Building O Gauge Online

A recurring theme in e-mails I receive from people who have viewed this website and who are constructing various locomotives is the subject of soldering. There is no mystery and soldering is not some dark art practiced only by the select few. The old adage practise makes perfect is in this case true. This along with knowing a few ground rules and having a little confidence, is all that is required.

In this article we will look at soldering irons, solder, fluxes and some of the extra tools that come in handy from time to time, finishing with some pictures of various items soldered to one another.

Basic Rules and Hints & Tips

Cleanliness is absolutely essential. Solder will not take onto surfaces that are dirty, greasy or oxidised.

Always have a damp sponge in a small glass pot available to wipe excess solder and debris from the tip of the iron.

If the iron or the tip is new the tip will need tinning which I do using standard electrical 60/40 solder which contains a core of rosin flux. Bring the iron up to operating temperature, then on a burn proof surface like an old ceramic tile, rest the tip on the surface and apply a generous amount of solder to form a molten ball of solder around the tip. Wipe the tip on a damp sponge which will leave a very thin film of solder covering the tip, this is tinning. You will find it necessary to repeat this operation from time to time mainly because the solder we use in modelling does not contain any flux and the surface of the tip will become oxidised.

Under no circumstances ever file or sand the tip of a modern soldering iron. Virtually all soldering iron tips that you will come across have a coating on them. This coating does eventually wear out and the tip will begin to disintegrate, usually noticeable by there being a hard rough patch somewhere on the tip that will not retain solder. Replace them at this point before the lack of heat dissipation has a chance to damage the heating element.

What is solder? Standard solder is a mixture of lead and tin, small amounts of antimony, bismuth, cadmium or silver are added which alters the melting point. There is currently much concern about the use of lead in solder and its effects on the environment. Lead free solders have been around for a while and are becoming much more prevalent.

The lower the melting point of the solder the less mechanical strength the resulting joint will have. The 70°C solder that we use in modelling is particularly brittle and really only suited to attaching fine whitemetal details where no mechanical strength is required. For larger whitemetal items such as bogie frames where mechanical strength is required, 145°C solder is mechanically much stronger but care needs to be taken when assembling the parts, due to the higher temperatures involved.

Try to have the parts to be soldered secured in some way other than holding them in your fingers. Two reasons for this, brass is a very good conductor of heat and will get very hot even at an appreciable distance from the joint being made and if the objects moves while the solder is solidifying, the joint will be weak.

Flux is the all important key to good soldering. What the flux does is it draws the solder from the tip of the iron and onto/into the joint while at the same time removing any oxidisation from the surface. It is the removal of the oxidisation that is the key to getting the solder to fuse onto the surface properly.

Since this piece was written we have moved away from using the acid based fluxes that modellers traditionally use. These acid based fluxes present modellers with several problems. They are highly corrosive and will start to rust steel wheels almost before your very eyes. Many people find the fumes given off during soldering irritates their eyes and nasal passages. Nickel silver starts to corrode quite quickly under their influence. Flux residue on fingers leaves stains on brass that are very difficult to remove. Everything HAS to be washed down at the end of every modelling session sometimes with chemicals that are less than desirable. It is my opinion that these fluxes are totally unsuitable for fine scale modelling and the only reason they are used and are still in use is because they always have been and no one has come up with an alternative. NOT anymore - In our Webshop you will find our own Water Based Safety Flux. This product works on brass, nickel silver whitemetal, phosphor bronze and some types of steel. It is very mild, low fume and adresses all of the problems listed above. While clean up at the end of a modelling session is a good habit to get into, with our flux this can be done with nothing more than warm running water and cheap washing up liquid. Your model will stay cleaner throughout the build which means less clean up at the end prior to painting.

A little too much flux is probably better than not enough and if you wash the area down in warm soapy water as soon as you have finished construction then things should be OK. Pay extra attention to areas of nickel silver, especially fine grilles because the corrosive nature of acid based flux turns it green, if you are using our flux this is not a problem . I use cheap children’s paintbrushes to apply flux, there is no point spending money on brushes for this use because the acid based fluxes corrode the metal that holds the bristles to the handle and they fall apart eventually, again not a problem if you are using our flux.

