I would like more too, but the motors and drives I have were free.
Just didn't want to go through the work of doing all this to find out
the motors are not strong enough. The drives can handle more than the
steppers need, so that is one option.

I think I will go for a 2:1 reduction. I am well aware there are
going to be a lot of limitations to the system, but when I get it
working I can then determine the value(to me) of upgrading to
eliminate those problems.(the ultimate would be a full servo system w/
enough power to direct drive, but that get's expensive).

Has anyone every done a blended system,some stepper and some servo?

JW

"zephyr" wrote in message ...
I did a retrofit on a Chinese mill/drill. I used 425 in-oz motors with 0.1"
pitch lead screws on the X and Y. I would have preferred even more torque
but the motors were free. The machine worked OK for most small jobs and I
didn't have problems with loosing step except at fast speeds. Step motor
torque goes down fast as the speed is increased. On a Bridgeport I think
the lead screw pitch is larger like 0.2" or 0.25" so I would definitely
recommend a 2:1 reduction on 300 in-oz motors. Most retrofits and even
Bridgeport CNCs have the z axis motor on the quill not the knee. I think
that makes more sense considering things like drilling cycles.

John


Jeridiah wrote in message ...
I am considering doing a CNC conversion on an older Bridgeport. I am
wondering what the torque reqm't would be for stepper drives. I have
some 300 oz steppers, but I don't think they would be big enough.
Maybe ok for the X/Y, but definetly not for the Z(if I move the knee).

Anyone out there have a good number to stick to these? For now, I
plan to use the stock ACME screws, but would like to upgrade to
ballscrews at some point. I know that the ACME screws are going to
have a higher torque reqm't.

JW