I am working on somewhat small part. 14mm to be exact. Sometimes running the same program several times causes a height variation of 0.5mm. Part is designed to have a lip of 1.7mm and the final is 1.1 to 1.2mm.
I’ve figured out on holes I need to go 0.15 under in my model to get the dimension I want. And vise versa for a cylinder; 0.15mm over on my design. I think this has to do with the fact with a .125 cutter the lowest meshcam will allow me to set the tolerance to is .002544.
I have another part I make regularly. I cut 3.5mm panels. Some of the times it comes in at 3mm.
There is no deflection in the part. The mill is .60" from end of collet. Machine is kept clean.
I need to figure this out as my burl blocks are $150/ea.
Have you done a hole pattern and diamond-circle-square test cut to determine runout / calibrate your machine?
My suggestion would be (once you’ve got things dialed in) to leave a roughing clearance larger than your current error, then switch to a suitable brand new bit which you know to be sharp for a finishing pass. Alternately, for a hole, make a jig which will also serve as a fixture to hold the piece and make the final size of the holes w/ a suitable drill bit on a drill press. Sometimes handwork is better than machine.
Remember though, wood is a natural material, and unless you’ve stabilized the burl w/ epoxy, it will move after being cut and pieces are exposed to air / moisture and as ambient RH changes.