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87564Short in Lathe Motor / Installation of F/R switch.

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  • Bruce .
    Jul 4, 2014
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      I had to quit work on a project, a couple weeks ago, because I was getting a 25V buzz from my lathe.  The motor appears to be the original, so may be pre-1950.  I dismounted it (without moving the lathe), cleaned it up a bit, and lugged it inside for a going-over.

      I quickly found the source of the short -- broken insulation on two of the wires in the little electrical box on the motor These wires are crammed very tightly into that little box, and I'm sure that contributed to the problem.  A temporary patch on these fixed the short.  But the insulation on all the wires was old and cracking, so I ended up stripping it off to within 2" of the motor itself, then wrapping the bare wires with electrical tape (preserving the color and number codes). 

      Interestingly, the wiring diagram showing how to connect the motor to run CW or CCW (on 120 or 230 V) was printed inside the electrical box cover.  Very handy.

      Since I had the motor out anyway, I decided to install a forward/reverse switch I'd picked up, old but never used, about two years ago.  Inspection of the switch showed it was quite simple -- one portion forming a SPDT ON-OFF-ON, but with the same two poles connected in both "ON" positions; and the remaining portion forming a DPDT (1-3,2-4)-OFF-(1-2,3-4).  The SPDT portion I used to control power to the motor.  The DPDT portion I used to reverse the connection of two wires (starter coils?) with respect to the other coils, as per the wiring diagram. I did a quick test wiring and found it worked perfectly in both directions.

      Then I had to deal with the question of how to do the installation.  Due to the very inadequate room in both the motor electrical box and in the F/R switch, and the fact that I wanted to use 14-ga wire (which seemed to be the size both on the motor and in the line cord) I added an electrical box to both.  The box for the motor was a 2x4x~2 "Handy Box", modified to fit (by notching at two corners along a 4" side and bending that side inward to "bevel" that edge.  The box  for the switch was an octagonal box that happened to have knock-outs that matched the holes on the switch.  In both cases, I used a conduit nipples and nuts to connect box to box.

      The only place I could mount the F/R switch on the lathe was under the plank the lathe is mounted to.  Although not ideal, this is not at all inconvenient.  In wiring up the circuit, I simply allowed enough cable to reach from the motor to this point.

      The only other problems I had was that the hole in the back of the headstock used for the cord between the motor and the on/off switch (which I retained) was two small for two of the 14-ga cables I used.  I solved this by drilling a 1/2" hole through the plank under the lathe and running the cord from the F/R switch through this.  The other hole I used for the power cord.

      I'm very satisfied with the result.  I've yet to use the lathe in reverse, but in the past I could have used the feature and am glad to have it.