Rewiring watch makers lathe foot pedal

[Aaron_W]

I bought a watch makers lathe, but the wiring on the foot pedal speed control is ancient, dry and cracked with copper showing through. Easy rewire job I think so I bought some lamp cord, but now popping the cover the wiring is something I've not run across before. What appeared to simply be two sets of lamp cord one in from the outlet plug and one out to the motor side plug, turns out to be one cord.

Two wires going to the rheostat and two that are combined. The "center" two wires (of 4) are connected, in fact it appears they just cut the lamp cord in the center cut one side and pealed the wire back to attach to the rheostat leaving the other two intact.

Sorry for the crude drawing, but I think it will get the message across.



This seems simple enough but what my concern is whether or not this is actually as it appears, or if in fact maybe I'm missing something and the two "center wires" are not in fact connected as I think they are, maybe somewhere in there the two wires going to the rheostat are swapped to there is one from each side of the cord attached?

Other than direction the motor turns (then just reverse the wires if it doesn't match the directional switch on the motor) will it matter which side is which on the plug side.

Seems simple if I'm seeing things right but I don't want to let the smoke out of the motor.

 

[markba633csi]

I think you have it right, the rheostat is in series with one of the two power wires, making a loop
-M

 

[ErichKeane]

Yep, that looks right to me. The rheostat is an inline variable resistor, so it only has to be inline on one of the legs to change the circuit voltage. The other side should be a single continguous wire.

 

[Hawkeye]

When you rewire it, the wire that loops through connects to the neutral terminal on the plug. That's the wire terminal on a modern 2-prong plug and the one with the silver screw on a 3-prong plug.

 

[Aaron_W]

Thanks, I guess it makes sense, if the current is slowed on one side it still effects the whole loop. I was expecting more like a switch where two wires go in and two come out so only having two ends inside the foot pedal threw me off.

I understand the theory of electrical circuits, and have successfully done a fair bit of wiring (no fires or electrocutions yet ), but electrical work is not among my favorite things.

 

[Aaron_W]

Success! Got it wired up and the motor runs, even turns the right way on the first try.

When you rewire it, the wire that loops through connects to the neutral terminal on the plug. That's the wire terminal on a modern 2-prong plug and the one with the silver screw on a 3-prong plug.

This brings up an interesting experiment. The original plug is missing the end cover (originally cardstock most likely) so the wire attachment points are just hanging out in the open, so I bought a new but very vintage looking plug to replace it. It is an old style non polar plug, so it can be reversed in the outlet. Probably not an issue on a lamp, but it will be interesting to see if the direction of the motor changes direction depending on which way I plug it in. I suspect I may have to make a mark on the plug to make sure I always face it the same way.

 

[ErichKeane]

Success! Got it wired up and the motor runs, even turns the right way on the first try.



This brings up an interesting experiment. The original plug is missing the end cover (originally cardstock most likely) so the wire attachment points are just hanging out in the open, so I bought a new but very vintage looking plug. It is an old style non polar plug, so it can be reversed in the plug. Probably not an issue on a lamp, but it will be interesting to see if the direction of the motor changes direction depending on which way I plug it in. I suspect I may have to make a mark on the plug to make sure I always face it the same way.

1 phase motor will ALWAYS turn the right way, you have to mess with the wires inside the box to change directions. So changing the neutral/postive won't change the motor direction.

 

[Aaron_W]

1 phase motor will ALWAYS turn the right way, you have to mess with the wires inside the box to change directions. So changing the neutral/postive won't change the motor direction.

Did not know that. The motor has a three position directional switch (Counter clockwise, off and clockwise) so guess I'm all set then at least as far as the electrical stuff goes.

 

[Bi11Hudson]

Somewhere there is a cord, for a float switch I think, that has a 3 wire plug and receptical combined with only one cable out to the switch. I have one, salvaged way back in my Pipe Shop days. Would like to find a source for a few more. In essence, the 'hot' side of the plug is broken and fed to the cable, with the other side coming back to the 'hot' side of the receptical. The current one is used mostly for an older sewing machine foot control hooked to a Dremel. Anybody with a source would be appreciated. All I have found are extension cords with an extra receptical on a short cord.

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