Repairing a failed Unimat 3 Motor.
The weakness with the original Unimat 3 was the motor. It was designed to have a continuous rating of just 8 to 10 minutes and would get very very hot – too hot to touch if not careful.
The motor on my Unimat 3 packed up after 33 years of service (July 2010). I looked around for replacements, but the prices appeared just too high.
That made me wonder whether I should just open up the motor and see if it was just the brushes.
You can see by the amount of black dust and the very short brushes that are left that the brushes have worn down and nolonger making contact.
The first job was to brush out the inside and hoover up all of the dust.
The commutator was still in very good condition, so no need to get it skimmed.
I made replacement brushes from a piece of graphite that I have laying around – the brushes are simple rectangles with a hole in the end for the electrical contact.
I installed the new brushes, put the case back together and switched the motor back on.
At first the motor was a bit hit and miss, but after a few minutes of running it was back up to speed and very consistent – I assume the ends of the brushes had ground down slightly and were making better contact with the commutator.
This repair has now been working for 6 years and the motor is still going strong. You still have to be careful not to work the motor too hard or for too long as it does get extremely hot, but it is smooth and the power is just about ok.
There are alternative motors such as: Sherline DC Motor or sewing machine motors.