Saturday, June 27, 2015

Original Lathe AC Motor Rebuilt

I broke the lathe.  Yes, I broke it that fast.  I was turning a pen for a neighbor, and plugged it in for some final sanding, there were some arcs and sparks (both in the motor and in the power cord end that I was holding), and it stopped working.

I started looking at DC motors.  Here's what I needed - a motor with a 1/2" shaft, 1/3 Horsepower, and (preference here) direct current with variability in RPM.  I finally gave up and decided to crack the original motor, trying to locate the start capacitor in case I could track a new one down.  Don't get me wrong, there are motors out there, but they were all priced in the $300-$800 - and I wasn't plopping that kind of cash into the Ebay ecosystem.

Model:Dunlap (Sears) model 15.4624
Speed:1750 RPM
Shaft Size:0.5" (or 1/2")

So, I cracked it open.

I noticed a few things :

  1. It had a switch (yeah, I didn't see that before because it was on the back side of the motor).
  2. I moved on and found where the wiring went into the casing had worn out, and the wires (made of aluminum) had been exposed to the metal casing - that would be an additional cause of the arcing and sparking.
  3. It was DIRTY!  I grabbed the air compressor nozzle and cleaned it out quickly, but made a nice mess of the back patio in short order.

I found that there wasn't a start capacitor in this motor.  It is actually a mechanical assembly.

I also realized that there were oiling channels for the motor bearings, on each end of the case.  Thinking they were plugged with old saw dust, I grabbed the air nozzle again and tried to blow them out.  Turns out they weren't plugged, but it's some sort of a sponge in there to keep the oil so it would channel into the bushings/brearings.  There are grooves on the inside of the casing angled in such a way to put oils around the bearings.  Quite ingenious, if you ask me.

After soldering a replacement power cord into place (and fixing a few other things while I was at it in the electrical system), I buttoned it all back up, and plugged it in... success! Proud to have a working original motor connected to the lathe still, costing $15 of repair (for the replacement power cord, which had gouges in it exposing the aluminum wire and making it a bit dangerous). I get my man card back again.

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