I’ve assembled my Altmill 4x2 and did the first surfacing pass. When I went to tram it afterwards, the X tram slope (parallel to the gantry) was about 0.0005 (0.3mm over 23 inches). I was able to bring this to essentially zero using an eccentric bushing on the spindle mount.
The Y axis tramming is a whole different story. The slope was 0.0094 (5.5mm over 23 inches) without the eccentric bushing. With it, I got the slope down to 0.0043 (2.5mm over 23 inches), but that still seems really high.
What could be causing this? What are the next steps to take?
Y axis tramming? Are you referring to nod on the CNC? If so I had to put like 0.012-0.018” shim stock behind my Z axis plate to fix the misalignment. It was off by quite a bit when using only the factory reference grinds on the gantry plates. Now mine is off less than 0.002” on the nod and about 0.001” on the tilt over a 10” distance from the spindle.
That’s pretty good on X. Mine was way out, I had to adjust bolts on the left side of the gantry where it connects to my plate.
Use shim stock as needed. Note there’s also 2 bolts to accomplish tramming at the bottom of the Z plate, mine were bottom’d out.
Make sure to check that your spindle moving up and down in Z is moving perpendicular to your X/Y. It is possible to tram your spindle mount, but still have the Z movement out of tram. This would not be apparent in surfacing passes, but would cut tapers in deep holes.