Boiler flanging plates

[Peter Simpson 1Participant @petersimpson1]

Hi All

I intend to make a couple of forming plates to make the front tube plate for my boiler. The OD of the boiler is 41/2" in diameter and the the wall thickness is 2mm Should the diameter of the forming plate be 41/2" minus 4mm ? Or is there an allowance made for fabrication.

[Peter Simpson 1Participant @petersimpson1]

[Brian HParticipant @brianh50089]

If you are using copper, well annealed, you will likely find that the flanged part will increase in thickness. I always use no allowance and then turn down the flange until it is a nice easy fit in the barrel tube. It is important to allow a small gap for the solder to run into.

Brian

[Mike Henderson 1Participant @mikehenderson1]

Like Brian, l make no allowance on the flanging former for the fabrication but there is one thing you seem to be missing.

Former diameter should be the barrel outside diameter minus twice the wall thickness of the barrel minus twice the thickness of the material you're using for the endplates. I suspect this was just an oversight but Peter's calculation gives the former a diameter equal to barrel i/d.

Regards, Mike

[Peter Simpson 1Participant @petersimpson1]

Mike I had a Saturday morning senior moment and missed out the thickness if the tube plate flange thickness, But thanks for confirming the forming plate dimensions.

Peter

[Clive Brown 1Participant @clivebrown1]

I'd agree with the above. I've just measured a flanged plate that I made a few weeks ago from 3mm copper. The flange is barely thicker than the original thickness. Perhaps 3 0r 4 thou. at most, which gives a bit of an allowance for smoothing down the hammer marks with a file.

[Speedy Builder5Participant @speedybuilder5]

I flanged the 10 gauge plates for a 5" gauge boiler made of stainless steel using JABROCK – much easier to work than steel formers. May be able to find chunks of it on auction sites

JABROCK

The boiler was subsequently scrapped as no inspector was prepared to inspect it due to the fear of crystalline cracking over its lifetime. I believe the AUSTRALIAN regs now allow SS.

[Nigel Graham 2Participant @nigelgraham2]

I am sorry about your disappointment Speedy Builder, but (and here I'm assuming you are in Britain) it's a pity you did not obtain a copy of the MELG boiler-test booklet right at the start.

For that scheme specifically excludes "stainless-steel" for boilers. I don't think it states a reason, just a blanket ban

I would advise anyone making a miniature steam boiler to buy a copy, even if buying a commercially-made copper boiler to a published design. Or at least, if in a model-engineering society, the club should have a copy for members' use. .

If you had asked a commercial rather than club boiler-inspector he would probably have insisted on being sure of the grade of steel.

'

Fundamentally there is no reason not to use stainless-steel for boilers, but it would have to be of one of the correct alloys because stainless-steel comes in very many flavours of three primary groups. They are so varied to suit different classes of application and different fabrication methods – including pressure-vessels for very critical uses indeed.

Yes, our Australian and New Zealand, and I think Dutch, colleagues have found stainless-steel alloys suitable for small boilers; but our insurers are still too nervous about it.

[Brian HParticipant @brianh50089]

I can confirm that Jabrock is excellent for short term use for forming metals. I used to work at an aero manufacturer that used lot of it and I still have some small pieces.

I also made a stainless boiler, for a 5" Boxhill and realised afterwards that It would not be passed for use. I also made the rolling chassis, the cab and the side tanks out of stainless because there was so much of it available as scrap whereas mild steel was very difficult to obtain at this company..

Brian

Edited By Brian H on 13/03/2021 13:10:44

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