Hi,
For what it is worth I will share my experience on a similar vein.
I have a spindle index provided by a hall effect switch triggered by a rare earth magnet embedded in the aluminium spindle pulley.
So it is pretty much similar to yours, by a slightly different path.
It provides a very good and accurate RPM reading and I wanted to see if I could thread with it alone.
With some help from Andy I set up the .hal so that the output was fed to encoder.0.phase-A and ..phase-Z and EMC thought it had all it needed for threading.
In practice however it just didn't work. Despite giving it a long feed in to stabilise Z axis speed before reaching the thread, after a few passes, if that, the Z feed would stutter as it struggled to match position with index and errors occurred.
So I made a 120 hole indexing disc, used with an optical switch. Again with Andy's help, I built a comparator circuit to give a clean on and off signal, which is very necessary when you are talking about 3mm holes with approx 3mm spacing between them turning at several hundred RPM
The result was perfect threading and a smooth perfectly timed Z axis movement.
I have pasted the relevant section from my .hal file along with the comment I made at the time after the first test.
If this is of any interest I can forward the remainder of my setup.
regards
##########################################################################
# Had several tries to get proper index for threading
# Eventually used a 120mm PCD 120 hole disc, with optical sensor through
# comparator, for clean on/off
# spindle index is still provided by a single rare earth magnet via a hall-effect.
# At first test, cut a perfect 1.5mm pitch thread using a tool steel cutter
# presented at 90deg to the billet!
# Optimal pulses appears to be around 120, 60 works but 120 is better, 240 is too high
############################################################################
setp encoder.0.position-scale 120
setp encoder.0.counter-mode 1
net spindle-position encoder.0.position-interpolated => motion.spindle-revs
net spindle-velocity encoder.0.velocity => motion.spindle-speed-in
net spindle-index-enable encoder.0.index-enable <=> motion.spindle-index-enable
net spindle-index parport.0.pin-11-in-not => encoder.0.phase-Z
net spindle-pulse parport.1.pin-10-in => encoder.0.phase-A
