I have a 30" x 48" cnc router built from a kit. It has aluminum extrusions framework and aluminum panels for gantry and two ball screws on the Y axis, second one slaved to first one in Mach3. Problem is when calibrating the Y axis in Mach3, when I get it as close as possible, then when return to where zero was and reset it to xereo, I run it out a given distance and it might be right on but then return to zero and its not on zero by about an 1/8". Or I might have it set on zero and run it out a given distance and it might be off about 1/16" to 1/8". I checked the couplings on the stepper motors and there doesn't seem to be any play there. Seems like I'm chasing my tail and getting nowhere. Any suggestions? Thanks in advance.