Hello

It would be really nice if I could get your opinion for a stepper motor buying decision. It is for a 4 motor 3 axis CNC machine for wood machining, featuring a 2.2kW air cooled spindle.

The setup is:
– 2005 ball screws with 12mm machined end for joint coupling
– 8mm/12mm round or 14mm/12mm keyed plum flower type shaft coupler (depending on choice below)
– 20mm linear rails

The drives are 4 x DM556T (made by Leadshine), featuring the following current table choices:
Peak RMS
– 3.8A 2.7A
– 4.3A 3.1A
– 4.9A 3.5A
– 5.6A 4.0A

The choice is between:

1) NEMA23
Current / phase 4.2A
Resistance 0.9 ohm
Rated Voltage 3.78V
Inductance 3.8mH
Holding Torque 3Nm
Phase / Wires 2 / 4
Shaft 8mm

2) NEMA34
Current / phase 4.0A
Resistance 0.31 ohm
Rated Voltage 1.36V
Inductance 2.86mH
Holding Torque 4.5Nm
Phase / Wires 2 / 4
Shaft 14mm

Price is not an issue here, as both solutions are virtually identical in price.

I saw a number of posts online that recommend NEMA 23 over NEMA 34 based on smaller motors having a larger torque at higher RPMs – as required by the 5mm ball screw. However what attracted my attention to this NEMA 34 motor was the very low inductance (even compared to the NEMA 23) while also providing a higher holding torque. Unfortunately I don't have any torque diagrams available.

Further, the NEMA 23 has a 8mm shaft, whereas the NEMA 34 has a 14mm one. The 20mm ball screw is 12mm diameter with respect to the coupling connection. Would you be concerned going from 8mm to 14mm with the coupler?

Could you please let me know your opinions?

Thanks,
Christian