Sometimes a daunting subject or task but can it be carried out by the less initiated and especially when fine soldering is required when modelling? The simple answer is ‘yes‘. The following is based upon a Hornby Forum post by Chrissaf and my thanks to him for allowing myself to publish it here.

In Chrissaf‘s opinion anyone who wants to get the best possible outcome from the model railway hobby does need to aspire to being proficient in basic electrical soldering. That is quite true and is the reason this article is included here.

It is often said by folk that they cannot solder or that they tried and made a mess of it. With regard the first part of that statement, anybody can learn to solder and it really isn‘t difficult and with regard to the second, you must have the right tools for the job. It is quite easy to make a ‘dogs dinner‘ of it and especially if anyone was trying to use a 30 watt soldering iron with a ‘10mm wide‘ soldering bit to solder a 0.5mm wire on a DCC decoder pad.

In order to be able to at least make a very good start in this field this guide will take you along a path where a good understanding will see you soldering with confidence. A one time caveat is that you should always be aware you are dealing with very hot equipment so do be careful out there. Whilst this is not a comprehensive guide to soldering neither Chrissaf nor myself can be held responsible for anyone making errors as a result of not following this particular guide correctly.

As with most things it is all about having the right tool for the job in hand. The tools shown below form the basic soldering toolbox needed for delicate electrical work on things like loco wiring repairs and decoder fitting (where DCC sockets don‘t exist). It is also suitable for attaching droppers to track-work and any general need to solder wires together.

The equipment referred to is Chrissaf‘s own recommendation but after years of experience he offers here a very good guide.

Obviously the first thing you need is a soldering iron and the market leaders are Antex and Weller. Do not buy cheap. Cheap irons are more likely to have steel soldering bits as opposed to soft iron or copper. The mistake most soldering newbies make is to use a soldering iron that is too hot and/or too big. For model railways a 15 watt iron is more than adequate. Do avoid the trigger gun (instant heat) type soldering iron as their tips are just not small enough for printed circuit board (PCB) work. Antex produce a wide range of bits for their irons and for track-work and general wire joining, a 2 or 3mm chisel bit is ideal. For wiring on decoders, a bit that is less than 2mm diameter (nearer 1mm) would be preferred.

The above is an example of an Antex 15 watt C15 soldering iron.

One can go overboard and invest in more expensive soldering irons that are digitally temperature controlled etc. but the much cheaper iron above is more than adequate and easy to use by a novice for most model railway related soldering tasks.

Even if you ignore the advice above and buy a cheap iron, if you do nothing else, do not buy cheap ‘lead free‘ solder. Cheap lead free solder requires a much higher temperature to melt and does not flow as easily as the more expensive ‘lead based‘ solder which is so much easier to work with. Novices will really struggle to learn using lead free solder.

The ideal for model railway soldering is 60/40 multi-core of 1.2mm diameter or less. For this type of work solder with a diameter larger than 1.2mm is probably too thick. Multi-core means that it contains flux in little tubes that run the length of the solder and this is an important ingredient needed to make solder flow over the joint when molten. When soldering something that does not solder easily, then additional flux may be needed to supplement the flux in the multi-core. The 60/40 is the % ratio of tin vs lead in the solder.

Materials that will solder very easily are:

1. Copper

2. Brass

3. Nickel Silver (modern track rails)

4. Tin or items coated in tin (tinned)

The key to successful soldering is cleanliness. The two items being soldered together must be free of tarnish (oxidation) and any other foreign matter. The shinier they are, the easier it will be to solder them together. Fine ‘wet n dry‘, a small wire brush or glass fibre pen can clean things, but one easy, less labour intensive, way of preparing the surfaces to be soldered is to ‘tin‘ them first. This, of course, still requires the surfaces to be clean enough to accept the solder.

Tinning involves baring the wire to be soldered and freshly bared wire, i.e insulation removed, should already be clean and shiny enough for tinning. However, if the wire looks dark or greyed then it has probably been subjected to heat and become heavily tarnished (oxidised). The oxidisation needs to be removed before tinning will be successful. Drawing the wire through a folded piece of fine ‘wet n dry‘ or rubbing with wire wool will clean it up. Once clean and shiny, allow contact of the iron and solder to the wire at the same time and the flux in the Multi-core should make the solder flow over the wire. You may need to have both hands free to achieve this so a very small clamp may come in handy. Speed is of the essence, if the insulation starts to creep back up the wire then you are holding the iron against the wire for too long.

Most manufactured solder pads on PCB‘s are tinned at the factory, but even if already tinned, then it is still advisable to use the iron and the solder to add a little more solder to the pad. The reason why will become evident shortly. If the solder pad is not factory tinned and is still the colour of copper, then use a glass fibre cleaning pen to make the copper shiny before applying the solder and iron to tin it.

It is not just the two items being soldered together that need to be clean and tinned. The soldering iron bit tip needs to be clean, shiny and freshly tinned too. The constant heat in the iron will burn any flux residue on the tip and turn it black. The black burned residue must be removed before you use the iron to perform the soldering task. Some use the cheaper option of a damp (not wet) iron cleaning sponge. This does work well, but it is much more preferable to use the more efficient and quicker method of stabbing the iron tip into a pot of brass wool. You need to get into the habit of every time you pick up the soldering iron that you stab (plunge) the iron bit into the brass wool pot 2 or 3 times to clean off the black burnt flux.