Hi,
steppers lose torque the faster they go. You can try to counteract that by using high voltages to drive them but it seems that 80V is about the limit
for readily available drivers.
The graph attached shows a fairly typical two phase 23 size stepper rated at 198 oz.in. You can see by 500 rpm the pullout torque is reduced to about
half and by 1000 rpm down to about a quarter of rated torque.
On the Tormach website there is a clip where they assign the max speed to any stepper of 375 rpm to ensure that the torque remains high enuf for reliable
motion, ie without losing steps. Tormach are quite conservative. I regularly think that 500 rpm is a reasonable compromise.
If your machine has a 5mm pitch screw then at 500 rpm that works out to 2500 mm/min or about 100 in/min. With a 10mm pitch screw that would be
about 200 in/min but remember a 10mm pitch screw is going to need twice the torque to drive it...you may be in danger of exceeding the pullout torque
of the stepper and create a stall.
Stepper motors are great at slow speeds, in terms of 'torque density' they are better than a servo of the same size. As the speed gets up that's where servos are
come into there own. Downside is that servos, even cheap ones are much more than a stepper. Don't lose hope though...many CNCers use steppers with great
results.....just be aware that there is a speed limitation.
Craig