Industri Repair: How to Re-wire a Potted Motor, Part 20: Hooking It All Back Up

Now we’re at the final step to getting your machine back up and running!

Start by sliding your newly-renovated motor onto the shaft.

Tighten the two motor mounting screws securely.

Then, unscrew the terminal body. Note that I’ve tucked the two motor leads behind the terminal mounting bracket. This is so that we can determine the proper length to cut the tails.

Now we’re going to make new connections on the ends of the wires. As we went over in Part 4, you can either make your own eyelet and solder it, or use crimp-on connectors.

Option 1: Self-Made Eyelets

The self-made-eyelet-and-soldering route requires plenty of wire, which is why we’ve left the “tails” of the motor leads so long. You’ll need to calculate where to cut the wire such that you’ll have plenty of material to form your ring. I suggest measuring and practicing on a scrap piece of wire first, so you can be certain where to cut and strip in order to produce a ring that will still reach the post it needs to connect to in the terminal body. If in doubt, cut too long, not too short!

Option 2: Crimp-On Connectors

Here I’m going to do crimp-on connectors, which requires less length and is easier for me to execute. I generally determine where to cut by letting the terminal body hang naturally, supported by the lighting wires that are still connected, and then drawing the motor lead over the knob that it will fit under. I then pinch the wire to the side of the knob furthest from the motor, as shown in the photo, and cut there. This will make the final wire long enough that I can comfortably manipulate it into place.

Next I strip the wire ends to the length required for a crimp-on connector, just 1/4" or so.

Then I gather the connectors and, very important, I immediately cut two pieces of 1/8” heat shrink tubing about 1/2" long.

I slide the heat shrink tubing onto the wires first…

…and only then do I attach the connectors and crimp them on.

Then I slide the heat shrink tubing down into place, as seen below. You’ll notice that now I’ve pulled the motor leads OVER the terminal mounting bracket.

I’ve done that so that I can get the wiring a good distance away from everything else, to comfortably fit a lighter under the heat shrink tubing.

Now they’re heat-shrunk and ready to go.

Re-Attaching the Wiring
When the ring connectors are ready, tuck the wiring back UNDER the mounting bracket, in their final position. Pull the red and black wires over to their appropriate posts on the terminal. (Here I’m working on a 201-2, which has a light switch, and you’ll observe I’ve had to thread the black wire underneath a different wire that arches over it, connecting the light switch to the red post.) If you have a cabinet-mounted machine, connect the foot controller wires too, even if the machine isn’t in the cabinet yet. We need to do some testing.

After connecting the right wires to the right posts, we tighten up the thumb screws. Get all three of them as absolutely tight as you can with your fingers.

Now it looks like this. Be sure you’ve got the motor leads tucked BEHIND the bracket…

…then screw the terminal back into the machine. Do NOT overtighten this screw. The terminal body is made of plastic and easy to break. You only want to get it tight enough that it doesn’t wiggle around when you plug the cord into it.

I’ve grossly overexposed the next shot so you can see how the motor leads come down unobtrusively from the motor and disappear behind the mounting bracket.

Now we’re at the moment of truth!

Running the Motor

I plug the machine back in without re-attaching the handwheel, because I want to run the motor with no load--that is to say, not powering the rest of the machine--to ensure that it runs smoothly. This way if the motor doesn’t run, I know it can only be the motor that is the problem, and not some jam somewhere else in the machine.

Then I get the button controller up on the table. (And obviously, you should not stick your fingers inside the motor housing for any reason!)

Here are the results:

That’s the sound of a potted motor 201 running with no load. Sounds very different than when it’s connected to the rest of the machine, no? Sort of reminds me of a jet engine. I’ll continue running it for a few moments to ensure it runs consistently. And if you’ve inserted new brushes, you ought to run the motor for five minutes or so anyway, to wear the brushes in.

Warning #1: If you run the motor as I’ve done in the video above but it sounds different--for example, if it buzzes first and starts haltingly--STOP and unplug the motor immediately.

Warning #2: If you run the motor for a few minutes and it gets warm, that’s fine, particularly if you’ve been running it full tilt. But if it gets HOT, please STOP and unplug the motor immediately.

Both of those warnings are signs that something is wrong with your motor, either in the field core, the windings or the armature itself. And that something might be dangerous, which is why we ought to unplug the machine immediately. Sadly, those problems are currently beyond the scope of this blog.

But hopefully, everthing has turned out fine.

Re-attaching the Handwheel

It’s my habit to unplug the motor when I re-attach the handwheel, though strictly speaking it’s probably not necessary.

The next thing I do is use the grease syringe to dab some droplets of grease around the perimeter of the fiber gear. People often over-grease these things, but you really don’t need to go nuts with it.