>I built a desktop milling machine a couple of years ago.  It used
>5v rated steppers, so I hooked them up to 5volts.  I got no torque
>out of them at all.

That would be correct.

>Called the guy I bought them from, and he said that, though rated
>for 5volts, steppers need at least 4 to 6 times the rated voltage
>to work properly.

The 5V rating is what you would use to supply enough current for them to
hold position. This limits the coil current to a value that limits heat
dissipation.

>I run my mill on 24volts.  Has plenty of torque, and have never
>had a problem with any of the motors.

That would be a typical voltage to get the current to increase at sufficient
rate while stepping. However if leaving a motor stopped for a while at this
voltage you will find the motor will get very hot, possibly damaging winding
insulation. The way I have seen this sorted is to use a switchmode regulator
chip with a "change voltage" control done by an external transistor changing
the sense divider ratio. When the control processor wants to move the motor
it switches to high voltage, waits a few milliseconds then starts stepping
the motor. A few milliseconds after finishing the motion the voltage is
switched back to the holding voltage.

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