How to Re-wire a Potted Motor, Part 18: Re-installing the Armature and Worm

Folks, we’re now very close to the end. Having succesfully completed the actual re-wiring, your machine should now be up and running in no time. But first we have just a few more mechanical steps to get through.

Now we'll start closing the motor up, in preparation for re-attaching it to the rest of the machine. First, grab the worm, and I’ll show you a little time-saving trick.


Take one of the worm screws and insert it into one of the holes (doesn’t matter which one) and ensure that it’s properly seated. Then, screw it in a little, about three half-turns or so.

Look through the worm to be sure the screw is not intruding into the center.

Then, take the armature (double-checking that the fiber washer is on the shaft, where it’s supposed to be) and insert the armature shaft into the bearing just a half-inch or so. We stick it in just enough so that it stays in place. (Please orient your motor as in the photo above, with the motor information tag facing you, so you can easily follow along here.)

Next, grab some forceps or tweezers, anything you can use to hold the worm steady.
 

Then insert the worm back inside the housing, between the two bearings. It’s not going to stay there by itself, so you need to hold it steady in what you can only guess is the right position.

Once you think you’ve got it centered between the bearings, push the end of the armature the rest of the way in. It may require several tries to get the worm centered in the right spot, so be patient.

Note that I push from the center, so as not to touch the exposed copper wiring.

Once you feel the armature slide into the worm, push it all the way inside. Then use one if your fingers to spin the worm until the open screwhole is facing you, and you can see the armature shaft inside.

Place one finger on the worm to hold it steady, with the empty screwhole facing you, while using your other hand to rotate the armature. Keep your eyes on the empty screwhole as you do. We need to spin the armature until we see the flat part of the shaft appear in the empty screwhole.

Spin the armature...

...until you see the flat spot through the screwhole.

Here are some blow-ups so you can tell the difference:

Here, through the hole, we see the regular, cylindrical part of the armature shaft.

But here, we see the flat part of the shaft.

Now, here’s the tricky part: While keeping the hole directly over the flat part of the shaft, take the missing screw, insert it into the screwhole, and tighten it down. While doing this, keep the fingers of your left hand on the armature to hold it steady, preventing it from rotating.

It’s tricky because the worm may wobble a bit while you’re doing this, but be patient and tighten the screw slowly while doing the best you can to keep everything in place. Eventually you’ll feel the tip of the screw make contact with the flat spot on the armature shaft, assuming you've kept the worm correctly positioned, and then the worm will stop wobbling. Then, tighten the screw down quite securely.

Next, spin the worm & armature (which should be moving together by now) so you can see the other screw, and tighten that one down all the way as well.

Once that’s done, you’re good! The armature and worm are now connected.

Go on to Part 19: Re-installing the Brushes and Grease Wicks, and Refilling the Grease Tubes

How to Re-wire a Potted Motor, Part 17: Cleaning the Commutator

Now that our potted motor has been rewired and is partially back together, we need to put the armature back inside. But first we ought to clean the part of the armature called the commutator. The commutator is the series of copper bars arrayed in a ring. They are what the motor brushes make contact with, and they need to be smooth and clean so that electricity can be transmitted between commutator and brush.

The Singer manuals all say to clean your commutator with nothing more than a pencil eraser, but in practice that’s never worked for me. Perhaps it was a valid fix five or ten years into the life of the machines, but some of mine are from the 1930s and require more aggressive cleaning techniques involving a power drill and some sandpaper. The best thing to use is actually a rubber honing stick, but as I'm guessing most of you don't have access to those, I'll show you how to do this with sandpaper you can find in any hardware store.



But, by all means, first give the pencil eraser a shot; if yours come clean with an eraser, you can save yourself some trouble and skip the rest of this entry. (You’ll know it’s clean, by the way, when the surface looks like a clean penny. It doesn’t have to be completely sparkling, but there ought not be any dark spots.)

First off, here’s a Worst-Case Scenario armature. (Actually I should upgrade this to a Bad-Case Scenario armature--for a truly Worst-Case one, check out this one on the MSMO blog.) This is from a potted motor where someone apparently squirted oil directly down the brush tubes. The commutator is covered in black:

By using a Q-tip and rubbing alcohol, I’m able to get it to the state seen in the photo below. While doing it I have to be careful to use the smallest amount of alcohol possible, blotting the Q-Tips well, so that no excess fluid runs onto the wiring insulation, where it is bound to do some damage. Then I’m ready for the next step.

