Boiler wrapping petticoat.

[Michael CallaghanParticipant @michaelcallaghan68621]

Hi chaps, I would like some help. I wish to make a boiler petticoat for my Martin evans Columbia. The boiler is copper and the wrap is brass. From measurements, it looks like I need 3mm thick material for the petticoat, and I wish to screw the wrap to the petticoat to give clearer lines to the boiler. I also need to have a few strong points on the wrap for dome attachments etc.

I am thinking of making the petticoat like a set of half rounds each linking with a center piece running the whole length of the boiler cylinder each side. The think is what would be the best material to use which will be easy to roll and not react to the copper or brass.
thanks

[duncan webster 1Participant @duncanwebster1]

I suspect you mean crinoline, not petticoat, at least in UK speak

[Nigel Graham 2Participant @nigelgraham2]

On a locomotive the “petticoat”, more usually called “petticoat pipe”, is the bell-shaped inlet to the chimney.

If you use metal for the crinolines you will reduce the cladding’s effectiveness a bit. PTFE, SRBF or similar may work but determine the candidate material’s maximum working temperature first.

Of full-size boilers the hoops seem to be supported on spacers, and you might examine following suit, with PTFE, SRBP or hardwood spacers below a thin brass band on which to support the cladding sheet and its external closing bands.

I don’t know the specific design but usually the outer sheet is wrapped right round the boiler with a single longitudinal joint along the underside. It is held by narrow bands sited over the crinolines and the rim of the smokebox; each band closed by a nut and screw or a screw into a tapped bush on the band, also under the boiler. This closely replicates full-size construction.

You could split it along the horizontal centre-lines as you suggest but it would look odd, unless it was a feature of the prototype locomotive.

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The outer sheet, or wrap, is often of brass on models although it’s not the easiest metal to paint (using suitable etching primer). It can be of very thin mild-steel sheet though, preferably tinned or galvanised but certainly painted inside and out. It should not become wet inside in service, though that’s a risk if you use a safety-valve as a cold filling-plug.

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What does the designer show for fitting the outer dome, which is usually a cover over the actual steam-dome? Sometimes it is held by a small, discreet, central screw into a tapped, blind hole in the dome itself. (Not a through-hole. You don’t want a potential steam leak there.)

Small details like hand-rail stanchions and pipe-clips are secured to the wrapping sheet, perhaps also an underlying crinoline, according to the individual engine.

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