spindle with encoder

You can't do multi-pass threading (lathe, or peck-rigid) if the index isn't 1:1 with the actual spindle.
But, for single-pass rigid tapping it doesn't matter where the index is as long a the encoder scale accounts for the gearing.

Also, it is perfectly possible to have the index and A/B phases on different shafts. A prox sensor picking up a keyway / bolt whatever on the spindle can work fine.

vre wrote:

For rigid tapping i need only index signal from spindle shaft
A-B signals can come from elsewhere the encoder is mounted that is not 1:1 ratio correct ?

forum.linuxcnc.org/49-basic-configuratio...oder?start=20#326827

As I said there, you only need the index on the spindle shaft (or 1:1 with the spindle shaft) for multi-pass threading.