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Bridgeport Conversion Torque Reqm't

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

Reply to
Jeridiah
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I have one of the ones Bridgeport used, which is a big Slo-Syn item with something like 300 to 600 oz-in stall torque. This was gear-belted 1:1 onto the ballscrew.

Roughly, mechanical efficiences are 50 percent for acme versus 90 percent for ballscrews. So you'll need to double the capacity of your motors (and power supply) for acme, which will probably cost you more than the ballscrews.

Stepper motors are not a good solution where speed counts. They are hideously poor performers (slow, loss of torque at any decent speed) unless you have a very expensive controller and power supply. Servos are a much better and cheaper solution, especially on the scale of making a big, heavy milling machine table move into resistance.

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Reply to
Richard J Kinch

You could use them with a 2:1 reduction. WHEN(not if) you want more speed, go for it. In the meantime, you stated that you already have the smaller motors. You will learn alot just from the experience of getting them working.

Pete

Reply to
Pete Logghe

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

Reply to
zephyr

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

Reply to
Jeridiah

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