Threading with A B phase only?

Well it is but I guess it may not be exact since it is running off an idler shaft in the headstock. Didn't think of that one, but it makes the most sense to me

Could my 7i76E handle a 24V signal on the spindle encoder interface? With 5v signals on A,B and 24v on index?

Not directly, but you can make a simple voltage divider with 2 resistors to get the signal down to a 5V level

24V index --> 1K Ohm 1W --> 250 Ohm 1/4w -->GND
the 5V signal is taken at the junction of the 1K and 250 Ohm resistors

Mtndrew77 wrote: Could my 7i76E handle a 24V signal on the spindle encoder interface? With 5v signals on A,B and 24v on index?

What type of proximity sensor is it? A 24V 3-wire NPN Prox can be connected directly to 5V logic (they act as a switch to GND, rather than a voltage output)

A little bit off topic, but...

if I add such a switch to my lathe spindle, how fast will the switch react, or better ask what rpm might it be able to count?
It would be easier than adapt an encoder 1:1 to the spindle.

Norbert

newbynobi wrote: if I add such a switch to my lathe spindle, how fast will the switch react, or better ask what rpm might it be able to count?
It would be easier than adapt an encoder 1:1 to the spindle.

It doesn't really matter as long as it is consistent at the speed that you are running at.
And spindle-synchronised moves normally happen at fairly low spindle speeds.