WELL, I tried working up one using Mach3 but it made a lousy CMM. with a true cmm you freehand the movements and get measurements. With Mach3you have to drive the machine movements and it takes MANY different Probing routines and you have to work out the backlash to boot.
Now if you are talking just using the encoder function to build a simple xyZ freehand motion machine it works fair, BUT not having kenimatics to work out the joint motions you are limited to straight Linear moves with NO rotary joints.
Been there done that one, (;-) TP