Is it possible to gang stepper motors together to produce twice the torque?

Question

Maybe on at each end of a threaded shaft, wired in parallel to drive a s***w

Answer 1

They would have to be aligned to within a small fraction of their step angle, otherwise the two motors would be 'fighting' each other constantly over that misalignment.  

Example: the step angle is 2 degrees; the shafts are connected together; the poles of motor 1 represent the 'reference', but motor 2 is off by 1 degree.  While motor 1 is 'happy', motor 2 is in a state of maximum torque, constantly trying to shift 1 degree (depending on the selected direction of rotation).  That will nullify any torque you are getting from motor 1, as it is now fighting to maintain its position.  The 2 motors will eventually settle in on the reference angle + 1/2 degree in a state of low-energy equilibrium, to where any external force will set it off +/- 1/2 degree, and thus the motors will fight for position, again.

If you can align them nearly perfectly, and find 2 motors with precisely matched step angles, then what you propose is possible.

.

Answer 2

Anything is possible...that being said, use the ONE ideal stepper motor for the application...