Hi,
I've stuck with calibration of my GRBL-driven CNC router It's was built around OpenBuilds linear rails and has plain simple stepper motors and GT2 belts on x/y axis. I've calculated steps per mm on both axis with caliper and mechanical edge finder on 120mm base(distance between caliper jaws), repetition accuracy on that base was about 0.05mm.
For accuracy check simple part was drawn, it's outer dimensions 70x70mm, circle has 45mm diameter, inner pocket is 30x30mm, plus few holes ranging from 6mm to 12mm. I've checked milled from plexiglass part with same caliper and it has all outside dimensions smaller by 0.1mm(which seems OK for that style of linear rails) BUT all holes and central pocket is undersized by 0.3mm. I've ran G-code for pocket and holes few times with intention to eliminate influence of low stiffness of aluminium profile and overall construction, but in all subsequent runs barely any material was cut. I just couldn't understand why all inside dimensions has three times bigger accuracy error Any ideas?
If it matters G-code was generated in Fusion360 and streamed to Arduino through bCNC.
PS I've also checked numbers in generated G-code, toolpath looks accurate, without any unwelcome compensation.