A piece of 3 mm copper is cut into a circle. A surplus of about 10 mm is added to the final diameter. This will be the edge (or rim).
Heating up does not take much time, but several heatings are necessary because the material will be compressed quite a lot. The 3 mm thickness increases to almost 3.5 mm on the edge.
To have a close fit to the boiler barrel, the edge is shimmed off to the final diameter.
Support in the lathe is the steel former on which it was hammered and a wooden block to firmly hold it pressed on the former. Light cuts were taken.
An impression of size.
The throat plate takes up a lot of more work and time. First, a piece of copper is flanged, the same way as the boiler back head plate.
Then a second former plate is needed, made of a piece of scrap aluminum, for the outer rim.
A circle is marked out.........
..... and cut by hacksaw and file.
Positioning it on the former, where care should be taken to center it on the former and put it on the correct height.
After clamping it in the vice, the first hammering session brings it into shape. Here the material is stretched, instead of compressed.
There fore several annealing operations are necessary.
The final forming operation (all done by hammering).
The rim (12 mm wide) is marked out and filed to height.
The edges are still 3mm thick and will of course not fit in the small gap between boiler shell and wrapper.
First, the overall height is marked out and cut to size.
An angle grinder is used for trimming down the thickness of these edges. They will start at the original thickness of 3 mm and be ground down to approx 0.5 mm. This way they will fit as close as possible in the wedge-shaped gap between the boiler barrel and outer wrapper.
By test fitting, it becomes clear where to remove excess material.
After a few fittings and grinding operations, the throat plate slides in the gap.
A few final light taps with the hammer, ensures a close fit to the boiler.
The wrapper is now cut to length.
Holding it in the vice, with the aid of the forming block, makes it possible to file it to the correct length and square to the sides.
Once this was done, the throat plate itself was marked off and cut to size.
The final operation is the cutting of the edge.
Roughly done with the angle grinder, and finished with a file.
Almost there. The round corners of the outer wrapper can be made a bit shorter (closer to the rim of the throat plate).
Seen from the inside: a nice fit of both.
Wrapper, boiler shell and throat plate in position.
With an overall length of 441 mm, it is indeed for a 5-inch gauge locomotive a small boiler. All in all the size isn't that much different than that of my 5-inch GWR 14xx class loco.
