Is it possible to slave the Z axis to the Y axis?   I have a 3 axis controller that I want to use to test a plasma cutter.   Is it possible to reassign the pins or slave the Z axis to the Y axis to test the movement as I have 2 steppers on the Y axis and not enough axis on the Stepperworld board to control them.

Thanks

Dont really follow what you are asking, if you are attempting to drive two motors from one drive then I cant say how successful that would be but Mach has nothing to do with it so no problems from the Mach end of things.
Hood

Since I don't have an A axis to slave for the 2 motors needed in the Y axis.   Is it possible to slave the Z axis (which i'm not using) to the Y axis to run the addition motor needed on the Y axis.   I'm not talking about driving 2 motors from the same axis.   Just slaving the Z axis to the Y.

You just call the extra motor/axis the A and slave it to the Y.
Hood

If the both axis use the same drive setup you could tie them to the same outputs - if everything will cooperate electrically. The advantage of slaving it using A is that you can then do some things with limits and homing that you can't do the hardwired way.