Keister

Welcome!

Ok. I'm assuming you know little about stepper motor characteristics so forgive me if this is a bit basic. A stepper motor has two 'modes' of operation. Below the 'corner speed' - which is governed by a complex equation using the motor inductance and the motor supply voltage - the motor torque is essentially flat. Above the corner speed the torque drops linearly as the revs increases.

With your driver you need a 7.5ohm resistor at 24v (to keep the motor current at 2.8A - 8ohm is fine) and 12ohm at 36v (do not run the 36v supply with an 8ohm resistor, you will overheat the motor and could demagnetise it), but changing the supply voltage (and therefore the resistor) will make no difference to the speed of the motor. The problem here is you are running a non-current-limiting unipolar driver - therefore the supply voltage has no effect, the only voltage the motor sees is that driven by the potential divider effect of the motor resistance and the external resistor - effectively your motor is running at 2.8v and has a corner speed of about 110rpm. I am surprised you are only getting 30mm/min (is that really correct - how did you measure this if you have not got them attached to the mechanics? and what screw pitch are you using?).

The power supplies you have are fine - its the driver that the problem. A unipolar driver is incredibly inefficient - its fine for tiny stepper motors but completely useless for big ones like this except at very low speeds - pointing an astronomical telescope for instance where the short term power dissipation during the few steps a second allows for a simple driver.

Change the driver for a decent bipolar one and run those steppers in bipolar parallel mode and it'll be fine at 24v, the corner speed would be around 1000rpm. You don't say what screws you are using but a 3mm pitch trapezoidal screw will achieve 900mm/min (a reasonable cutting speed on a small 300mm unit) at 300rpm and thats easily within the capabilities of these motors. Even a 1mm pitch threaded rod should give you 500mm/min without too much trouble on a decent driver.

I hope you didn't pay $95 for that driver as shown on the CJ website, thats a real con for its incapabilities compared to whats available elsewhere...