Flanging boiler plates

[modeng2000]

What are the basic rules to follow when making formers for flanging copper boiler end plates? Does the flange end up the same thickness as it was before it is formed?
I am wondering how much to adjust for the former size wrt the final plate dimensions, both for normal and reverse flanges.

John

[cplmickey]

I've always assumed the flange is the same thickness as the original material. OK I suppose it's bound to be slightly thinner due to hitting it with a hammer but I don't recall much of a change. But that assumption will be fine with respect to the former as you will make the plate fit the wrapper anyway before soldering together.

[modeng2000]

Thanks for that, much as I suspected.
I was worrying about making the formers too small but I can always take a bit off if I err on the side of caution.

John

[baggo]

Hi John,

I make the smokebox tubeplate former a bit oversize and then skim the finished plate in the lathe to a good fit in the barrel.

John

[modeng2000]

Thanks John, I have seen folk say that is what that they have done but I'll have to be careful not to take much off! This is very much a 'find out as I go' job.

John

[Deleted]

The flange will usually end up a bit thicker than the original plate because you are forcing the material at the outside of the disc down to the smaller diameter of the former. Its not a lot, but it gives you a bit of material to play with when you reduce it to fit the tube. Don't forget the extra bit of clearance to give somewhere for the silver solder to flow. I've never found the need to set the plate up in the lathe to skim it, a lick round on the linisher appearing to be adequate. Seems to leave a good surface for the silver solder, too. A few centre pops around the flange maintain an even clearance for the solder. The linisher works equally well on non-circular plates such as tube plates and backheads.

[modeng2000]

I know about the centre pop idea and about leaving a gap for the silver solder to penetrate through the joint. I have a reverse flange to form and so I suppose this might end up a little thinner. I can adjust the former if needs be. The linisher sounds a good idea and no need to get things centred!

John

[Shawki Shlemon]

I guess you are talking about the throat plate , on this one leave extra materials on the sides , for some reason when doing the reverse flanges the material disappears , don"t ask me how I know that ;D , I am not answering . Trim extra later .

[modeng2000]

Thanks Shawki,
That is just the sort of thing that I have been wondering about. I would much prefer not to find out the hard way I thought I'd keep things simple by making a Toby loco, it's boiler and firebox wrapper are circular.

I am making the formers and did not realise just how tough the edges of flame cut steel can become. I used a carbide tipped tool and that lost it's edge.

John

[jgb7573]

The trick with a double flanged throatplate is to make the flange for the boiler barrel first. You do this by clamping the copper on to a flat former and then flanging into a suitable sized hole. When that's done, turn up a disk the same size as the hole in the flanged plate and fix that to the former for the outside shape of the throatplate. That'll locate the boiler tube flange relative to the firebox wrapper flange. You can then flange the outside of the throatplate. Lots of annealing!

[Jim]

Thanks jgb,
I'm about to tackle that very task in making Boadicea's throat plate and was just settling back with a soothing ale to consider the steps needed when right on cue you have supplied that answer
Much appreciated.
Jim

[modeng2000]

Thanks jgb, I'll work along the lines you suggest. Like most things, it seems easy when you know how.

John

[modeng2000]

What would be a sensible bend radius for the flanges in 2.5mm copper please?

John

[rodwilson]

Mine were no more than 3/32" internal. Worked surprizingly well.

[modeng2000]

Thanks Rod, it seems that the radius is about the same as the material thickness.

John

[Shawki Shlemon]

In our code minimum radius is 1t (which is material thickness ), but remember that is minimum , if it is more does not matter .

[modeng2000]

Thanks Shawki, that makes a lot of sense. I will have a chance to talk with the boiler inspector soon.

John

[modeng2000]

Just thought I'd let you all know how I got on following your advice.

Not having formed boiler flanges before I was a bit unsure how the 2.5mm copper would behave. But I needn't have worried, when annealed it took up the required shape with 6 heatings.

I estimated the required sizes for the formers by trying to make allowance for the flanges and clearance for the silver solder. One of the circular formers needed a bit off the diameter to bring the plate to size. The flange corner radius being the same as the sheet thickness worked really well.

John