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Material Choices

This is very much down to the individual... It may be trite to say this, but if it does what you want it to then it is a legitimate choice. Gauge '3' is a strange mixture of modelling and model engineering. It has quite rightly, (in my view), been called the point at which models cease to be scale.

I take the viewpoint that a Gauge '1 loco is a scale model and Gauge '3' loco is a small loco.

The traditional locomotive building materials have been brass, copper, steel and iron. If you are building a live steam locomotive then these are still your only choices due the heat and stresses involved.

Classical designs of locomotive -such as those of Henry Greenly and Lillian Lawrence (LBSC) will use imperial dimensions normally based on some multiple of 1/64th of an inch and specify plate thickness in SWG. Modern designs will specify the sizes either in decimal inches or mm. As a guide when deciding which dimension is the closest to the one required then err on being slightly thicker.

Brass

Brass is a an alloy of copper and zinc. It has several advantages for building. It is reasonably easy to cut, has a great affinity for lead and tin based solder and can be rolled and folded very simply. However some alloys contain other metals to increase corrosion resistance (aluminium) or to increase the cutting rate (lead). Brass should never be used for water plumbing but the use in steam plumbing is acceptable.

Iron

Iron is fairly hard to obtain nowadays and is normally found in the shape of castings for wheels and steam cylinders. Pure iron will not rust. The casting will leave a crust of iron and sand that will have to be cut through with T/C tipped tools to reach under the crust. Thereafter the soft iron may be cut with HSS tools.

Steel

Mild Steel is normally the one that you will use. This is strong, cuts well -but rusts easily. It is easy to silver solder and braze. Stick welding is normally done on pieces greater than 3mm thick. Locomotive frames are quite strong enough at 2mm thickness. Most suppliers will cut your pieces roughly to size with guillotine or power saw. You may then chain drill the shapes from it.

Stainless steel is quite a different animal. This is very strong, rust proof and very hard to cut. The most common alloy you will find is either 304 or 316, both of which are commercial grade S/S and exist in sheet, tube and angle. They are very hard to join (in a domestic environment) and normally only brazing and silver soldering is used.

Copper

Copper is getting very expensive -but it is still the boilermaker’s choice of metal. The boilers of HG and LBSC reflect a design pedigree that is empirical and tested. The designs of Evans and Noble are more modern and calculated in their design. Copper can be joined by TIG, brazing, silver soldering and rivets. How you join the copper sheet together depends on how thick it is. Do not attempt to "tap" threads in copper as this is unbelievably difficult. The copper sticks to the tap and you can end up with a tap firmly stuck into the copper. Rather, bore a hole and solder in a bronze plug and tap that. It is possible to cut a thread on copper rod and use this to bolt up as in boiler stays, but phosphor bronze is a better bet as it is far more rugged.

If you are building a steam outline loco or a diesel or electric loco then other materials can be used. Primary amongst these will be aluminium, plastic sheeting and plywood.

Aluminium

There are several problems using aluminium. The oxide layer on the surface makes fusion jointing a specialised process and most of the joints will be mechanical (screws and rivets). The metal is very light and strong but suffers from work hardening producing brittle cracks. It machines like a dream but care must be taken that the razor-like tinsel swarf does not fly into the face.

Plastic Sheet

Slaters "Plastikard" is probably the one that most people are familiar with. However there are a whole family of plastics that are suitable for model work.

PolyCarbonate. This is a clear plastic that is amazingly strong, but care must be taken when cutting it as the melting point is only 80C and the cutting tool can become trapped in it.

ABS. This is good strong flexible plastic that responds well to the "crack and snap" method of cutting. Available in several thicknesses, do not attempt "crack and snap" at over 60thou.

HIPS. This is a very hard rigid plastic that is best suited to large flat expanses, but will bend at very thin sections. Does not respond well to "crack and snap" but will have to be sawn or knifed.

Joining them is normally down to glues, either solvent weld (MEK), Cyano (superglue), and Epoxy.

Plywood

Plywood is nice to work with. It is strong, cuts easily and does not distort badly. However it does have problems of its own. There are numerous types of ply, most of the sort that will be used is normally referred to as "modellers ply". This is normally of three layers thickness and can be fret sawed or cut with a knife to the required shape. Three ply will bend preferentially one way, so forward planning is needed before cutting. Normal ply has the layers of the grain at 90 degrees for strength, however boat building ply has the layers at 60 degrees to increase the flexibility of the ply to follow curves.

Fillers

These are used to conceal the joint gaps and produce a smooth seamless surface. In the case of the classical metals the only possible filler -is lead. This used to be used in automotive repairs but the "art of the lead sled" is almost extinct, as is the plumbers ability to "wipe a joint". Both techniques involve the melting of the lead to the point of plasticity at which point an impact will liquifiy the lead and allow the user to wipe with a spatula or use a sled paddle to slap the lead to shape. The metal being "leaded" may require some highly corrosive fluxes that will need to be washed off. The lead will also cause the file to clog -use a wire brush on the grooves frequently.

Modern fillers are based on plastics. These can either be of the 50/50 type in which the hardener and the base are putties mixed together and squished into the joint. The prime example of this type would be Milliput. Other fillers have a separate hardener and base which you mix in the ratio of a pea to a golf ball sizes. There are two main types here -one uses glass fibre strands and the other talcum powder as the bulking agent. Isopon P40 is an example of the glass fibre type and Isopon P38 an example of the talcum powder type. Other wood fillers used for shallow depths are air-drying.

P40 has the advantage that it is very sticky and can be used to structurally strengthen a joint as well as filling the gap. P38 although initially sticky cannot be used in this manner -it only fills gaps.

Fine surface filling is normally done with "stopping compound" this is a plastic clay mixed with a solvent that is applied in very thin layers and dries to a hard finish. An example of this would be "Squadron Putty" which is made in the USA but do not be alarmed at the warning notices on the tube, they are required by US law...


Addendum.

These are sheets that may help you.

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Page last modified on February 25, 2018, at 08:19 PM