Need Help!- What size stepper motors for Bridgeport mill?

[CATCH22]

Im wondering if 750oz in stepper motors would be powerful enough to run my Vertical Bridgeport series1 mill. I was also planning on going with a 2 to 1 ratio on the timing pulleys so that should help too. So I think this should be ok, but Im not sure. Any input would be great.

Thanks Mike

[Oldmanandhistoy]

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What size servo/stepper motors for Bridgeport?

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What size servo/stepper motors for Bridgeport?



John

[HimyKabibble]

Originally Posted by CATCH22 Im wondering if 750oz in stepper motors would be powerful enough to run my Vertical Bridgeport series1 mill. I was also planning on going with a 2 to 1 ratio on the timing pulleys so that should help too. So I think this should be ok, but Im not sure. Any input would be great. Thanks Mike

I would expect 750s to work, but they won't be speed demons. With 2:1 reduction, I expect you'd be lucky to get 100 IPM rapids.

One key difference between steppers and servos is their torque-speed response. Steppers have max torque at low speed, and speed falls off rapidly at higher RPMs. Useful RPM is often limited to under 1000 RPM, especially for larger motors (NEMA34 or 42). So, to get the torque you need, you either go with a high reduction, or a larger motor, both of which reduce your top-end speed. Servos usually will operate at MUCH higher RPM (mine are rated for 4200 RPM), which allows you to use a greater reduction ratio, and still achieve very high rapid rates.

You should consider going with servos. They don't cost a great deal more, compared to the overall cost of a decent conversion, and will give you greatly improved performance. I have 850 oz-in (peak) servos from www.homeshopcnc.com on mine using Gecko G320s, and I can get 400 IPM rapids with 2.5:1 reduction. Were I to do it over again, I would go with a higher reduction (4.8:1), to bring the max speed down - 400 IPM is WAY too much for a machine this size. 200 IPM is more reasonable. Even with the 2.5:1 reduction, I have more than enough torque to instantly snap off a 1/2" endmill, and it doesn't even lose position doing it.

Regards,
Ray L.

[bwpigeon]

I have heard that you can use the servo motors from a tread mill. If so how do you determine just how big they are?

[HimyKabibble]

Originally Posted by bwpigeon I have heard that you can use the servo motors from a tread mill. If so how do you determine just how big they are?

I know several people who've used treadmill motors as servo motors, on knee mills and large CNC routers, and are VERY happy with them. At $20 each (www.surpluscenter.com), tough to beat! The encoders will cost 2.5X that.

Regards,
Ray L.

[CATCH22]

I wonder how the tread mill motors stand up compared to an actual servo motor,and how would you hook up an encoder they look like they only have the shaft on one end?

[HimyKabibble]

Originally Posted by CATCH22 I wonder how the tread mill motors stand up compared to an actual servo motor,and how would you hook up an encoder they look like they only have the shaft on one end?

They work surprisingly well, even compared to real skewed rotor servos. Many of then DO have a 1/4" or 1/8" shaft at the back end, which is perfect for mounting an encoder.

Regards,
Ray L.

[CATCH22]

Would you be able to run these motors with Mach3 software,they would have to be set up to take step and direction signals? Possibly with a gecko drives?

[HimyKabibble]

Originally Posted by CATCH22 Would you be able to run these motors with Mach3 software,they would have to be set up to take step and direction signals? Possibly with a gecko drives?

Yes, with G320s or G340s.

Regards,
Ray L.

[CATCH22]

Thanks for your help guys!!!