Frage Z axis not square with the bed

I was told that there is a good way to align the Z axis, but haven't found the info. The bottom of a flat end mill is not parallel to the bed, so when cutting along the X or y axis, one edge of the cut is deeper than the other. To me it looks like siding on a house. Does anyone know a procedure to square it?. Hopefully a better way
than jamming tiny wood shims between the spindle and the mounting plate?

Dear Jazzdad,

I wrote a guide to level the Z axis on this thread:

www.stepcraft-systems.com/en/forum/assembly-and-maintenance/3367-spindle-bed-tramming-840-supports#42414

Doug