Soldering To Be Proud Of: (I learned so much from the video) Learn how with this essential guide - Model Railway Engineer

Soldering To Be Proud Of: (I learned so much from the video) Learn how with this essential guide

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model railway solderingWant to improve your track wiring and electrics? Soldering is the only way but what’s the best solder to use? What should you look for in a soldering iron? How can get the best solder joints? Here’s the MRE definitive guide to soldering.

The majority of the problems I come across on my layouts, and those of visitors to this blog, are down to track connects and poor electrical contacts in wiring. Without a good connection the electricity won’t flow and the trains and accessories won’t function correctly.

This is where soldering comes in.

Why Solder?

While other techniques of joining or fixing wires – twisting them together or using a terminal block for example – may seem easier they are prone to problems. Wires fray and work lose, bare metal oxidises and twisted strands may not make a complete connection.

Soldering, by contrast, can initially seem like a lot of work but once learnt is actually the easiest way of making reliable joints between electrical contacts – dropper wires to rails etc – and is infinitely better at passing electricity than any other option.

Soldering creates a conducting bond between the two metals being worked on and there’s no opportunity for the wires to fray or break.
Other reasons to solder include:

  • Because it creates a strong, long lasting, join
  • Because mistakes and errors can be easily corrected,
  • Because solder joints are robust – rarely work lose with vibration of trains running over rails for example.
  • Because it improves connection between the metals allowing electricity to flow better

We’ll come to how to solder in a minute but first make sure you’ve got the best equipment.

What to look for in a soldering iron, solder and accessories

Soldering Iron

It’s a simple fact that being able to deliver the right amount of heat at the right place as quickly as possible is one of the fundamentals needed of good soldering irons.

Equally, being able to apply heat precisely so as not to damage nearby plastics – track sleepers being a case in point – is another key requirement.

Finally, the iron core should pass the heat from the heating unit to the tip consistently and quickly. A lot of cheap irons fail here, with the heat distributed unequally and taking a long time to heat the tip to the required temperature.

These features form the basics of all good irons. You certainly don’t want to use the old clunky types probably lying around in your sheds or garage.

It took me a while to find a soldering iron that provided these but my preferred choice – and a choice echo’d on some of the model railway forums – is the Antex range. I use the Antex XS25 iron, with a variety of tips from .5 to 1.5mil, for quick jobs but switch to this 48W temperature controlled iron for track work and when I have a lot of soldering to do. The more powerful unit is needed for tracks as rails act as heat sinks and drain heat from smaller irons faster than they can reheat.

A word of warning, there are a lot of cheaper so called temperature controlled irons aren’t really temperature controlled but adjust the voltage being supplied and can be slow and problematic. It took a while to find the one mentioned above that offers decent control without costing a fortune. As yet, I’ve not had a problem with it.

The best solder

Having the best solder is just as important as having the right iron. While solders may look the same the metals used and the ratio of their mix make a huge difference to the temperature needed to melt it, how easy it is to work with, the hardness and the quality of the joint it creates.

In fact, many of the problems with soldering can be traced to using the wrong solder.

So what’s the best solder?

The answer lies in the chemistry and physics but and without diving into to much detail it’s down how the metals involved react to heat. At it heats up and change from solid to molten and then back as it cools solder passes through an interim ‘plastic’ stage. While in this state it doesn’t flow easily – making it harder to get it where you want it, wires can come free and the surface can be disturbed resulting in rough, ugly, looking joints.

The best solder then is one that has a mix of metals giving a low melting point – so avoiding the plastic state while it heats up fully – yet one one that’s still hard when set.

I’ve found a mix of 63% Tin to 37% Lead to be the best. Other mixes, such as 50/50 and Tin/Lead-free, have higher melting points (e.g. they take longer to reach full melt point) and take longer to cool.

The 63/37 mix however melts very fast – and at low 183C – and returns to its solid form just as quickly. You don’t burn your fingers – or sleepers – while holding the iron in place waiting for the solder to melt and you can release the wires quickly afterwards without worrying that they will come free because the solder hasn’t completely solidified.

I also look for a solder with a Rosin/flux-core.

The flux cleans the surface of the material being worked on to give a better joint and solder with this built-in saves having to wield the solder, iron and separate flux at the same time. (Rosin is a form of flux).

After searching, I’ve found this solder to be offer the best results. It’s small diameter makes it ideal for precise work and the Tin/Lead 63/37 mix is spot on for low temperature, rapid melting / cooling.

There’s a very good description of solder in this video. It’s a classic old school presentation but does a great job of explaining what solder is and how it works.

The interesting bit is from time point 2:20 to 9.56

Must have accessories
Cleaning Pencil:
An often overlooked but in my view vital accessories for high quality soldering is a cleaning pencil. While the flux in the solder cleans the surfaces being worked on and helps the molten solder bind, cleaning the surfaces with an abrasive cleaner will remove more dirt and oxidisation preventing a good bond and so give a much, much, better joint. This is particularly the case with rails which attract lots of dirt and grime.

Fibreglass abrasive brushes work a treat for this (they make a good general rail cleaner too) but they do wear out quickly however so I use this one which has replaceable heads.

