Greetings:

I was using a Gerber CNC mill, the spindle is a Makita router, the CNC is handled by Mach3 and the GCode obtained from Vectric Cut 3d, with a 1mm stepp per sweep, the machine had its Zaxis stepper changed recently.
As it was rough pathing a block of MDF and little over half of the work done, the z axis failed to raise properly, and seemed to actually dive deeper than programmed (about 3 mm instead of 1) each time it had to descend.
I am new to this job but the people here say the machine has done this before.
I would appreciate any guidance towards finding out how to fix this.
Thank you