Further reading and exploring web sites, email to London Science Museum (LSM), asking opinions of boiler experts. Even considering a quick trip to London. (from Oz).
What I have learned is interesting.
Richard Trevithick did not manufacture any of the several hundred of his high-pressure engines. The ideas and designs were his, but the engines were manufactured in different sites and by different makers. The designs changed with time and as new ideas presented themselves to the brilliant mind of Trevithick. And each manufacturer put their own stamp on the designs.
For example, look at the following pictures of the boiler flat end plate. One is in two pieces, riveted together. The other is a casting, and the flanges for the inspection hatch and the chimney, and probably the blowdown valve orifice, are almost certainly part of the end plate casting. The firebox looks newish, slipped inside the original end plate casting. I guess that the original firebox had burnt out, but was probably similarly held in place. If any Brit readers can pop into the LSM and check this out I would be very grateful.
The model which I am making, and dithering over the end plate design, is based on the reconstructed engine in the London Science Museum. I intend to remove the aspects which are obviously Victorian in origin, and replace those with parts that I think will be closer to the Trevithick era designs.
Unfortunately, I have already made some of those parts, so my redesign is a bit compromised, unless I scrap them. Which I do not intend to do.
So this is my redesign of the end plate. Not quite LSM. And not quite Tubal Cain/deWaal Not quite, but will have to be close enough. The red lines are already machined so I am stuck with them. 14 drilled and tapped holes have been filled. The bronze inspection hatch/plug has been made, but with less standout than shown in the lateral view.
As an aside, while pondering the end plate, I have made a start on the engine itself. The cylinder has been roughed out, and will be finished in my next workshop session. Cain specified brass, deWaal specified bronze. So I have compromised, and have used an unknown brass/bronze/copperish lump of workshop metal. It is certainly hard, as assessed by filing. Photo next post.