The length of the flats are .160" on the outside of the large diameter (0.75") and 0.120" on the outside of the smaller diameter. They're also not flat, now that I take a close look. They're definitely arcs in and of themselves.

Outside of the backlash, the axes are very consistent - example: I make a g0 move from x0 to x-3.7500, then from x-3.7500 to x-3.5000. I now zero the glass DRO, and I can make any move in the positive direction and be pretty much dead on (within a couple of ten thousandths, anyway).

Outside of the backlash, the axes are very consistent - example: I make a g0 move from x0 to x-3.7500, then from x-3.7500 to x-3.5000. I now zero the glass DRO, and I can make any move in the positive direction and be pretty much dead on (within a couple of ten thousandths, anyway).

Can you extend this test. Zero Mach3 and glass scales (after taking out any backlash) and then do short moves of 0.01" up to a total of about 0.15" and compare the numbers in Mach3 and the glass scale at each point and see if they correlate. Repeat on both axes.

Dan