The boiler of the T3 is cladded with an 0.8 mm brass sheet. Cladding was done on real locomotives to prevent heat loss, for fixing pipes and hand rails without having to drill into the boiler shell and of-course for appearance of the boiler (all the stay bolts are out of sight and the boiler could be nicely painted).
The steel smokebox ring was use as a template for making the crinolines to the correct diameter.
The 1 mm thick rings were made to the dimension of outside diameter of boiler, minus 2 times the sheet thickness of the cladding.
Brass studs were riveted on the crinolines to keep the correct distance to the boiler shell.
Because the correct diameter of copper pipe to make boiler wasn't available (140mm), the next best choice was a smaller diameter of 133 mm. This means that I can now use an isolation thickness of 10 mm. With the cladding the boiler comes to the original diameter for the model
4 crinolines were made to support the shell.
For the backhead a 1 mm copper plate was made on a former.
The backhead plate and crinolines ready for taking up the cladding.
The firebox cladding was rolled up in the bending rolls. Pencil lines were drawn on the inside, to mark half of the circumference, so I knew where to stop with rolling.
A test fit on the firebox.
The main barrel was also rolled in with the roll bending machine. With two clamping straps the shell held in position for the next step,
The location for the holes of the dome and sand dome were marked out.
With the Proxxon tool and a small cutting blade the holes were cut.
Some duct tape was put on the sheet, so that a slip of the cutting blade, would not destroy the surface finish of the plate. The exact diameter was made with a half round file.
With boiler bands the shell is held in position. These are made of 0.5 mm brass sheet, cut to a width of 7 mm. At both ends a bracket was soldered on to take up a M3 nut and bolt, which tie the band together.
At the bottom, a small recess is cut, needed for clearance of the weigh shaft. The boiler on a T3 sits relatively low on the frames. (an extra bracket was soldered direct to the boiler shell, for giving support to the cut gap)
A test fitting on the frame. The dark blue plastic part is 3D printed and will be a model for me for making the outer dome ring from brass.
I still have to figure out what kind of (if any) insulation material I can use for the boiler. With 10 mm of space (fairly large for a model), I could use some glass wool or something similar, but maybe cork, balsa wood or a modern asbestos replacement material could be used. Suggestions are welcome.
Insulation is needed, because the boiler is relatively close to the water tanks, and water within should stay as cool as possible, for the injector to work fine.
Update:
After some advise that I got via a German live steam forum, I decided for cork. This is a relatively easy to work material, with a good insulation capacity (Lambda of λ cork 0,038 to 0,040 W/mK ) and it has resistance to moisture and rot. I've bought 3 mm thick Cork on the roll online which was delivered within two days. In several layers I can now insulate the boiler.