Hey Keith, hey all,
the first solution to the “65 mm spindle bumping the stepper cage problem” I saw was on thingiverse.com and it consisted in 3D-printing two taller stepper mounting blocks:
This allowed to move up the plate on which the stepper sits, instead of only the stepper. That meant you needed longer bolts for the two mounting blocks, not for the stepper itself. The rest was the same, shaft extension and 2nd shaft coupler.
But you are much better off with the solution linked in the other post above, if it’s okay to file a bit of material away from the stepper mounting plate as shown on the pictures.
One advantage of this solution is that the position of the center of the router shaft stays very close to the Z rails which means, less leverage force, and thus less deflection under load when milling. And when you update the milling motor, you can go to a 65 mm spindle. Note that for this case lifting the stepper by 12 mm will not be enough! I would choose more right away now you’re at it.
Lifting it by 50 mm sounds reasonable, possibly a little more could be better, but I don’t know which value would be the best as I don’t have a 65 mm spindle, only a 80 mm spindle. It also depends on whether you take an air-cooled spindle (seen above) or a water-cooled spindle. The latter are longer so with lifting by 75 mm (3 inches) you are on the safe side.