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Material for smoke boxes

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michael bird22/02/2011 15:50:18
22 forum posts
9 photos
Hi all,
For the smoke box (the how to book) tells me that I need a 2.1/2" long piece of steel tube to finish at 4.1/8" diameter with a minimum wall thickness of 3/32".
Has anybody any ideas where on earth I can find such a piece or even a solid chunk that I can bore out?
Hope you can help,
DMB22/02/2011 16:01:33
958 forum posts
Hi Michael,
Obtain a piece of steel sheet and roll it. Probably comes only in metric thickness - 2 or 3mm? No rollers? do you know a club member who will do it for you? Alternatively, pay a supplier to roll and braze it. Blackgates used to do this service but it is an expensive option.
Phil Ashman22/02/2011 16:31:16
33 forum posts
My smokebox is rolled from a piece of sheet, but if I were doing it again I'd use a piece of tube if possible. Although it looks perfectly round, it isn't quite, so I had troubles getting the chimney, saddle, and door ring to fit snugly. Mine's made of brass, so there's some give in it, but I reckon you could have quite a struggle getting a door ring into a steel tube that wasn't quite round.
colin hawes22/02/2011 16:44:37
502 forum posts
18 photos
Hi Michael, Note that if you roll a tube the job will probably have a flat at the start so roll an overlap so you can saw the starting flat off.
JasonB22/02/2011 16:46:26
17066 forum posts
1839 photos
1 articles
If you can't roll it yourself then try these people.
Its usual to roll and weld a TE smokebox, thats how mine is done. Unfortunately your size cannot be turned from Round hollow section or API schedule tube. 2.5mm sheet is available and would do for 3/32"
mgj22/02/2011 18:18:53
1008 forum posts
14 photos
And mine - I just got a local engineering firm to roll it up out 3mm - 1/8 steel, plus folding the perch bracket and I MIGed it up. Rivets and dummy plates concealed the weld, so it looks propely riveted. whole lot cost £15.
Then the rings, I just turned them till they were a snug fit, and welded them in, though SS would work, and then dummy rivets. Of course with welding nothing will be round round, so I just turned the ID to the right dimension, such that it was snug over the boiler, and that black graphite goo does the rest.
The little loco is even easier since the smokebox is rolled and silver soldered in brass. I'll turn the rings, and go to a heating firm to get a couple of large jubilee clips and wind that round the box while I SS the gunmetal rings in - I don't know what ss alloy they used but I'm assuming EF or AG2. Then turn to dimension/round in the 4 jaw. Being a copper boiler, the rivents won't be dummies.
I'm rather conscious that I at least am not trying to build the engines for Saturn V. Merely hanging grimly on to the trailing edge of technology. As long as it looks (very) decent, the door opens and its all airtight, more is not really necessary?

Nicholas Farr22/02/2011 20:42:34
2067 forum posts
995 photos
Hi, when rolling hot rolled steel into a cylinder, it is always best to roll a slight curve, then turn it over and roll the curve to other way and then finally turn it back to the side you strated on to roll your cylinder. This method breaks the suface grain structure stresses, from the manufacturing process and gives a much truer roundness in your finished cylinder.
The type of rolls will depend on how much flat portion there is at the beginning and end of the roll. Pyramid rolls will always have a largish flate portion at both the beginnig and end of the roll and an allowance will have to be made in the length of the material from the start if you intend to cut these off to avoid having a flat place that you then have to deal with. The other method is to shape the ends to the correct radius prior to rolling.
In fabrication shops this is normally done by nipping it in the rolls with the edge of the plate just over hanging the bottom roll and then hammering it along its length, then advancing it sligtly and repeating a few times until you get the correct shape using a profile gauge for the length requiered for the rolls you are using. It is then rolled through and the other end is given the same treatment. When both ends have been done, it is removed from the rolls and turned over and then rolled to shape. This method saves on material, but is a little time consuming.
Pinch rolls are not supposed to leave any flat at the start or finish of the roll, but I haven't used a set that actually does this, so one of the above methods may have to be used, but the portion won't be as long.
Once your cylinder has been rolled and the joint welded, and with the weld dressed, it can be returned to the rolls and be slightly over rolled for a couple of revs' to take out any ovalness that may be presant if needed.
Regards Nick.

Edited By Nicholas Farr on 22/02/2011 20:45:16

michael bird01/03/2011 07:27:18
22 forum posts
9 photos
Sorry for the delay but can I now thank you all for your help and guidance. A special thank you to Jason for giving me the link to Feraday Cylinders. Nice people, have ordered one, job done.
Regards Mick
DMB01/03/2011 09:17:12
958 forum posts
Hi Phil,
I admit that my rolled - sheet Sweet Pea smokebox looks round until, like you say you put the turned rings in each end. When I finally fix them, I will bung up the small gaps with Bosswhite or similar `gunge` and paint over with heat - resistant black paint sold for i.c. engine manifolds.
mgj01/03/2011 17:44:07
1008 forum posts
14 photos
You may well find if one is not over enthusiastic about turning to dimension, that with a light tap fit you will bring it round, or pretty nearly so.

Mine is Metre Maid, so its the same tube and probalby the same source. I shall just bevel an edge a tad and silver solder.

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