[rmachinist]

Hi,
I'm going to replace my damaged Nema 34 with a new one, I would like to ask what would be better for my Z axis PM-25MV Mill Nema 34 with 12.0 Nm(1699.68oz.in) or 8.25 Nm(1168.53 oz.in) it's like all most the same price for the bigger motor, I'm not sure if there is any pros or cons for ether one


https://www.amazon.com/gp/product/B0...PTXF2T90&psc=1

or

https://www.amazon.com/gp/product/B0...GWISS7BL&psc=1

Thanks

[pippin88]

What is the inductance of each motor?

What voltage will you be driving it with?

With steppers, bigger (higher oz.in) is often not better. You need the torque to be available at reasonable rpm.

[rmachinist]

I have a 60 volt dc power supply I wanted to use, the Motor Specification are listed in the links I added: https://www.amazon.com/gp/product/B0...PTXF2T90&psc=1 or https://www.amazon.com/gp/product/B0...GWISS7BL&psc=1

[arizonavideo]

For the PM-25 a 640 oz 6A Nema 34 is already over kill.

A 1600 is crazy.

Total over kill size would be a 900 oz. The Z runs fine with a Nema 23 570 oz.

[rmachinist]

I'm thinking bigger is better this is why I’m asking, please correct me if I’m wrong it would be easier and work less with a bigger motor I know 8.25 Nm(1168.53 oz.in) can handle it but for all most the same price I can get the (1699.68oz.in) I'm not sure if there is any pros or cons for ether one
Thanks

[ger21]

Smaller motors run faster and smoother. Once you get to a certain point, anything larger actually will decrease performance.

[dazp1976]

I had problems with a 1600oz on mine using 60v psu. Forget it!. Terrible power and resonance issues.

I now have a 1080oz 8 wire nema34 wired in parallel. inductance of 3.5 and runs smooth and quiet up to 2000mm/min which is enough for me. My Z is set up pretty tight.
https://www.ebay.co.uk/itm/1-PC-Nema...72.m2749.l2649

The drivers I'm using are cheap ones so I'd probably get more from it with better ones.

[rmachinist]

Smaller motors run faster and smoother. Once you get to a certain point, anything larger actually will decrease performance.

larger they have more power and torque?

[pippin88]

I suggest you search and do some reading on stepper motor selection.

These questions have been answered many many times here on cnczone and elsewhere.

Have a look at stepper motor torque curves.

Don't buy anything until you understand whether it is a good choice.

[sn4k3]

Beware, I was in same path as you but got some light, please see this post: https://www.cnczone.com/forums/stepp...99300-cnc.html

[kawazuki]

larger they have more power and torque?

Unless you are trying to shift huge bulk, quickly and have the power available to service that performance, a smaller / lighter motor will perform just as well. The 2nd of the two above noted motors has the lower inductance and so would match your power supply better although it still would be slow compared to a 'lower rated' oz/in motor that is better suited to the power available.

[ger21]

larger they have more power and torque?

They have more holding torque, when they are NOT spinning. Once you get over a few hundred rpm, they often have less torque than much smaller motors.