My Hercus seems a little slow for cutting steel, so I wanted to check the rotational speed. Could have borrowed an optical tacho, but a cheap tacho display with sensor is $14 or less from eBay, so I thought I would hook one up.


What Pic Note
Buy the gizmo, work out the wiring.

Chinese symbols on the 5 pins, and no doco.

Had to search the web for part number,
to find someone else's pinout diagrams		 IMG_0454.jpg Sensor has 3 wires,
power is 2 wires,
but pin4 on display unused!!!
Sensor uses a small magnet.
Lost the round one that came with it -
flew off somewhere when testing on a
high RPM spindle motor - had to improvise.
Part of rare-earth magnet from a disk drive.

Try to work out where to put it.
Spindle take-up nut?





Bull nose pin thingy?		 IMG_0455.jpg

IMG_0457.jpg		 Smashed up the
magnet holder
with a hammer.
Got a tiny little flat triangle!
Seems to work OK on spindle take-up nut IMG_0456.jpg Middle speed ~350RPM
Thought I would check the motor speed also IMG_0458.jpg Different magnet fragment
but it was a bit more unreliable... IMG_0459.jpg

IMG_0460.jpg

IMG_0461.jpg
turned magnet around and got expected RPM IMG_0463.jpg




So, I might make a little box and mount this near the rear belt pulley, but I gotta work out a power supply
(this lathe motor is 3phase without a neutral, so local 240v transformer is a challenge)



Anyway, with my current motor pulley, these are my spindle speeds...

Belt position back geared straight
Right: 38 RPM 207 RPM
Middle: 66 RPM 355 RPM
117 RPM 629 RPM



"Textbook of turning" says 750RPM max., so I guess I am close to the original speeds, but a bigger motor spindle would be handy
Attached Images




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