by Rich Schneider, Guest contributor to CSG
Usually the hardest part is figuring out how to hold a piece in place so you can solder it. Once you have this obstacle overcome you have won the biggest part of the battle.
There is nothing like good old practice. Make sure you have a good - hot - iron, (or gun) fresh resin or flux, clean, fairly new solder. Don't use solder that you have had laying around for the last 10 to 15 years or so, it will be oxidized and will give poor results.
Make sure the items you want to join together by soldering are clean. Have a clean, tinned (freshly solder covered) iron tip, heat the parts to be soldered quickly and apply the solder to the parts, not the iron and get the iron and solder out of the work area as soon as possible and allow the soldered joint to cool. The whole idea is to not cook your parts to death!
After you practice enough you will gain experience which will tell you the following: 1 - How hot to have your iron, 2 - how long to apply the heat, 3 - how much or how little flux to use, 4 - How much solder to apply while soldering. This step can be controlled by using solders of different diameters.
Solder is available in many diameters and combinations of soft metals, with different melting points for different alloys. They come with or without flux cores of various types. Some solders contain lead while some do not. Some of the better varieties contain silver alloys and require a little more heat than the lead types. There are also solders that will allow you to use a soldering iron to solder aluminum to copper, brass, etc.
If you are in doubt about what solder to use on something the best place to ask for a recommendation is your local welding supply dealer. This is where the experts should be when it comes to the technical stuff about solders. Your electronics store will not have 95% of the info you really want.
If you are soldering steel rails, you should make some provision to be able to clean your rails with really clean hot water after soldering. The fluxes that work best with steel are somewhat corrosive and will cause your rail to rust over time unless it is rinsed off.
I have soldered Gargraves stainless steel rail using this method to attach wiring to it. Stainless requires an extreme amount of heat for any amount of success so unless you have all day to play and a lot of patience, don't attempt it. I did not enjoy doing it and would not have tried it if my tracks had been removable.
I recommend cleaning the rails where they are to be soldered with a small wire wheel in a Dremel tool, although I don't think this step is really needed unless it is tarnished or rusted.
If you suspect there is a coating of anything on the rail, use a suitable solvent and a small stiff bristled brush to clean it off.Acetone or lacquer thinner will do an excellent job but make certain you are in a well ventilated area and away from fire, flames and sparks. These chemicals are dangerous to your health and explosive not to mention flammable! So do this part out of the house, work shop, or train room and for Gods sake DON"T SMOKE!
After the rails have dried, assuming you cleaned them with a solvent, put a generous coating of your favorite soldering flux or acid on the area to be soldered, heat it with your iron, then apply a second application of flux along with a small amount of solder. The first flux only heating is a cleaning step. The second heating with solder and flux is the tinning step. You can dip the end of your solder in your flux before applying it. Sometimes this is better than a brush or other applicator. Don't be afraid to slide your soldering iron or gun back and forth on the surface you are tinning. sometimes this helps remove that invisible something that is causing the solder to not stick.
This should tin the rail (apply a solder coating to it). Remove the iron, check it for spots without solder. At this point all you want is a thin coating of solder, but you want a continuous coating. If there are any voids in the coating, reapply the hot iron and a little more flux to the void, no more solder. After it looks good reapply the hot iron and your solder to fill with as much solder as you need to make the bond. Do not use a rosin or resin cored solder. Use a solder with an acid core or no core at all.
The absolute best location for you to put the tip of your soldering iron or gun, provided everything has accepted the solder well, is at the underside of the joint or connection being soldered. Heat rises, so in theory and practice the heat source should be underneath your work. Unfortunately this is just not always possible.
If you practice enough and remember clean, hot & fast, soldering will be a snap!
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