I've bought an inexpensive frequency module off Ebay (search on "digital frequency meter" if you're interested - =A37). Irritatingly it comes without any guidance for use but I rigged up an LM555 to give suitable pulses and have got it reading Hz or rpm by changing a jumper.
The lathe is an elderly Wadkins - sturdy CI structure with a low mounted motor and a four block V belt pulley - very similar to many wood turning lathes of 30+ years ago. It has a 3ph motor driven by an inverter.
I'm looking for suggestions on how to get a suitable signal off the pulley block or spindle.
Thanks for any help