Having reverse available on a lathe can be quite handy, but getting it working on a 120V split-phase motor with a drum switch can be tough. Here's how to get reverse working with the motor described below.
Here's the motor:
http://www.grainger.com/product/DAYTON-GP-Mtr-4K913?s_pp=false&=
And a pic of the label:
First off, a safety notice. While this circuit isn't unsafe, it's not as safe as it could be because the neutral-line is not switched: it's always connected between the motor and the outlet with a wire nut. Now, there's a million light switches wired this way without a problem, but this could lead to trouble if the outlet is wired backwards. If that's the case, then instead of switching the hot lead you are switching the neutral and the motor will always be hot.
You can't get around this using a drum switch that only has 3 poles, like all these lathes seem to use. You can add a separate magnetic switch for the neutral. For my own use, I'm not worried, but just make sure to test the outlet first.
The motor is a Dayton 4K913BE. The switch is a Cutler-hammer 5441H27A.
This is what the switch looks like:
I could upload a picture of the bottom of the switch, but it's so full with wires I can't see how it will help.
Here's a schematic.
The dark blue lines are the factory jumpers installed in the switch. Make sure they are working. You will need to add one jumper off the hot to power the start winding as shown.
When you turn the knob, the middle terminals are connected to the terminals on the selected side.
The bottom row powers the main motor winding. It's powered the same in forward or reverse: hot to yellow and then blue to neutral.
If forward is selected, the start winding is powered by the user-added jumper from the bottom row and then it's through the red wire, through the start winding, then out the black wire and then back to terminal 5, through the centrifugal switch and then out the blue wire to neutral. When the motors reaches 75% speed, the centrifugal switch trips open to deactivate the start winding and keep the magic smoke inside the motor.
Selecting reverse reverses (surprise!) the red and black wires: hot-black-start winding-red-terminal 5-centrigual switch-blue-neutral.
This motor is not an instant-reverse motor. If you quickly turn the switch from one side to the other, it will just keep chugging away the same direction because the centrifugal switch will keep the start winding open. With a lathe with a threaded chuck, this probably isn't such a bad thing.
The wiring is actually quite logical and makes sense, it just took awhile for me to get there. Hopefully this will help someone at some point.