Steppers for Converting Sieg X2 to CNC?

[irving2008]

If you ignore the centre taps then you'll be wiring them full-coil bipolar - this will double the resistance giving a rated current of just 1.05A.

Actually the current wired bipolar series is 0.7 * rated = 1.47A, so those drivers would need to be run at 1.2A, but the holding torque is 1.4 * rated.

So assuming they are 1Nm (141ozin) motors:
Bipolar 1/2 coil: Rated 2.1A, run at 1.8A, torque = 1.8/2.1Nm = 0.85Nm (120ozin)
Bipolar Series: Rated 1.47A, run at 1.2A, torque = 1.2/1.47 *1.4 = 1.14Nm (160ozin)

So run them Bipolar Series since you'll get low feed rates anyway due to leadscrew inertia and frictional load...