For those of you that are terrified by whitemetal soldering, obtain some cheap, very thick plumbers solder, cut it into lengths and twist each piece over on itself 2 or 3 times so that it is twice or three times as thick as it was. Now, using flux and 70°C solder, practice soldering the pieces to each other in various shapes. If you can do this, then you can solder even very tiny pieces of whitemetal. Practice makes perfect but confidence also helps. Try the same exercise with 145°C solder, it can be done!

Soldering whitemetal to brass is awkward but by no means impossible. The problem is that 70°C solder does not fuse onto the surface of brass very well. The answer is to put a very thin film of 145°C solder onto the brass where you wish to make the joint and then solder the two pieces together using 70°C solder. The 145°C solder is much closer in its properties to whitemetal than the brass is, so it’s almost like joining two pieces of whitemetal except you are not too bothered if the one side melts.

A glass fibre pen is an invaluable tool. Used for cleaning an area prior to fluxing and soldering it is much easier to use than sandpaper. For cleaning around a joint after it has been made it will remove a thin film of solder in a few strokes leaving you with a very clean and professional looking joint. Beware the glass fibre splinters that these pens leave behind though. They are extremely sharp and will pierce skin quite easily.

Reversible (squeeze to let go) tweezers are another useful tool but be careful holding whitemetal objects with them as they are usually strong enough to deform the object if it gets close to its melting point.

Miniature wooden clothes pegs, sold in craft shops for holding cards to string are another useful item for holding parts in position.

If you really must hold the parts while you solder them, and there are times when you have to, put something between your fingers and the object that does not transmit heat very well, like half a wooden clothes peg.

Holding parts in position becomes more important if the area is going to get very hot. The effect is more noticeable with nickel silver but does happen with very thin brass, when a lot of heat is applied the thermal shock will make the metal start to curl. This is one of the reasons why I don’t like solder creams, their melting point is usually above 170°C and you will have to get the entire area well above this temperature for the solder to become fully molten which risks deforming the metal.

Put a little thought into construction and use the properties of the solder’s melting point to your advantage. For example, the roof sections of a diesel locomotive. Solder the main roof sections to their roof formers with the highest melting point solder you can get away with. Then, when you come to apply details and overlay bits, if you use 145°C solder there is little risk of the other parts springing apart because they will not become hot enough to melt the solder joints.

There is nothing wrong with using standard 60/40 electrical solder which contains a rosin flux in its core to form joints that need to be particularly strong but you will still need to use liquid flux.

On very long or complicated joints, especially those where two pieces of brass sheet are butt jointed to each other, it may not be possible to make the joint in one continuous run. To get around this problem, tack solder the items along the joint at several points, then fill in between the first and second tack, then the third and fourth tack etc, returning to the space between the second and third tack etc once the solder either side has cooled.

Where an item has a half etched line along which the item is folded, painting a little flux into the gap and soldering along the line once the item is folded will give the fold strength.


Soldering Irons

Soldering irons are very personal items, other people’s often don’t feel quite the same as your own. Out of the three that I currently own, I often find myself using just one for almost all jobs, simply because I have had hundreds of hours use out of it and I know what it will and won’t do in a given situation. I suppose you could sum this up by saying that it is a combination of practice, confidence and pure laziness. There are times, though, when the right tool for the job is an absolute must, hence the three soldering irons that I shall describe here.

A word about wattage before we continue. The wattage of an iron has absolutely no bearing whatsoever on how hot it gets. What it does mean, is how much power the iron has in reserve to keep the tip at the operating temperature when the item being soldered is drawing heat from the tip and therefore cooling it down.

	Soldering Iron 1 This is the one I use the most, a professional Weller 24 Volt 50 Watt soldering station. Tip temperature is dependent on the tip that is fitted and is controlled by a magnetic cut out built into the shaft which contains the heating element. The tip that I use is a PTAA8 which gives a temperature of 430°C/800°F. The biggest problem with these irons is someone changing the tip and tightening down the shaft that retains it so far, that it is unable to move in and out. The tip must be able to do this for the temperature control system to operate correctly. Failure to observe this will result in the tip melting, closely followed by the heating element expiring. I use this iron on 95% of brass and nickel silver work and some larger whitemetal items, usually with either 145°C solder or standard 60/40 electrical solder which melts at around 186°C, although I have used it with 70°C solder.
	Soldering Iron 2 This is a standard 240V 25W Antex iron but it is wired through a lamp dimmer switch built into a plug top case. Favourite temperature settings are achieved by trial and error and then marked on the case in pencil or permanent marker. I use this iron exclusively for small whitemetal items with 70°C solder.
	Soldering Iron 3 This is a monster but very useful for long seams on brass bodies. It is a 240V 75W Weller iron and it will provide and maintain a substantial amount of heat on the item being soldered.