Oh how my fingers would have appreciated me knowing about this when I first started.

Metal being soldered conducts not just electricity but heat and if you’ve ever tried holding a rail or wire while soldering it you’ll know the heat moves quickly and it isn’t too long before you need to let go. Invariably, this is just after the perfect joint has been made and as you let go the wires move before the solder has hardened wrecking the whole thing.

It was after one particularly painful finger burning experience that I started looking around for an alternative method of holding wires together and discovered the joys of crocodile clips and clamps.

The Am-Tech helping hands has been my fingers-friend ever since. It features not just clamps on adjustable arms but also a magnifying glass and soldering iron holder and is never far from reach when I’m working on my layout electrics.

A set of all metal pliers is also usually close to hand. Attaching these to wires after the the point of soldering but before the signal or point motor acts as a heat sink, keeping the heat away from the delicate electronics that might otherwise be damaged. These can be found in any tool or DIY store.

Wire Wool:
Oxidisation builds up on soldering iron tips very rapidly and if not removed with frequently cleaning will contaminate the solder reducing the quality of the joint. Wire wool, or even a damp sponge, should be used to clean your soldering iron frequently.

How To Solder

For the impatient, watch this quick video:

There are lots of guides to soldering across the web, but this one from Instructables is one of my favourites. As it covers not just soldering but also cleaning.

“If you have a decent iron, the right solder and a cleaning scour you are halfway there now you just need to pay attention to a couple of important points and you will get good solder joints.

Modern soldering iron tips tend to have special coatings, this is good because it prevents the oxidising as quickly as they used to. This coating is the reason I say you should never file or sand your tip to clean it, once you start that down that route, you will probably have to keep doing it every so often and the tip will be worn out quite quickly. If you look after the tip, it will last a long time.

Now this oxidisation happens quickly when the tip is hot, you can see it because the tip goes from shiny silver to dark and dull, it actually goes quite grey in colour and can almost become black. Now the problem is this layer of oxidation reduces heat transfer. Some people don’t realise just what an effect this has and keep trying to solder with the iron in that state. The problem is, you will struggle to make a single solder joint with a tip like that.

The secret is to clean it before every joint. Well sometimes you can do a few joints straight after each other and I would usually at least do both wires of a resistor for instance, but you can’t just keep soldering without cleaning the tip.

Now cleaning can just mean wiping the tip on your scouring pad a couple of times, so no big deal. But if the irons been sitting for a few minutes you need to go a bit further. You need to clean and then ‘tin’ the tip.

The ‘tinning’ prevents the oxidation of the tip and to do it the tip needs to be hot and clean. So you pick up your hot iron, wipe the tip on the scouring pad a few times and then immediately melt solder onto the tip to tin it. Don’t be shy with the solder, it’s cheap and it will drop of the tip as you do it, but some will stick, kind of ‘paint’ the tip with solder and then wipe the excess on your scour, then do your solder joints straight away.

If you put the iron down for a minute after tinning it, you will probably just need to wipe it on the scouring pad again and then you can solder. But wait too long and you will need to clean and tin it again. This is why it’s a good idea to load a board up with say all the resistors and then solder them all in at once instead of putting one in, solder it, put the next one in etc. That way you can do a few joints, wipe clean and do a few more etc. By the way, you should tin a new tip the first time you use it, before the iron gets hot for the first time the tip will be shiny, it heats up and starts going dark, clean it and tin it.

It’s not really that difficult and with practice it will become second nature, you will get to know when you need to tin the tip and when you can get away with just wiping it. Be careful though wiping it enough will always clean it, but it should be shiny after wiping it, or it will oxidise very quickly.

Now the idea with soldering is you want to get both of the things you are joining hot enough and then introduce solder. Don’t load up the tip with solder and try to transfer it to the joint. You should touch both pieces you want to join with the tip at the same time and hold it there for a couple of seconds to allow them to heat up.

Now the best way to work out what you should be heating is to remember a simple rule: Solder will always flow towards heat.

So hold your iron on the join for a second or two, then introduce solder into the join, it will melt when it touches the iron, as soon as you see the solder flow into the joint, lift the soldering iron away. Don’t jerk it away, just lift it off.

Now to do this well you need to have everything secured in place so you can hold the iron in one hand and the solder in the other. No balancing tricks (until you know what your doing and can get away with it). This requires having everything held in place by its own weight or under tension or with a clamp, or whatever, no chasing parts around the bench with a hot iron. ”

What Next

Products To Help:

Learn More: 

  • Great Q&A guide to common soldering problems from gurus at Adafruit
  • In-depth explanation of solder composition and issues around lead-free solder
  • Railway Electrics: Comprehensive guide to all model railway electrics

And that’s it! All I can say and recommend now is go and practice, practice, practice but if you’ve followed these tips you shouldn’t struggle with soldering any more.

Let me know how you get on.

PS, If you liked these tips, you might enjoy my newsletter, Footplate. Over 20,000 model railway fans get my tips direct to their inbox with this. It's completely free, you can unsubscribe at any time and I promise to never spam you. Sign up now.

  1. Luka Paunović - January 1, 2017

    An amazing article for beginners.
    I am not novice to electronics but this article is useful for newbee’s.

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