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Soldering, Part 2


This is a continuation of Part 1. Techniques are described for tinning and splicing wires, splicing a lamp cord, and making connections to solder lugs. Further, instructions are given for restoring a soldering iron that has been overheated, and converting a woodburner to a soldering iron.

Tin a Wire.

This is a good place to start because it is easy to do and it is a useful technique. Often we will tin a wire and the contact to which it is to be connected before we try to join the two. Once the two items are tinned, we no longer have to worry about getting the solder to stick. All that’s required is to place the two in contact and then apply the heat. When the solder melts, it will flow out and make the connection.

So, let’s tin a wire. Strip about 1/2” inch of insulation from a small copper wire, preferably one that is solid as opposed to stranded. Apply a small amount of flux to the wire.

Next, melt a tiny drop of solder onto the tip of your soldering gun or iron. Then stroke the tip and the tiny drop of molten solder along the wire. If everything goes the way it should, the solder will flow onto the wire and give it a thin, shiny coat.

Note in the photograph above how thin the coating is. You can still see the strands in stranded wire that has been tinned.

If this is new to you, it might take several tries before you get it to work. What you must discover is, if you are using a gun, how hot does the tip need to be before you stroke it along the wire, and how fast should you move the tip along the wire?

So practice, practice, practice. If you want to solder in Carnegie Hall, you must practice. Find out how little flux you can use on the wire and have it still work. Will it work with no flux at all? How little solder does it take to do the job. What happens when you use too much flux or too much solder?

Try doing the same thing with wires of different sizes. For larger wires, you will have to move the tip a bit more slowly. Try it with stranded wire instead of solid and see the difference.

A Comment on Technique

Note in the above that the solder was carried to the work by the tip of the gun or iron. The solder from the spool was never touched to the wire being tinned.

This technique is quite different from the method typically recommended where you hold the gun with one hand and the solder in the other and touch both to the work at the same time.

There is a reason why almost all DIY solder-ers on Youtube use the two-handed approach and melt solder directly onto the connection. They don’t use flux from a can. Instead they have to melt the solder to get the flux they need which usually results in melting far more solder than what is required. And where does the extra solder go?  It drips onto the worktable or onto the floor.

There is an instance where it is appropriate to apply the solder directly to the connection. To solder a splice of two stranded wires, say 16 gauge or larger, more solder may be required than what can be carried by the tip in one pass. As the initial “drip from the tip” is applied and as it flows into the connection, add solder from the spool to the connection without lifting the tip from the wires. Don’t overdo it; it only takes a little.

Check the tip.

After practicing for a few minutes, check the tip. Ideally, it should still be bright and shiny, but a tip that has been overheated will have a dull, gray, grannular look. This is oxide on the surface of the solder that is coating the tip.

To remove the oxide, apply a tiny bit of flux to the tip and then give it a quick swipe with a paper towel (while the tip is hot). Chances are you will wipe off most of the solder, so replace it by melting a bit more onto the tip. You should always be able to observe shiny molten solder on the tip.

A dark brown residue will accumulate on the unused parts of the tip. This is the remains of flux that has burned off. It can be removed from a hot tip with a quick swipe with a paper towel.

Splice two wires together.

The diagram at right shows several ways to mechanically join two wires prior to soldering. The primary objective is to connect the wires so they will not move during the soldering operation.

The third one (3) gives a connection that extends out from the side of the wire. This projection can be reduced by folding the joint over after the solder is applied. Generally, this type of joint is avoided unless the location of the joint makes a different connection more difficult to do.

Number (6) is a simple lap joint. Its advantage is that if done carefully, the diameter of the finished joint will be no greater than the diameter of the original wire including the insulation. The disadvantage is that you have to somehow anchor the wires in position so you can apply the solder without having the wires move. I usually tin the wires individually before making the connection.

The soldering operation is straightforward. First, as always, apply a bit of flux to the connection. Then melt a drop of solder onto the tip of your gun. Touch the tip with the drop of solder to the wires and when they get hot, the solder will flow into the connection.

Comments and Observations

If the wires are large and the length of the connection rather long, the initial drop of solder carried by the tip may not be enough to do the job. In this case, add more solder directly from the spool as described above.

