Multi-purpose lathe spindle mount

When the motor died on my 12" x 37" gap bed metal lathe I took the opportunity to make a few planned upgrades including converting the lathe to a variable frequency drive and 3 phase motor.

Of course that meant that I would need to either manually calculate speeds using the motor frequency and selected gearing or I'd need to install a tachometer. I went with a tachometer so in future I can also have an Arduino calculate the workpiece surface feet per minute and the lathe feed rates. The tachometer display and speed control potentiometer are housed in a control box on the head stock. See link for those components https://www.thingiverse.com/thing:5178575

A tachometer requires mounting a magnet on the spindle and designing a bracket for a hall effect sensor. The best place for the bracket and sensor where it wont interfere with things on my lathe is on the outboard end of the spindle. This also happens to be where I wanted to install an indexing system.

This meant designing a mu