A few bits and pieces soldered together

	This is a piece of brass  40mm x 20mm x 0.3mm simply joined to another piece of brass at a 90 degree angle. All I have done here is cleaned the item then held it in position and run a line of liquid flux along the edge on this side only. Then with a small amount of 145° solder on the tip of the iron, run the tip slowly along the join.
	This is the opposite side of the piece after soldering. If you look carefully at this picture and the next one in the sequence you may be able to see that there is a very thin line of solder visible at the point where the two pieces meet. The liquid flux although only applied to the other side is so thin that a small amount will have seeped under the joint and it has drawn a little of the solder through.
	If the piece needed to be mechanically strong then I would run another solder joint down this side, otherwise this side can simply be cleaned up. If this were some item that was on the outside of a locomotive we would have a nice tidy joint showing on the outside with the less tidy and mechanical aspect of the joint on the inside where it is less likely to be seen.
	Here we see the side I made the joint on after a quick cleanup with a glass fibre pen. What you should be able to see is that there is a very thin skin of solder about 2 or 3mm wide on both pieces of brass with a main fillet running along the junction of the two pieces.
	Here we are sandwiching two pieces of brass together which is a widely used technique in locomotive construction to provide relief where etched detail would not be enough. The underside and edges of the smaller piece were cleaned and flux applied to both surfaces. Next I have run around the edge with the tip of the iron loaded with a small amount of solder, reloading it as necessary.
	As you can see from this cleanup shot the solder deposited around the edge was only a very thin skin. A few wipes with a glass fibre pen has removed most of it, the important thing is that the flux has done its job and sucked a very small amount of solder under the edge. This is all that is needed, the piece is not going to fall off and in fact would be very difficult to remove without destroying it.
	The same piece but this time we are bonding a piece of nickel silver in the centre of the piece of brass bonded in the last sequence of photo’s. The same principle is used, if anything I have been a bit heavy handed with the solder but it is only a thin skin so it is easily removed.
	After a bit of a cleanup. As before the solder has been sucked under the edge by the flux but not so far under so as to reach the middle because you can still see the brass through the hole in the middle of the nickel silver piece.
	Where the kit maker has provided  a half etched line in an item it usually (but not always) means you fold the item along the line with the half etched part on the inside.
	Here we see the item folded. Make sure the item is completely clean before folding and paint a very thin line of flux along the fold.
	Run a very small amount of solder along the fold. The liquid flux will draw the solder right into the small void where the half etched line forms the corner. The result will be a very strong fold that will not flex.
	The second edge folded up and soldered in the same way as the first. On very small pieces it may be impossible to get into the joint with a glass fibre pen which is not too important because the joint is internal and will likely not be seen. What is important is that the item is given a good wash down in warm soapy water to remove any flux that has not boiled off in the soldering process.
	Top edge folded over and in this case a very small amount of solder applied along the edge from the outside in a very similar way to the piece of brass soldered in the first photograph. If I could have got the soldering iron tip inside along the entire length then I would have done so.
	The same edge after a bit of careful cleanup with a glass fibre pen and some fine wet and dry paper. If the two edges meet perfectly you should be able to remove all traces of solder from the outside to the point where it is very difficult to even see the join.
	Here I have applied a small smear of 145° solder to the brass sheet ready to bond a small whitemetal item to it.
	The whitemetal item is then soldered using the low temperature iron and 70° solder. The flux should draw the 70° solder under the piece and bond it to the surface
	The reverse principle to the piece above, a small piece of brass added to a whitmetal item with my fingers to give an idea of size. I gave the small piece of brass a thin film of 145° solder on its reverse side. It was then bonded by running the tip of the low temperature iron around the edge with the tip loaded with a tiny amount of 70° solder and letting the flux draw it under the piece.