Z-axis accuracy problem

[ljr8378]

I have a CNC Taig mill. I want to surface an aluminum part to a 0.005" depth. I use a probe to locate the surface of the part and I have an accurate tool offset, but when I run the g-code I get a z-axis variation of up to +/- 0.010" (which will not work well for a 0.005" depth surface operation.) Note that I have calibrated all three axes and they seem to be accurate.

I converted the values in the UCCNC software from metric to English units (not sure if that was a good decision.) I have attached copies of the "General" and "Z-axis" screens. Are the linear error values too high (I used the default values and divided them by 25.4 to obtain the English values)? Can anyone tell me what I am missing? I have to believe that I can get greater accuracy then +/- 0.010"

Thanks,

Lauren Rezac