Y-axis bracket. Mill works again!
Day 1 Design.
Day 2 bore out a single hole.
Day 3 refine design
make a tool to hold the giant tap (1.302″ in shaft diameter to tap a 1-9/16″x18TPI hole)
tap the part.
Day 4 measure everything again
refine design
Mill out the part by hand (done horribly but works)
Disassemble mill
install newly machined bracket
reassemble mill.
Mill’s measurable backlash = 0.0005″ [on that axis]
I’m happy now.