Rigid tapping/spindle synchronized motion with only motor encoder

Spindle.revs is just the spindle position, it normally counts up (or down)
continuously, so it may count to any number, and is reset by index
at the start of spindle synchronized moves, so I think the only difference
with your 1 index per 2 spindle revs system is that LinuxCNC will have to wait
longer on the average for index to occur (from waiting 0.5 turn average
to 1.5 turns average)

Thanks for all your input. The motor is not on the spindle yet, but I can give it a shot running on the bench.