Since all my machine part surfaces are not machined flat, the build base isn’t perfectly square to the Z axis. This is necessary when trying to print big parts because the layers are so thin. I was aiming for holding a +/-.10mm tolerance across the build base. I measured the initial plate (when heated of course) in a 50mm grid and then placed brass shims where necessary between the build base and the build plate to make it level.
Measuring with a Caliper
Contour Map
Shiming
