lol... no worries.

 I won't be able to test the spindle w/ mach for another 2 weeks but I'll post my results then... thanks to everyone for all the helpful info.

Hi all, this is my first post and so sorry if I have missed something...
Could the signal not be "stretched" with a suitable circuit to increase the pulse length to something Mach 3 can "see".  I can think of several easy ways to accomplish this with analogue/digital/MCU circuits... a quick Google throws up loads of circuits too.

I am converting my EMI MEC Autosprint pin diode lathe into CNC and am am looking into bet way to add an encoder, I have bough an inductive sensor to start with.  The lathe spindle is currently fixed to 1 of 4 different speeds which I hope will work but if necessary I will add an inverter to the 3 Phase motor so I can control the speed.

^What main controller board are you referring to?

What mach needs is one pulse per revolution of the spindle it can be a reflective sensor or inductive proximity sensor that senses a piece of metal.  The signal from the sensor can't be very short so if you are using the reflective sensor and put a 1/16" strip of shiny stuff on the spindle that will probably not work as it will go by to fast for mach to see it.   Another thing with threading and mach you need a motor with some HP, because mach uses one pulse per rev of the spindle if you take a cut and spindle slows down a little mach will take some time to adjust and feed speed to correct for the slower spindle speed and will most likely ruin the thread unless you take a lot of very small cuts.  But if you have at least 1HP motor it will hold the spindle speed nice and steady so you can take some good cuts and have nice threads.  The motor you have now will probably not be the best choice,  it worked with the DOS system because the encoded sent out 100 or more pulses per rev of the spindle so the control software noticed the slightest change in spindle speed and corrected the feed quickly.

Hi,
yes there are many pulse stretching circuits you could use. Another possibility is a Hall sensor like:
http://nz.element14.com/honeywell/ss411p/sensor-hall-effect-bipolar-to/dp/1784734
Little button magnets glued to the spindle passing within a mm or so of the IC will cause the sensor to have an output. Note that all it requires is 0V,5V and an output, only
three wires. With a few magnets in a row you wouldn't need any pulse stretching, the magnets would trigger the output for as long as there were magnets in proximity.

Craig