Monday, December 12, 2011

How to Re-wire a Potted Motor, Part 2: Tools/Materials Required for Soldering

You only need the one in the middle

If you can learn to solder, you can breathe new life into that basket-case 15-91 or 201-2 you’ve got with the rotted wiring insulation. If you’ve mastered the wire braiding we went over in Part 1, now you’re ready to try soldering. But before we get to that, I’ll describe the proper tools required, because I don’t want you to overeagerly buy the wrong items first like I did. Read this before you spend any money.

Also consider this: The soldering process requires holding the tip of a soldering iron against your wire joint to heat it, then adding solder. It requires a fairly steady hand--you may have to hold the iron steady for 30 seconds or longer with some precision--so if you have grip issues or arthritis, you may find this challenging; please read the “arthritis” paragraph at the bottom.

Tools and materials you’ll need:


- Soldering iron
- Solder, 63-37
- “Helping Hands”
- Old sponge
- Eye protection


- Soldering iron stand
- Respirator

Soldering Iron
Soldering irons come in two different forms, “pencil-” and “gun-” shaped. They also come in different wattages.

After trying out three, I recommend the 40-Watt pencil-style soldering iron. The pencil form factor is easy for me to hold steady, and the wattage is adequate for the task. Radio Shack sells one for $10.99.

The 25-watt pencil soldering iron I bought first is too underpowered. It takes up to two minutes to get the wire hot enough to accept solder.

The 150-watt gun soldering iron I bought second is overkill. It gets very hot very quickly, but is a bit on the heavy side and difficult for me to maneuver, especially when working close to the motor leads.

Solder comes in a bewildering variety--lead-free, rosin-core, 60/40, 50/50, and in different diameters. What you need is 63-37 Rosin-Core Solder in 0.50” diameter. Radio Shack sells a 1.5 oz spool, which is plenty, for $6.99. (As far as I’ve seen in their stores, that’s the smallest amount they sell.)

“63-37” means it’s 63% tin and 37% lead. This specific percentage is what Singer 221 guru Graham Forsdyke’s motor specialist uses, and he used to work in the Singer factory in Kilbowie, so I’m sure he knows his stuff.

Lead-free solder requires extremely high temperatures to melt, which is why I don’t use it. The other type, rosin-core, melts faster, which is what we want.

“Helping Hands”
You will find this tool invaluable. It’s just two moveable alligator clips attached to a small iron base so it doesn’t move around. When you solder you’ll have the soldering iron in one hand and the solder in the other, so you’ll need something to hold the wires steady, particularly when we get into the actual motor.

I did read about one woman using stacked tunafish cans to sandwich the wires in place while she soldered. I can’t recommend or naysay this method because I’ve never tried it, I’m just throwing it out there.

You should be able to find Helping Hands at your local hardware store or at an art supply store. I bought mine in a local jeweler’s shop in NYC for about $10. There is also a variety for sale on Amazonat cheaper prices, but be sure to read the reviews to avoid the crappy ones that tip over.

Old Sponge
You’ll need an old sponge to periodically wipe the soldering iron tip on while you solder. You’ll also need something to weigh one end of the sponge down, like a brick or a glass bottle filled with water or something. This will all become more clear in the next entry, when we actually get into soldering.

Eye Protection
Chances are slim that something hot will fly up into your eye when you’re soldering, but like most of you, I earn my living with my eyes. If there’s a 0.00001% chance something is going to fly into my eye, I make sure they’re protected. If you don’t already wear glasses, safety glasses are a couple of bucks at a hardware store.

Soldering Iron Stand
I say this is optional because most soldering irons come with a little dinky stand (below) that you can prop the tip on, like a chopsticks rest, to keep from burning your tabletop.

If you’re on a tight budget you can make do without the soldering iron stand and just use the dinky one. But I like using the stand because it’s convenient and has a little place to hold a sponge. I got it at Radio Shack for $8.99. There are also a bunch of these on Amazon.

Solder fumes are toxic--it’s gaseous lead--and while a whiff or two probably won’t kill you, breathing it in all the time probably will. If you’re going to solder a lot (as we will for practice), and if you have to do this indoors and you live in a windowless apartment like I do, consider getting a respirator. Otherwise do it next to an open window or if you live in a nicer climate than I do, outdoors.

I bought a respirator years ago because I needed it for various woodworking, sanding and painting projects. I hate wearing it, but I force myself to since I don’t have health insurance. Mine is a model 7501 made by 3M, which comes in different sizes, so I could find one to fit my small face. If you decide you need one, your local hardware store will surely have it. If not, here you go.

For Those with Arthritis
If you have arthritis or grip issues and want to guess if you’ll be able to solder without wasting any money on a soldering iron first, try this. Take the heaviest pair of scissors you own, like a pair of Ginghers or similar. Hold them like a pencil in your main hand, about midway up the scissors. With your other hand, grab a ballpoint pen and hold it like a pen, but up high on the pen. Then touch the tips together, and see if you can keep them touching for about 30 seconds.

It doesn’t have to be exactly point-to-point, but see if you can keep the tips in general contact with each other. This will give you an idea of the manual challenge that soldering demands, and will hopefully help you decide if you’re up to trying it.

Thanks for your patience, as I’m sure many of you are eager to jump right into soldering. But if I save even a few of you from wasting money on the wrong soldering iron or wrong type of solder, then I won’t feel like such a dope for blowing my cash on those things.

Next we’ll get to the actual soldering.

Go on to Part 3: Learning to Solder


  1. I really like my little Weller 25 watt. I have a bigger one from RS but I can't get the wire hot enough.... The orange one in the photo

    Thanks for this great tutorial...

  2. Love your blog! Thank you so much for taking the time to post pictures and detailed instructions. I have been wanting to learn how to fix/repair my vintage machines, but haven't known where to start. And they keep following me home. . .

  3. Is "Solder Wire 63/37 with a Rosin Flux Core .032" made by M.G. Chemicals equivalent to the one you recommended?
    Thank you for sharing the purchasing information.

  4. Hi Miriam, absolutely you can. In fact the thinner .032" diameter will probably melt faster, which is good. I use .05" diameter because it's all I can get near my location.

  5. Thanks Rain.
    I read/watched your next post and learned my soldering technique has been wrong. I thought the iron was supposed to touch and melt the solder. No wonder I had so much trouble! Thanks for describing everything in detail!!