The inner wrapper of the saddle tank for my loco is a half cylinder of approximately 7 1/4" (184mm) diameter. This wrapper is 20swg (0.036" - approx. 0.92mm) brass and is to be attached to the vertical ends of the tank. It is possible, but not at all easy, to make the tank ends as flanged plates. The problem is cosmetic. The finished end plates must retain a true flat surface and the flanges need to be at sharp and true right angles to this surface.
A simple alternative way of achieving a water-tight attachment of the wrapper to the plain flat end plates would be a pair brass or bronze half-rings with the inside faces finished to the required diameter. The half-rings need to be a minimum of 5/16" (8mm) thick (inside face and one flat face).
It occurs to me that a model locomotive copper boiler foundation ring might serve my purpose and, as such, it would be in the catalogue of one of the castings suppliers. Does anyone know of a published design which has a boiler outside diameter in the region of 7.25".
Any other ideas?
P.S. If anyone should wish to know what an 'Alice' looks like try a Google images search using the key words 'Alice' and 'Hunslet' .