I have a home built OX CNC running Mach 3. I am using Fusion 360 for CAD and CAM. I am having a problem with my Z depth cutting deeper than the G-Code is set at. I am cutting a 2D pocket that is set at -3.2mm below Model Top. The pocket is a 7' x 3" rectangle with radius'd corners. It is cutting starting at -3.6mm and going down the first Y travel it goes to 3.94 mm. As it runs the first X segment it goes to 4.80mm. As it comes back on Y it goes from 4.8mm to 4.17mm. As it comes back on X to the starting point it goes back to 3.6mm. The G54 machine coordinates show -3.2mm and I checked the code and it is the same. I posted on the Fusion 360 site and a comment suggested it is a problem with Mach 3 or the post processor. So it is staring off at -.40mm below G-code which is acceptable but not great. It goes to -1.60 deeper than it should at the opposite corner and comes back up to -.40mm.
I have tried everything I can think off. It is notable that my X and Y axis cuts are very accurate.
I am cutting 19mm starboard plastic which is very flat. The material is securely fastened to the table.
I put down a new spoil board and fly cut it to ensure it was parallel to the z plane.