Broad Gauge Mail Coach - part 2
My previous post in this series ended on a 'cliff-hanger' – how was I to escape from the 'hinge' problem?
After a little thought, the solution proved very simple. I used my jewellers' snips to cut a 1mm strip from the edge of some brass sheet and then folded the strip to make three staples, which pressed into the slots on the adjacent compartment doors. It was fortunate that the doors were hung 'back to back' so that the staples could be kept quite short.
I did discover a small problem later, when fitting the partition between the compartments, since I had to file slots in the partition to clear these 'staples'. I could, of course, have used individual L-shaped strips but they would have been more fiddly to fix in place. I did, however, have to use this method for the single door at the other end of one side.
It sometimes puzzles me how kit designers decide which details to include in their models. Why do these etches have slots for these almost invisible hinges but no provision for door handles or grab rails?
Anyway – on with the build:
The next step was to fit the two partitions. These have vestigial tabs, to register with slots in the floor. I 'tacked' both these partitions in position, with small blobs of solder, while I checked that the coach sides fitted snugly against the partitions and the floor. It is important to fit the taller partition the correct way round, so that the etched detail shows above the low section of the roof (I almost missed this!). As I mentioned above, I had to file slots in one of the partitions and also needed to trim the other a little, to ensure the sides would fit flush against the floor. Once I was satisfied with the 'fit', I ran solder along the partition seams and, similarly, soldered the sides to the edges of the floor.
I always apply a fairly generous dose of phosphoric acid flux along the seams and then run 60/40 solder along the joint with a sweep of the iron. It is important to remember that the only role of the iron is to apply heat. It should never be pressed hard against the work and certainly not used to press joints together. If pressure is needed, use something non-conducting, such as wood, to avoid taking heat away. I often use fingers, at what I hope is a safe distance, but brass is a good conductor and the temperature rises very rapidly, even several centimetres away! It is important to wash the completed assembly thoroughly with water, to remove any residual acid which will otherwise continue to attack the metal. It's a good idea to dip any burnt fingers in cold water, too 
That's almost it, for the main body, but the the sting in the tail arrives with the ends! The sides have a 'tumble-home' but the supplied ends are straight. The instructions state “The top of the sides now need to be bent inwards so that the ends are vertical. The ends fit between the sides ….. The lower half of the sides now need to be curved in to meet the ends” The point seems to be that the front corners of the prototype are curved, as in many early GWR coaches.
Making a rounded end may be possible in 7mm scale but I could not see how to achieve it at the smaller scale, without courting disaster. I decided to fit the upper part of the sides flat against the edges of the ends and then curve the 'tumble-home' to meet the end. Trying to get a smooth double curvature was not at all easy. I intend to try rounding the corners by using a file, later, possibly with a wire fillet along the inside of the vertical joint.
The two roofs have a very slight curvature. I used a steel tube as a rolling pin, to make the curve, with the roof laid on a mouse mat, to provide a soft surface. In fact, the curvature is so slight that I over-did it the first time.
Particularly interesting features of the prototypes were the skylights on the roof, which were presumably a Post Office requirement. When I looked at these items on the fret, I was a little apprehensive but they actually work very well.
The important thing to note is that the fold for the triangular sections is part way down the main sides. It is very easy to inadvertently bend the fragile glazing bars, if these are not clamped firmly in a vice, while making this initial fold to an angle of around 60°. I have taken a photo through my illuminated magnifier to show how I did this, by using some aluminium-angle, clamped in the vice together with the fret, to define the fold line. In 4mm scale, these parts are quite small.
After making this first fold, the brass strip then has to be folded to make a box shape, with two tabs at the sides, which secure the completed assemblies to the roof, from below. I found that the completed skylights were a good close fit in the cut-outs that are provided within the upper roof. I got better at making these skylights, as I worked through the set, but photographs are always cruel and I can see that some straightening of the glazing bars is still needed.
That essentially completes the body of the coach apart from some cast fittings, including oil lamps and ventilators. I may try the technique described by Dave John , to hold down the roofs with magnets.
The next task will be to build the chassis, which looks reasonably straight-forward, although I need to think about the type of break gear that would have been in use in 1868. I think the overall effect, so far, is quite pleasing:
Mike
Edited by MikeOxon
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