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Soldering, Part 1

The Basics



Every now and then a woodturner may need to make an electrical connection that either requires soldering or for which soldering is the best option. An example that comes to mind is replacing a defective speed-control potentiometer on a Powermatic 3520 lathe. While woodturners are versatile folks, not everyone is adept at soldering. Some have never tried it, for lack of need, and others have done it but with marginal success.


This article describes the process in detail. Overall it is simple, but there are certain little details that, if ignored, will complicate matters drastically – meaning that you may not be able to get the solder to “stick.” And if the solder won’t stick, it is very frustrating, to say the least.


This article is intended for a non-solderer who wants to develop the capability and for those would-be solderers who have had difficulties or who want to improve their skills.


Now before you dismiss this as being just another “How to Solder” article, let me get your attention: You cannot solder without flux, the kind that comes in a can. Trust me. The details are given below and in Part 2 of this article.



Solder


The solder most commonly used in electrical or electronics work is an alloy of tin and lead, usually consisting of 60% tin and 40% lead. This proportion of tin and lead produces an alloy that melts at about 361 F (183 C).  


It is my impression that a lot of the solder sold at big-box and local hardware stores is inferior in some manner that I cannot fully describe. It just doesn’t act right. It won’t flow out the way it should, and it often won’t stick in a situation where a better-quality solder will. Maybe it’s different now. I don’t know because I haven’t bought any solder from such places in at least 30 years.


The good stuff can be purchased from electronics parts suppliers and Amazon, of course. Links are given at the end of this article. Unfortunately, it is usually available only in 1/2 or 1 lb spools, and it is not cheap. However, one spool represents a lifetime supply for the occasional user, so in the long run, it is not a bad investment.


The diameter of the solder makes a difference as far as ease of use is concerned. I prefer solder that is 0.031” in diameter (1/32”), rosin core. Because of the small diameter, it will heat up and melt quickly, and you are less likely to melt too much at one time.



Flux


The common metals that are easiest to solder are copper and brass. Unfortunately, the surface of both will oxidize in air, and solder won’t stick to a surface that is oxidized.


Soldering flux is a chemical that when heated reacts with the oxide and converts it back to the base metal. That is, it gets rid of the oxide so the solder will stick.


Flux-core solder has flux contained in its hollow core. A solder intended for electrical/electronic applications may be described as “60/40, rosin core.” The 60/40 refers to the percentage of tin and lead, respectively, and the “rosin” refers to the type of flux it contains, namely gum rosin which is obtained from pine trees.


Plumbers and sheet metal workers may use an acid-based flux or an “acid-core” solder. Under no circumstances should this be used in electrical work because the acid causes corrosion that over time will ruin electrical components.


Even though the concept of flux-core solder is good, that is not all you need. You will need a small container of “paste flux” so that you can apply it as needed and where it is needed. The best kind, in my opinion, is petroleum-based and contains zinc chloride as the active ingredient. I think it is more agressive than the gum rosin type. It is available at big-box and most hardware stores.


Now, for emphasis, I will repeat a statement I was known for when I taught electronics: “You can’t solder without flux.” And by that, I mean the type that comes in a can.



Components to be soldered must be clean.


The components you anticipate joining with solder must be clean, bright, and shiny. A copper wire that appears a dull reddish brown is heavily oxidized and will not readily take the solder. Flux will go a long way toward removing the oxide, but it has its limits.


Solid wire is easily cleaned with fine sandpaper. Stranded wire is more difficult to clean because each strand must be cleaned as opposed to just cleaning the ones on the outside of the bundle.


The easiest way I’ve found to do it is to untwist the strands and then fan them out across the tip of my index finger. Then take the blade of a sharp knife and scrape lightly along the strands. You will see bare, clean copper appear. Then turn the fan over and repeat for the other side. Next, collect the strands back into a bundle, rotate the bundle 90 degrees and repeat the procedure. Re-twist the strands after they are clean.


Newly-purchased wire can usually be soldered without cleaning.



Soldering Guns, Irons, and Pencils


A soldering “gun” looks a little like a gun and it has a trigger. The tip of the gun is heated by an electric current that flows through the tip itself. The temperature of the tip can be controlled by pulling and releasing the trigger as required.


The only disadvantage of a gun is that the size of the tip makes it not the best choice for working with very small components. However, with practice and a bit of care, you can use a gun to solder components that are impressively small.


A soldering “iron” has a straight body that consists of a handle and a heating element that heats the tip. Generally speaking, you can solder smaller components with an iron than with a gun. A soldering “pencil” is just a smaller version of a soldering iron.


The question now arises, is one better than the other? And I have an answer: Yes!


