Hi John,
Mike (whose website that is) put me on to those cycle "computer" speedos from Wilkinsons some time ago. As he says, they have a rev counter function, unlike many other models. Mike was good enough to send me one (my local Wilkos had none in stock).
If you can only find one without the rpm function, set it so it thinks it is on a pushbike with wheels 1667mm in circumference (530mm/21" diameter), and to read in kph rather than mph. Then, a reading like 67.8 kph equates to 678 rpm. Some are only good for 100 kph (=1000 rpm), but others go up to 200 kph. That's quite some pedalling!
On a lathe, the actuating magnet can be stuck into a cork which is then stuffed into the outboard end of the spindle, as long as you aren't always working on long stock.
Andy
