After battling for a few hours, I still seem to have a little nod in the Z axis. I put a straight board front to back, lowered the surfacing bit to touch. Then I loosened all the riser bolts . I stepped the Z down 0.005 then tightened all the riser bolts back up. Repeating at the other end of the X axis. It took some nod out, but on a 2.5 inch surfacing bit I still get a thousandth or so ridge at the front. Is there a better method to do this? I really don’t want to shim the spindle?
Hmmm, not sure what your reservations are to the shims. I would strongly recommend the shims. I got a variety pack of brass shims. Yes, there is a definite amount of trial and error as you figure out the exact amount of shim thickness you need. But that is a one off, and they just work after that. Good luck.
There’s two types of nod shimming… You shim between the carriage and the gantry if the Z motion is not perpendicular to the table, and you shim between the carriage and the spindle if the Z rotation is not perpendicular to the table. Beyond that it doesn’t really matter where in your stackup the shims go, but keep them close to the bolts so you aren’t bending anything.
I appreciate the information. A basic check with a good square and feeler gauges shows the X axis top linear rail is .020 forward of the bottom linear rail. That is uniform all the way across the x axis.
I feel like I must not have done a good job squarely assembling the gantry.