[bigpete_h]

Hello,

I am looking at converting a knee type bridgeport mill to cnc.
I local company in Melbourne sell 3 axis cnc stepper motor kits which can run under mach 3 control but cannot tell me what size motor I need to drive a bridgeport type mill.
The largest they sell is a 1200 oz/in motor.
Is this motor size (power) sufficient, if not what do you recommend.

Regards Peter.

[SCzEngrgGroup]

Hello,

I am looking at converting a knee type bridgeport mill to cnc.
I local company in Melbourne sell 3 axis cnc stepper motor kits which can run under mach 3 control but cannot tell me what size motor I need to drive a bridgeport type mill.
The largest they sell is a 1200 oz/in motor.
Is this motor size (power) sufficient, if not what do you recommend.

Regards Peter.

I can tell you what I just did on mine, though I used servos, not steppers. I used 850 oz-in peak/170 oz-in continuous motors on X&Y, with 4-pitch ballscrews and 2.5:1 belt reducers. On Z, I used the same motor, with the stock 5-pitch leadscrew, 2:1 bevel gears, and 4.8:1 belt reducer. This gives me over 300 IPM on X & Y, and about 70 IPM on Z.

I believe stepper-drive BPs typically use 650-850 oz-in motors with 4-pitch ballscrews and 4:1 reducers. You'd want a larger motor on the knee, if you drive the knee. Probably could get by with the saem 650-850 oz-in motor, or perhaps a smaller, on the quill, if you go that way. I believe the quill is typically done with a 5-pitch 5/8" ballscrew, while X/Y are usually done with 1" or 1-1/4" ballscrews, which will both typically be 4-pitch.

Best way to start, however, is to measure the torque required to move your axes, and decide what performance level you need, then calculate how much power that requires, and work backwards to calculate the motor performance required to get there. Leave plenty of margin, as the load will likely increase over time.

Regards,
Ray L.