I built a JGRO but I'm having a problem with the size of the parts that I'm cutting. I've thought about this for a long time and I have no idea what is wrong.

Some background info:
Aspire to create tool paths, outputting using Mach3 post processor
Mach3 to run the g-code
1/2-10 acme screws, all axes
I have probotix bi-polar drivers
PacSci bi-polar motors
The steps per inch are all the same, (1600 or 16000, I can't remember, running 1/8 microstep either way)

If you need any more info let me know!

I created an extremely simple program to cut an ID and an OD. Both were drawn to 2 inches in diameter. I'm using a 1/4" router bit. For this program I roughed the diameters leaving 0.050 (on the radius) and then went back and did a finish pass. In Aspire I used the profile command for both circles.

The ID is coming out undersize and the OD is oversize. If there was an incorrect setting or something I would expect them both to be small or both to be large, not one large and one small.

Both the ID and OD should be 2.000 inches. The ID comes in at 1.960 and the OD measures 2.045. Both of these features were cut during the same program and with the same tool!

Here's the kicker, the slots left from the router bit are exactly what they should be: 0.300 inch (remember I used a 0.250 bit and left 0.050 during the rough cut.

I want these features to come out the same size! I need some help badly!