controllable as I'm using a step multiplier.

I want to screw cut but the lead screw is not directly connected to the spindle drive, it's manual now but will have a stepper motor on it. The spindle can index with step/direction. Has anyone managed to screw cut with a simlar setup? I understand, normally you'd have gears comming off the spindle controlling the feed rate of the lead screw. In this case I propose using the synchronised step/direction of the spindle motor and stepper motors combined to produce the same effect?

Dan

With the spindle driven by a gecko, you have the option of just making a coordinated feedrate move.

From Z0
G01 Z-10 C 3600
should given you ten threads at 1mm pitch.

I use TurboCNC on my CNC'd Minilathe, and you just need to provide a 1/rev encoder pulse, and TurboCNC sync's the Z axis to the spindle rpm (electronic gearing). It works great, and TurboCNC has a canned cycle for multi pass threading G76.

http://www.wrathall.com/Interests/CNC_conversion/spindle_encoder.htm