This is what your normal dirty armature looks like, in a machine where someone has not mistakenly injected oil into it. If it only looks like this, you can skip the rubbing alcohol step and start from here.

What you want to do is get two different grits of wet/dry sandpaper, available at any hardware store: 600 grit for the initial cleaning, and 1500 grit for the final polish.

Cut a strip off of each sheet, preferably off of the long side, that is 3/8” wide.

Then insert the shaft of your armature into a power drill, making sure the chuck is then properly tightened, for safety’s sake.

WARNING: If you do not have experience with power tools, PLEASE ask someone more experienced to do this for you. It should be a simple matter for them to follow along with these instructions. If you have never used a drill before and do not properly tighten the chuck, you are setting the grounds for a very nasty accident. So please think twice before doing this. The armature shaft must be securely chucked into the drill, with zero chance it will come free.

The next step is to use the 600 grit sandpaper. What to do is most easily illustrated in video:



You’ll note that in the video, my fingers are quite close to the drill. That is because I’ve done this a number of times and am completely comfortable with it. If you've never done this before, you may want to hold the sandpaper much further down, as in the photo below. Also note that you must pinch the sandpaper together between your fingers quite tightly.

Another tip is, you don’t have to pull the sandpaper downwards with a lot of force; you’re just trying to exert enough pressure that the sandpaper is rubbing the commutator, not grinding it into bits. We’re merely trying to wipe the commutator clean, not actually sand it. The copper comes off quite easily--too easily, as you can see by the copper dust in the photo below--and we want to be careful to remove as little of it as possible.

After our initial cleaning with the 600 grit sandpaper, we remove the armature from the drill. Next we use a plastic implement--I’m using a clay-shaping tool here, but you could probably use a cheap plastic knife--to scrape out the dark gaps between the copper bars on the commutator. This process is called “undercutting the mica.” Use caution so as not to avoid scratching the copper plates, keep your utensil in the gaps.

Here you can see some of the black crap that comes out of the gaps:

I vacuum those away with a brush attachment on my household vacuum.

Then I go back to the drill, this time polishing it with the 1500 grit sandpaper. The process is exactly the same as in the video above.

Please don't put your fingers this close to the drill unless you've done this a number of times.

Finally I hit it again with the vacuum, and now we’re good to go. It's as clean as a newish penny, not perfectly shiny, but good enough to cleanly transmit electricity.

Go on to Part 18: Re-installing the Armature and Worm

How to Re-wire a Potted Motor, Part 16: Re-attaching the Field Core

Now we’ll begin closing the motor back up. Please orient your motor as shown in the photo above, which is the way we had it in Part 15.

Then note that there will be a potential problem in closing it up, as seen below:

If we’re not careful, the bottom motor lead will block one of the screws that attaches the field core to the rest of the housing.


To prevent this, we insert that screw prior to closing up the motor.

Insert the screw all the way, and tuck the motor lead behind the screw.

Then, as we begin closing the motor, we ensure that wire stays behind the screw.

The tricky part is that we must guide the screw into the screw hole. This may take you a few tries.

Once you feel you’ve got the screw properly seated against the hole, test it with the screwdriver and see if you can tighten it.

If it does not want to easily tighten, STOP and try re-seating it. If you get the screw in at an improper angle, you can strip the threads, which is bad news.

Once you feel the screw going into the hole properly, begin tightening it--but don’t tighten it all the way. Get it up to about the point shown in the photo below, leaving a gap between the core and the housing.

Then we turn to the other screw we need to do on the other side.

Don’t forget this side is the one that has the motor information plate. Hold that in place.

Then insert and begin tightening the screw on this side. But again, don’t tighten it all the way; leave a gap, as on the other side.

Now we look inside the motor. We want to be sure there are no errant wires sticking out, which would interfere with the armature.

Here you can see the brush lead is neatly tucked away to the side, as it should be. Check to see that the other side looks the same.

Once we’ve confirmed there is no wiring sticking out, we go back to the first screw and tighten it all the way.

Then do the other side.

And that’s that, the motor housing is now ready to accept the armature again.

