Hi, I recently bought a Union Graduate woodturning lathe with fitted electronic speed control.
The unit has a digital read out which ascends from 1 to 50
Problem is I don't know what the actual speed of the lathe is i.e. rpm
Is there a way to measure the actual rpm so that I could create a table of say digital read out is 20 then this would = 1000 rpm or whatever.
cheers
jez
"jez" wrote in news:1126127011.fabcb76d7da5d7af0984099970f656e0@teranews:
There are a variety of ways. You could put a scope on the drive output to measure the frequency combined with the number of poles on the motor which you can get by starting at a low frequency that you can measure with a stop watch. There are many different kinds of mechanical tachometers designed to do just this job. There is a cheap one called a Vibra-Tak which I bought 35 years ago that is an adjustable cantilever pendulum. You adjust it until it shows the maximum vibration, which is when the cantilever is in resonance, and read the rpm off a scale on the device. There are also a bunch of optical designs. You could use a strobe driven at particular frequencies and turn the lathe up until it appears to stop. You could find a car with a generator and a tach, disconnect the voltage regulator, and plot voltage out vs. rpm, then pull the generator and drive it with the lathe. You could make a spool to hold in the chuck, take a fishing reel with a known amount of line, and measure the length of time it takes to spool up all the line. You'd have to make some assumptions about the mean wrap diameter, but you could probably get close enough for the purpose. I'm sure there is a method that involves a cat and a friend with perfect pitch, but I just haven't quite pieced it together yet. Have fun.
Dear jez:
There are little wheeled "tachometers" used for measuring belt speed on a conveyor. You might be able to use one on some large, constant diameter feature on the lathe, and get to rotational speed that way. (Try McMaster Carr?)
You could put a counter on some feature that actuates the counter once (or more) per revolution. Run it at constant speed, for some minutes, and get it that way.
You could find out the maximum hertz the inverter will make, and simply infer the speed based on the motor nameplate.
David A. Smith
A stroboscope or a non contact tach or for that matter a contact tach.
Or you could look at the motor - an induction 60 Hz motor would go slightly slower than 1800 rpm or 3600 rpm.
Then, if there is a drive belt you could measure the pulley sizes?
Or buy a long screw rod and run a couple of nut on one end.
Place a rubber foot on one end of the screw rod, and/or fix it to the wood orr the face plate or the chuck.
Time how long the nut takes to run a measured length of the rod. Count the thread turns.
Brian Whatcott Altus OK
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