Soldering

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Introduction

What is soldering? Soldering is one of many ways of joining together two or more pieces of metal. In this instance the metal is joined together by melting an alloy, soft solder (usually made up of 40% lead and 60% tin) so that it forms a thin layer between the two surfaces. The temperature at which the solder melts depends on the amount of tin in the alloy, the more tin the lower the melting point. For the purpose of this article, I shall be trying to explain this technique using brass as the metal to be soldered. Depending on the type of work you need to do, make sure you are using the correct type of solder and flux.

Solder

224 degree melting point for general purpose soldering.
145 degree melting point for detail work.
70 degree melting point for white metal only.

There are many types of solder available but these are the ones I get the best results from. They are all produced by Carr’s and can be found in most model railway shops.

Just a little note about the electrical solder, the type that has a flux core (multi-core). This is great for electrical work but not at all suitable for soldering brass or copper together (more later).

A word of warning. Some of the contents in solder may be harmful, always wash your hands after handling solder.

Flux

When soldering, flux is one of the main players in the operation. It is made up of diluted Phosphoric acid and should be handled with care. Again this comes in many shapes and sizes, so it is really up to the individual which type you use, whether it be paste or liquid, I use Gaugemaster Brass Flux. See Gaugemaster. It costs around £4.75 and will last for ages, unless of course you knock the container over!

Flux is used to help clean the various oxides from the mating surfaces. It also helps the solder to flow more freely along the joint. If at any time you are not happy with a joint, always apply more flux to help the iron melt the solder.

Tools

You don’t need a great selection of tools to achieve a good soldered joint; basically all you need is as follows:

1. A selection of needle files.
2. Something that is abrasive, i.e. Fine Emery paper, Green kitchen pad (new) or a Fiber Glass brush, The last item can be obtained from Maplins for only a couple of quid. They look very similar to a retracting pencil. A word of warning about fiber glass brushes, the tiny particles that are left over are very sharp, and for days you will feel them in your fingers, they are also very irritable.
3. An old paint brush, this is to apply the flux. Don’t use a new or good brush, as over a period of time the bristles will fall out.
4. Various clips and clamps. These help to hold the parts in place whilst soldering, they may also be used as heat sinks to take the heat away from a delicate area. I use the small crocodile type clips, again from Maplins. I have also seen the small spring loaded ladies hair clips being used; these can be obtained from any chemist.
5. Various bits of metal and wood to hold the parts in place while you solder. I find the wooden stirrers from High Street Coffee shops to be great for this. I have found, if you pull them between your finger and thumb a few times to bend them, you have better control whilst holding parts in place.
6. A hard surface to work on, I use a piece of ¾ inch ply wood. The amount of times you see people soldering on a green mat in modelling books is unbelievable.
7. A solder sucker, not essential but handy if you have one. It’s just a spring loaded device, that when heat is applied to a joint and the button pressed it will remove the solder.
8. Last but not least; Soldering Iron complete with stand and sponge (sold separate, cost £10- £17). The sponge should always be kept damp, as this is used for cleaning the tip of the iron.

Soldering Irons

The list of soldering irons on the market is as long as your arm. I always use Weller brand soldering irons, as this was the company which supplied irons to G.E.C. Marconi when I did my apprenticeship with them back in 1972. I always found them to be a very reliable iron. These irons are not that expensive, it depends on the type you want. Mine cost me about £11- £36 depending on the size. (Please note that is today’s price, my irons are about 10 years old)

I have three main irons I use the most:-
1 x 12watt 230volt, for detail work. This is fitted with a copper tip which are replaceable.
1 x 40watt 230volt, for heavy duty work, again fitted with a copper tip,
1x 40watt 230volt fitted with an iron tip for white metal work. This one is very easy to work with as you get little to none corrosion on the tip from the flux. Each time you use it just give it a wipe on the damp sponge and away you go.

The Irons fitted with the copper tips have to be kept in good shape to get the best results. You will find that over a period of time the acid in the flux tends to eat away the end of the tip and scale or scab will form. This is no problem, just redress the tip using a file, and give it a little dab on the sponge, re-tin the end and carry on as normal.

