Copper doesn't really cut, it deforms! Try as I did, I couldn't get the tool sharpened to a suitable form and angle (on a "green" stone, which does grind indexable bits, albeit slowly), so that I'd get nice swarf - instead, if the feed was more than a few tenths of a mm, the copper expanded over the edge of the tool! I tried both oil and alcohol as a cutting fluid - the latter did help a bit. So, going slow and steady, and using a minuscle feed... it took me a whole day to turn the outside diameter of the flanges and bore the holes in the two tubeplates - but:
The boiler is taking shape! You can see the dry tube on top, three tube stays - which will contain a throttle rod & possibly a blower line, not that I think I'll need a blower, with the planned firing system... The hole in the middle is for the lower blowout valve for the water glass - the upper one will connect to the dry tube.
If you wonder why the color of the shell tube is slightly different from the rest - well, it is cupro-nickel! Called CuNiFer, its used in shipboard steam generators and heat exchangers, for instance. It has an annealed tensile strength two times as high as copper, is very ductile, corrosion resistant - in fact, all its properties are "better" than pure copper's, except two:
1: Heat conduction is about one tenth of copper's - but since this is the outside boiler shell, in this case it is actually better - for firebox or flues, it would be worse. Thermal expansion is only about 2% more than copper's: 17.1 um m-1 K-1 vs 16.8 for copper so I see no problem there.
2: Cost... That didn't apply in this case, though, thanks to a benefactor... :-)
Tomorrow, I'll start turning some fittings of bronze for the water glass, steam manifolds (one at each end of the boiler), feedwater inlet blowout cock and steam dome. After that, it'll be time for some hot work, silver soldering the whole kaboodle...
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