Superior Electric Steppers

[JAZZCNC]

I'm wondering again whether those Leadshine 3ph Nema23 2Nm closed loop steppers wouldn't do the job or is the torque characteristic for a servo very much different to a stepper?

Very different.!!

The 1.3Nm is continous meaning thats what you'll get at full motor speed probably 3000rpm. The 3.6Nm is Peak torque which the drive/Motor can handle for limited period of seconds which is often enough to handle high enertia or heavy starting loads. Under heavy loads ie: cutting it will handle anywhere between 1.3nm & 3.6nm for limited periods depending on loads.
Throw into the Mix that because Rpm is often much more than required there will ratio applied so torque actually increases.

Stepper rating on the other hand measured at ZERO RPM and starts to drop as the Rpm's increase. Slowly at first up until point of the Speed curve where it starts to drop quickly untill full motors coils reach full saturation and motor stalls. On 34 motor the speed curve will be aprox 900rpm depending on inductance and voltage used. There'll be little to no torque at 1500rpm.

This is why inductance and Voltage is so important to the speed you get from steppers. Also you throw how stepper is wired into the mix and it can change again.?
If wired parallel you'll get torque higher up the rpm range but less lower down for set voltage. If wired series you'll get pretty much the opposite, Higher torque lower down rpm range but motor will reach saturation much sooner for the same voltage so lower RPM.

Most 34 motors are 4 wire series wound motors and to get any decent speed from them requires High Voltage. Often larger Nm 34's are run with mains voltage drives.
Now for mill you won't require high rpm's so series wound is often Ok. Nema 23 motors often come with 8 wires and can be wired series or parallel. But the same applies in that higher voltage is required for same rpm if series wound.

So in nut shell if they Fit 1.3nm Servos then 2Nm Nema 23 Stepper isn't going to cut it really.