My tube sheets are 1/8" copper. This is pretty standard for a 1" scale loco. The main barrel of the boiler is 5" diameter by 19" long.jscarmozza wrote: ↑Thu Dec 24, 2020 10:38 am Builder, just out of curiosity, what scale is the boiler and the thickness of the copper sheet you're forming? How frequently do you anneal the copper to get those nicely formed corners? You're doing nice work. My buddy and I have been discussing boiler making quite a bit lately and he finally confessed that he's considering making a replacement boiler for a 1" Tom Thumb that's he has. Thanks, John
I use a plastic hammer/mallet to form the sheets. Rawhide would also work fine. The frequency of annealing is determined by how the copper is reacting to work hardening from the forming process. gwrdriver's advice is all very good. When the copper stops moving with normal blows, it is time to anneal. Annealed copper feels like lead to me when you first start working it, it is dead soft. Then, it starts to stiffen. It is not hard to tell. Don't continue to beat on work hardened copper, it will crack. I annealed my tube sheets probably at least 10 times to bring them to shape, probably more than I needed. I never pushed them when they started to work harden. The process was quite satisfying bringing a completely flat piece of copper into a complex shape using nothing more than a wooden former, a big torch, and a soft hammer.
If you use steel for a inside former, you will need to make the radius on the corner of the former for the sheet to follow. With a wooden former, it is pretty easy to run a radius router bit around the edge of the former. With steel, you will have to do it by hand or CNC. I have no CNC, so, maple wood was quick and effective. The British model engineers have done it this way for many years, I figured I could too!