Hi All, one thing a lot of people don't know is that single phase motors, (as are fitted to the majority of the cheaper home type lathes) are not designed to be stopped and started more than a few times per hour.
This is not a problem with 3 phase maotors.
The fact that the manufacturers fit single phase motors with on/off switches for stopping and starting is because it's too expensive to fit a clutch in the drive mechanism which allows the motor to keep running.
Every time you hit the start switch the start windings are engaged, and as they are only designed to start the motor and bring it to synchronous speed and then drop out without burning out, it doesn't take much imagination to realise that after a few starts the windings get hot.
Most, but not all, single phase motors are designed to run continuously, but this doesn't mean they can be stopped and started frequently.
I overcame this problem by fitting the electric clutch from a cars airconditioner pump to my Colchester Bantam lathe, and this allows me to keep the motor running continuously and stop and start as many times as I want for measuring purposes.
The clutch is powered by a 12 volt transformer with rectifier for DC, and only requires about 2 amps to power it.
I've also fitted an electric clutch to my 1-1/4" capstan lathe and this usually runs for 6 or 7 hours at a time.
The motor on this lathe is a 3HP 3000 rpm single phase induction motor.
The electric clutch will handle quite a few horsepower and at high speeds as well without a problem.
Most car wrecking yards throw the aircon pumps away as scrap because they're too expensive to repair when they fail, but the electric clutch on the pumpshaft end is usually still good, and the whole assembly can be had for a few dollars, just don't say why you want it or the price goes up.
Ian.  |