Go on to Part 17: Cleaning the Commutator

How to Re-wire a Potted Motor, Part 15: Soldering On New Motor Leads

Now we’re finally ready to solder new motor leads on. Again, please ensure that your motor is oriented exactly as in the photo below, to ensure my explanations of “top/bottom” are correct:

Motor oriented with field core at left, bobbin winding assembly at top right.

Ready? Let’s begin.



In Part 13 we cut the old motor leads, leaving the top one an inch long, the bottom an inch-and-a-half long, as shown here:

The top lead is 1" long here.

This is the maximum length we can leave them and still fit everything inside; we’ve cut them to this length to give you first-timers an opportunity to braid the new wire on without the leads being impossibly short.

However, the ideal length is really about 3/4" or less for the top motor lead, and 1.25” for the bottom motor lead. Here’s a photo of a different motor to which I’ve cut the top lead quite short:

The top lead is 3/4" long here. Harder to do, but better.

Braiding a new wire to a connection that short can be challenging, particularly when you cannot quite get your fingers around the shorter lead coming out of the winding. It requires a fair amount of practice. If you feel you’re up to it, go ahead and cut the leads to this ideal length, but be aware there’s no going back.

In any case, get those leads as close to the ideal as you’re comfortable with, then let’s get started.

Cut two 8-inch pieces of new 18 AWG wiring. (Use different colors, obviously. I prefer red and black because those correspond with the colors on the terminal body where they will attach.) Strip the ends to a 1/2-inch or 3/4-inch, depending on what you became comfortable braiding during your soldering practice.

Don’t forget to individually braid the ends.

Then, braid the BLACK wire to the BOTTOM motor lead, and the red wire to the top lead.

Set up your Helping Hands, placing at least one of the alligator clips between your joint and the winding. This is so the clip will act as a “heat sink,” absorbing the heat from the soldering iron instead of letting it flow into the winding. Be mindful that the clip may get quite hot, so don’t forget to let it cool before you touch it.

Then, solder away, as we practiced in Part 3.

Next, cut some of the 1/8” heat shrink tubing to whatever length will cover all of the exposed wiring, going right up to the winding. Be sure to cut the heat shrink tubing so that just 1/8” of it will overlap with the existing insulation on the new motor leads. (Don’t make it overlap any further than that, or it will give us trouble later.) Then slide the heat shrink tubing onto each motor lead from the tail end.

You may remember that I left some of the old insulation on near the base of the bottom motor lead. Here you can see that, in addition to covering the new joint with the 1/8” stuff, I’ve covered the thicker leftover insulation with the 3/16” heat shrink tubing, as the 1/8” would not fit over that section.

In the photo above, you also see that I’ve stacked the motor even higher up with more blocks, so I could comfortably fit a lighter beneath it. It may look precarious, but rest assured I’ve checked it for stability, so the whole thing doesn’t come tumbling down as I’m working on it.


Once I’ve finished the heat-shrinking, I take the motor off of the blocks for the next step.

Now we tie the underwriter’s knot that we practiced earlier.

Since we practiced “moving” the knot down the wiring before, you should have no problem getting the knot exactly where you want it. And where you want it is right up to the heat-shrink tubing.

Heat-shrink tubing is stiff and doesn’t bend well, by the way, which is why we made sure it didn’t overlap too much with the insulation on the new wiring. If we made that mistake, that would move our knot further out than we want it, which might prevent us from closing the motor.

Get the knot as tight as you can get it, but be careful that you don’t place a lot of stress on the motor leads where they go into the winding. That is the most vulnerable part of this operation.

Next, take some of the larger, 3/16” heat shrink tubing and cut a piece exactly 3 inches long.

Use it to cover both leads...

...sliding it all the way down to the knot.

Then heat-shrink it with your lighter.

Now it's heat-shrunk. Don't worry if the tails of the wiring are going all over the place, we'll sort that out later.

Finally, route the wires from the inside of the motor out through the grommet. With my left hand I keep my fingers on the base of the motor leads, to prevent stressing their connection to the windings, while I use my right hand to thread the wires out through the grommet hole. (My right hand is absent in the photo because it's holding the camera.)

Now we're in good shape. But don't connect the field core to the motor housing just yet, there's a trick to it we've got to cover.

Go on to Part 16: Re-attaching the Field Core