So George, what you're suggesting is a knee-mill style of bed lift for a CNC router?:whistling:

Incidentally the Nm rating of a stepper motor has very little relevance to its operating capabilities. The figure oft quote is the holding torque, when it is stationary. Except for some specific applications this is rarely the case, as torque drops of with speed.

In answer to your question F = 2*pi*T*e/p where p is pitch in m, T is torque in Nm and e is efficiency, or T = Fp/(2*pi*e). For a ballscrew e=.8, for trapezoidal e = .3

So for a 5mm pitch trapezoidal screw, lifting a 10kg weight (100N force) a torque of 100 * .005/(6.28*.3) = 0.27Nm is needed at the actual working speed.

Then you have to consider if the motor can hold the weight up when it is stationary. For trapezoidal the efficiency is low so there is relatively little push back.. But with a ballscrew with a long lead (pitch), typically 5mm or bigger, that weight will push back on the motor, so as soon as the power is removed or reduced the weight will fall... this may or may not be acceptable... There are formulae to work this out, but I'll leave that as an exercise for the reader...


Oh, you have of course checked the Euler buckling loading for your chosen screw?