There are a number of calculations that will need to be done to work out the copper thicknesses, it would be impossible for anyone to give a thickness off the top of their head without knowing things like size, working pressure, etc.

Best thing to do is get a copy of Martin Evans book on locomotive & marine boilers as that will have the formulas that your boiler inspector will want to see and be using as his guidelines.

It may well be that you will have to make some allowance for practicallity over scale appearance or at least have some dummy parts, just looking at your very impressively modeled engine the large flat areas of the firebox backhead and end of the boiler barrel will not be acceptable without some form of stays to support them.

Yes you can make your own boiler but before you start to cut metal join a club and get their boiler inspector to look over the drawings and he will also say at wat stages he wants to inspect the work.

J

Edited By JasonB on 02/12/2014 08:05:50

hi neal,

as a first build a 7.25"g Rocket is far from ideal.

if you are attempting a scale version there are a great many unusual factors to be considered.

the boiler is a structural component as the loco does not have frames. everything is bolted to the boiler. this complicates things and is an additional factor that needs input into the design and calculations (though i suppose is what the traction engine lads have to do anyway).

the firebox is very unusual being in effect a separate component with an outer water jacket connected by pipes to the boiler. the throatplate and backhead are 'dry' and may originally have been just firebrick.

the way the loco valve gear is operated is by a complicated system of foot pedals and requires manipulation of the valves by hand initially. to my mind not incorporating the correct valve gear makes the loco nothing like the original. however the way of operating the gear makes it extremely difficult in miniature, if not impossible.

the driving wheels are wooden and will require a considerable degree of wood working skill to make them properly and accurately.

the cylinders have a very short valve chest with very long passages. this would be (as was the case in fullsize) a pattern maker's and foundry man's nightmare. even if built up and fabricated they would still be a very complex job.

cheers,

julian

And just so you don't get put off here is a nice one, notice the photo of it working with two people behind

Couple more shots on page 5 of this album and also some other early style locos on this page

Edited By JasonB on 02/12/2014 11:20:15