To keep the tip in good shape there is a little procedure I go through every time I use the iron, that is “wipe the tip on the sponge when removing iron from the stand, solder the joint and wipe the tip again before putting it back into the stand� If you follow this simple procedure you will always have a clean iron and the tip will last longer.

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Technique

One of the main reasons you get a poor joint in soldering is due to the fact the parts to be joined are not clean, the brass may look nice and shinny, but it will still have a certain amount of oxides on the surface. For a good solid well bonded joint cleanliness is paramount.

Before I remove the Photo Etched (P.E.) parts from the fret I give them a gentle rub over with the fiber glass pen. I then remove the parts, offer the two together (a dry run if you like). When happy with the fit, I put a small amount of flux in one spot pick up a small amount of solder with the iron, and tack the part in place. When happy every thing is o.k. I run a loaded brush of flux along the joint, pick up a little more solder and run the iron along the joint. The solder will solidify as the iron moves along. At this stage you may notice there is a greasy residue on the brass, by the joint, this is quite normal. It is from the flux evaporating when it comes into contact with the hot iron. It must be cleaned off, as it will eat through any paint surface you put on top of it. To clean it off, just simply put it in a bowl of hot water, and using a cheap toothbrush, give it a gentle scrub with a little washing up liquid or one of the cream cleaner liquids. The latter tends to polish the brass up very nicely. Carr’s also produce a neutralising rinse, which is a very mild alkaline that gets rid of any excess acid left on the work after it has been washed.

At this stage it is time to give the part a good inspection, you may notice the joint may have an uneven surface or there may be too much solder in one area. This is no problem; just give the area a rub with the fiber glass brush or a needle file to remove the excess. If you do use a file you may find the solder will clog up the teeth. To prevent this from happening, rub a little talcum powder onto the file.

For fine work, like hand rails etc, I use the same method as above, but using the 12watt iron and very little solder.

Electrical Solder

Earlier in the article I was telling you about electrical solder. If you pick up a blob of this solder on the iron it will not run along the joint, this is because the flux inside the solder has already evaporated. To solder with this medium you must apply the heat to the surface of the work and introduce the solder. There are two major problems with this, one is you need that much heat you could distort the parts. The other is the resin based flux in the solder doesn’t completely come out, which means after a few months/ years the paint work on your prize wining kit will start to blister. YOU HAVE BEEN WARNED!

Whitemetal

This is an area that a lot of modellers are frightened of, soldering whitemetal. As whitemetal has a melting point of around 150 degrees C you must control the temperature of the iron. There are many ways you can do this, you could buy a temperature controlled iron, quite expensive, or you could build your own controller from a kit, I believe Maplins do one; check out their web site: Maplin. Mine was made for me by a friend in a model railway group. The temperature at which low temp solder melts is around 70 degrees C. Once you have got the temperature set correctly on the iron (practice on some scrap whitemetal) there is no problem.

To start off, give both surfaces of the whitemetal a good clean, I use a small brass wire brush for this; test fit the part, apply Carr’s Red Flux to both surfaces and tin them. To tin them means to apply a little solder to the mating surfaces. Again test fit the parts, if all is o.k. then apply more flux to both surfaces and, with a clean iron, apply heat until the solder flows across the joint. Clean the resulting joint up with the brass brush.

If you wish to join whitemetal to brass, then the brass part should be tinned with 145 degree solder before the joint is made. This helps to make a stronger joint.

Conclusion

In this article I have tried to show how simple it is to solder, when I first started, years ago, I made mistakes and still do but don’t let that worry you, get a bit of scrap brass, get a bit of scrap whitemetal and give it a go. Try using your own methods, as I say these are only my working procedures, yours could be better who knows. All I know is that I get good results from them.

Remember the golden rules:-

Keep your iron clean
Keep your sponge damp
Use the correct flux
Use the correct solder

Warning

Some of the metals used in solder, and the chemicals used in flux can be very harmful. Always wash your hands after handling them. Keep them out of reach of children and clean up any spillages.

Happy soldering!