I have a Harbor Freight Mini-Mill that I converted to a 3-axis CNC machine using a Heavy Metal ball screw conversion kit with Automated Technologies electronics. I use Fusion 360 for design and have installed the Mach4 post to my local library from Autodesk's website. I have made a small bottle opener to test. Every time I run the g-code the bottle opener comes out about half size. The scale between my design and the actual part when cut always seems to always be off and it comes out shrunk. My machine setup units are set to inches and my unit mode is set to metric. Could it be my motor settings are off?

Motor Settings:
  counts/unit; 40960.0
  units/minute; 35
  units/sec^2; 0.49

My motor has 200 steps (1.8deg.) each and has a 128 microsteps.

My math: (200*128)/(0.625)=40960.0 counts/unit

Motor Settings:
  counts/unit; 40960.0
  units/minute; 35
  units/sec^2; 0.49

My motor has 200 steps (1.8deg.) each and has a 128 microsteps.

My math: (200*128)/(0.625)=40960.0 counts/unit

For one rev of the motor your axis should move .625", Put a mark on the end of the motor shaft and on to the case and enter the following code in MDI:-

G20 G01 G91 X0.625 F2.

If the machine moves .625" and the lines on the motor are in line its not the machine.