All the soldering irons I have used suffer from a fatal flaw. They get too hot! Further, there is no convenient way to control the temperature of the tip, short of plugging and unplugging them on a regular basis. (That is, unless you build a power controller as suggested at the end of this article.)


Isn’t hotter better? No, not when the tip gets so hot that it oxidizes the solder to a dull gray in just a few minutes. Solder that is oxidized will not stick. Over time the tip itself will become pitted and oxidized to the extent that solder will not stick to it. In this case, the tip will have to be reconditioned, as described farther down.  


Therefore, my suggestion is that a soldering gun is better than an iron for general purpose electrical work such as soldering wires to switches (even miniature switches) or soldering wires to the terminals of the speed-control pot of a PM 3520. I think it is well worthwhile to pay a little more to get a gun.



The Weller 8200


This is the gun I recommend when someone asks my opinion. (Photo above.) It is a 100/140 watt unit (the trigger has two positions, low and high) and is ideal for electrical applications. It is necessary to replace a tip after it has been used extensively because over time the solder actually dissolves the tip, which will eventually break. The tips are easily replaceable.



Soldering Stations


A soldering station is basically a soldering iron driven by an electronic unit that provides an adjustable and thermostatically-controlled tip temperature. This is the answer to the problem with ordinary soldering irons that get too hot.


Typical soldering stations are intended for working with small components such as electronic components on a circuit board or tiny pieces involved in making jewelry. They may not have the power required for soldering wires to large electrical contacts or, for example, soldering together two #12 copper wires.



Breaking in your new Soldering Device


When you unwrap your new soldering gun, it is instinctive to plug it in and turn it on to see if it gets hot. But don’t do that. At least don’t heat up the tip until it is coated with flux. A tip heated without flux or a coat of solder will oxidize quickly, and this may make it more difficult to coat the tip with solder later on.


Coating the tip, a wire, or a contact with a thin coat of solder is called “tinning.” One of the first things you should do with a new soldering device is to tin the tip. First, coat the tip with flux. It only takes a small amount because the flux will spread over the tip as it heats up. Then when the tip reaches solder-melting temperature, apply a little solder to the tip. The solder should flow out over the tip and give it a shiny coating.


If the solder fails to cover the tip completely and leaves small untinned spots, try rubbing these spots with a dry paper towel (folded to make a small pad), or rub the spot against a sheet of paper on a flat surface in an effort to get the solder to cover the spot. If this doesn’t work, use a piece of fine sandpaper to gently scuff over the spot. While doing this, keep the tip covered with flux and don’t overheat it. All that’s required is to keep the solder molten. Higher temperatures do not help the process.


Once the tip is covered with solder, it is good to go. If, while tinning the tip, a bit too much flux was applied which now may appear burned, brown, and ugly, simply wipe it off with a dry paper towel while the tip is hot. Wipe quickly; a quick swipe is all it takes.


When you have solder, flux, and a tinned tip, you are ready to do some soldering. Let the fun begin, but first, a cautionary note.



Fumes from the Flux and Eye Protection in General


During the soldering operation, some of the flux will burn and produce a bit of nasty smoke, which you should not breath. Work in a well ventilated area (moving air) or set up a small fan to blow the fumes away from you.


You should wear eye protection to prevent tiny drops of solder from being slung into your eyes. But you say, solder doesn’t tend to splatter; it may drip, but it doesn’t splatter.


OK.  Here is a possibility. You press the tip against a contact in order to remove old solder or apply new. When the contact gets hot and you are applying new solder, the tip slips off the contact. The contact springs back and slings the solder ...  right into your eyes. I’ve had it happen to me – once. From that time on, I have worn eye protection.


Solder

http://www.amazon.com/Electronic-Solder-031-lb-Spool/dp/B00DHHAZ3A/ref=sr_1_6?ie=UTF8&qid=1433110357&sr =8-6&keywords=electronics+solder



http://www.amazon.com/Kester-Rosin-Core-Solder-Spool/dp/B00068IJPO/ref=pd_sim_469_3?ie=UTF8&refRID=13A9 0CM4GWV1S6CGSW15



Flux

http://www.amazon.com/Rubyfluid-388-Soldering-Flux-Paste/dp/B0044SD3NU/ref=sr_1_1?s=hi&ie=UTF8&qid=14342178 05&sr=1-1&keywords=soldering+flux+paste



Weller 8200 Soldering Gun

http://www.amazon.com/Weller-8200PKS-120-volt-Universal-Soldering/dp/B002YDMZF4/ref=sr_1_1?s=hi&ie=UTF8&qid=14342 17993&sr=1-1&keywords=weller+8200



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