Smoke box best way too make

Hi gents. I need to manufacture a smoke box. It’s 14cm Día 20cm long and 2mm thick. I can’t find a tube at a reasonable price this size so I need to make from flat. With this in mind I am thinking of a split smoke box to make it easier to work on the pipe work later.
however there is a problem, I don’t have access to sheet metal rollers bar a small warco one, that I don’t believe would be up to the job. So is there any way that I can roll this metal that works. Thanks

I hammer the sheet over a smaller diameter former. At the moment I have completed one for a 3 1/2 inch loco and partly finished one for a 5 inch in 3mm steel, just need to join up the ends. Prior to silver soldering I put a joint plate over the joint and screw it together.

You could buy a slice of 5" tube, cut a piece out and close it up then solder the joint. A bit of final working will get it round

One other method is the 3 point one where you press the strip of metal between formers that just need to be a bit of bar, two on one side and one in the middle on the opposite side of a vice and work along just nipping up the vice to add a slight bend

All rounded edges would be better to avoid the slight marks you may be able to see here

Hi Michael its times like this belonging to a club helps, my club have a set and at least two members me being one. Iam on the cambs essex suffolk boarder if it is any use.

Paul

just looking and you can get 4.5" OD ERW tube x 2mm wall that's 114mm OD, saw through it and add a piece to increase the dia may be easier than reducing a larger bit.

Or if you want it in two pieces then cut two bits just over half circumference and open them out a bit.

Find a local sheet metal man, the guys round here will do little jobs like that for a contribution to the tea fund. If rolling in 2 halves leave some excess, the ends are usually straight if using pyramid rolls. Why does it need to be so thick?

Some food for thought. Paul, I am a member of a club, however they don’t do anything which is sad I know.

I did a 6" dia by 3 5/16" wide out of 3mm steel with a 300mm 3 in 1 roller, cutter, bender.

You do it in very small steps as the gears don't reach each other. You do not need to use tools on the roller wingnuts to get drive and don't extend the handle. You might get away with twice the length as yours is only 2mm.

If it won't work nothing is lost as long as you didn't force it.

Ok, I have rolled the cylinder and it came out nicely to size. Now can anyone please let me know a good way to set the ring of rivers in the cylinder without using a dividing head which I don’t own. Thanks

preferably using the CAD draw a row of crosses on paper spaced apart by the arc length between rivets. Cut it out and stick it to the smokebox with PritStick. The arc length is d=OD*pi/(number of rivets). This is unlikely to be anything like a sensible number, hence the use of CAD. You can reduce cumulative error by dimensioning all the crosses from zero, ie 0, d, 2d, 3d etc

Edited By duncan webster on 04/09/2023 12:48:57

You could use a dressmaking tape that is flexible or just wrap a piece of suitably marked paper around it. If it will fit on a lathe then you could use the gears on the lathe to divide it up. If that is possible let us know and we can show you how to do it.

Thanks buffer, great idea. I know how to use the lathe gears, but my head was thinking milling machine. The lathe would be a lot better. Thanks again.

One more great idea, thanks again.

Wrap paper strip round and cut to exact length, lay out flat and measure then divide into convenient divisions refit to smokebox and use marks for drilling.

LBSC once recommended forming the smokebox around a drainpipe. I assume that in his day that meant a traditional cast iron one!

Neil

Thanks chaps, I was able to form the smoke box, I used solidworks to do all the calculations and marking out for the hole positions etc. then purchased myself a better set of rollers. Came out 100 perfect. Thanks for your support

On dividing a cylinder for rivet holes and the like without a rotary table, Try this:

A similar problem when needing make a strainer: lots of rings of holes, divided along and round.

You may need exchange a quick-change tool-post for a conventional clamp type for this.

Mount a broad metal block - I think I used brass - in the lathe tool-post, square it to the chuck by simple contact, then drill a hole of the correct diameter through it at about mid-length, from the chuck.

Mount the tube between centres and fit a suitable change-wheel to the back end of the spindle to use as a division-plate. If your lathe does not lend itself readily to changing the spindle pinion you'd need use the bull-wheel or some sort of compound-dividing.

Rotate the drill-guide on the top-slide and re-clamp it square it to the work. (Simply, gently push it against the tube).

Now use a small portable drill to make the holes, with the guide in light contact with the tube.

For the strainer, I just aligned felt-tip pen marks on the change-wheel, visually, to a fixed feature; but important work like a smoke-box needs some form of positive detent. For the length division, I used the lead-screw and a second change-wheel, isolated from the spindle wheel.

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That was done on my EW lathe before that yet had proper bench to stand on (not long after I'd moved home)! I used a battery-powered drill.