The solder should flow throughout the connection. If you apply the solder to the top, it should wick down to the bottom. You should not have to apply solder to the bottom in order to get solder to the bottom. If the solder doesn’t flow, there is a problem. The joint may not be hot enough, or the wires may be heavily oxidized or contaminated with oil.

The initial drop of solder melted onto the tip helps to establish a path for heat to flow from the tip to the wires.

Note that we are not depending on the flux in the core of the added solder to “flux” the connection. That job is done by the flux from the can that we applied initially.

Once the solder is applied, which should take only two or three seconds, it is important for the wires to remain perfectly stationary until the solder cools and hardens. Having the wires move during the solidification phase will give a poor joint which will look rough and gray. If they move, reheat the connection until the solder flows again.

If not enough heat is applied, you may get a “cold solder joint.” Such a joint may appear gray and lumpy, and it will not be physically strong. A good joint will appear shiny and smooth.

Make a few of these connections for fun and practice. It will be obvious when you get it right, and from that point on it will be easy. The hardest thing to learn is exactly how much heat to apply.

If you’re using a gun, don’t turn the gun ON when you first pick it up and then hold it ON continually until the joint is completed. Click it ON and OFF as necessary in order to control the temperature of the tip. For the most part, it does not need to be much hotter than what is required to maintain molten solder on the tip.

If you turn the gun ON and hold it ON for, say, 15 seconds, you can overheat the tip severely because it will get almost “red hot.” Don’t do this because you will then have to clean and recondition the tip before you can continue. It shortens the life of the tip as well.

Splice a lamp cord.

This amounts to little more than making two splices side by side, but there is one simple idea you should use. That idea is to stagger the joints. This makes them easier to insulate so that you are less likely to get an accidental short circuit.

After the connections are made, wrap the section with electrical tape to provide insulation. My suggestion is to wrap each connection individually and then cover the two with another layer that spans the section.

When twisting stranded wire, make sure that no ends of the strands stick out from the connection. Such protruding ends, when coated with solder, become very stiff and can punch through a layer of electrical tape applied for insulation. Twisting stranded wire usually does not lead to a nice-looking joint. I prefer the lap joint with pre-tinned ends.


Solder a wire to a lug.

Again, this is no big deal. The diagram at right shows four options for the mechanical connection whose main purpose is to hold the wire in place and stationary while you do the soldering. Mechanical strength of the final joint is not a concern because if the solder flows the way it should, the joint will be stronger than the original wire.

Something to consider is whether you might want to take the connection apart at a later date. If you stick the wire through the hole and then wrap it around the lug, it will be very difficult to take apart if you should ever wish to do so.

The soldering procedure is about the same as for making any other connection. After securing the wire, apply flux, carry a drop of solder to the connection, and then heat the connection until the solder flows.

When heating the connection, it’s important for the tip of the gun to make contact with both the wire and the lug. If you heat only the wire or only the lug, the solder will not bridge between the two.

Solder a wire to an alligator clip.

You can make your own clip leads by soldering alligator clips to a wire of whatever length you wish. The diagram at right tells the story.

Restoring an Iron with a Burned Tip

If you have a soldering iron with a tip that is burned and pitted, you can restore it as follows:

(1) With the tip cold, file the tip down to clean, bare metal. If you must reshape the tip, one with facets is far better than one that is rounded or conical.

(2) Apply flux to the tip.

(3) Heat the tip slowly and carefully until it is hot enough to melt solder. That is, plug in and unplug the iron repeatedly until it finally reaches the required temperature.

(4) Apply solder to the tip. Rub any spots that don’t take the solder with a paper towel or fine sandpaper until they do. The final test is whether the iron will hold a drop of solder without having it drop off. If it will, the iron is good to go.

My suggestion is to build the wattage controller (see below) and use it so you don’t burn the iron again.

Convert a woodburning iron to a soldering iron.

Because the tip of a woodburning iron is made of copper or brass, you can convert one you don’t use to a soldering iron. Just follow the procedure above for restoring a burned iron. If the tip is rounded initially, file facets on it for better contact and heat transfer to the work.

Build a power controller for a soldering iron.

The problem of having soldering irons get too hot can be solved by building a  “wattage controller” that uses a light dimmer. Instructions are given in the article, Power Control for a Soldering Iron.

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