Rob Roy boiler; help needed.

[Anthony TauntonParticipant @anthonytaunton43819]

Slowly moving towards the first silver soldering steps in my Rob Roy. I have built water tube marine boilers in the past, but never a loco boiler. I have the firebox tubeplate and the backplate and the wrapper screwed together temporarily with 10BA screws (will use rivets when soldering). All good. I will use high melting point silver solder for this. The thing I'm anxious about is setting the physical relationship between the firebox and the boiler shell and the smokebox tubeplate, in order to get the tubes to achieve this 3/32" gradient rise between the firebox tubeplate and the smokebox tubeplate. The lower two tubes, on the drawing, are shown as just a small unspecified distance above the throatplate. Roughly, what should I aim for?

I intend to build a makeshift jig to lock the firebox and the smokebox tubeplate together in their correct relative positions so I can silver solder the tubes in the f/b tubeplate to achieve the correct gradient. This seems the obvious way to do it?

Also is it better to use rod-type stays for the top of firebox rather than the original girder stays?

Thanks.

[Anthony TauntonParticipant @anthonytaunton43819]

[Phil H1Participant @philh196021]

Anthony,

In the mid 1980s, I made the huge mistake of building a Rob Roy boiler to the old 1960s design without the input from my local club. Your questions suggest that you might be about to make the same or at least similar mistake because even my modified Rob Roy boiler drawing in the Rob Roy and William book is not up to date .

Please, please pause a moment and speak to your local club inspector if you haven't already done that. They will give massive amounts of advice and tips on how to avoid some of the pitfalls and they will make sure you make the necessary modifications e.g., the correct silver soldered top fitting for the water gauge.

Loads of people will give advice here – but please see your inspector first.

Phil H

[J HancockParticipant @jhancock95746]

As above , plus the correct sequence of 'assembly' is vital , one wrong step guarantees major problems further down the line.

[Jon LawesParticipant @jonlawes51698]

Whatever you do make sure your club boiler inspector has seen it before you go any further, not only will they be far happier signing off something they have seen themselves they will have lots of good tips and advice. This could save you a lot of expense and heartache further down the line.

[Phil H1Participant @philh196021]

Anthony,

Additional… There are some really good locomotive boiler build threads on the proboards model engineering site.

There is quite a recent 5" gauge Britannia boiler build (over the past few years) and Julians 5" gauge Terrier/Boxhill type locomotive boiler build. Both threads are excellent and show the boilers being build up from scratch including plate flanging etc.

The Britannia build also gives information on the sizes of Sievert torch and nozzle sizes, along with other silver soldering kit information.

From memory, the Britannia builder struggled when he tried to use 'loose' rivets as you suggest and he found that bronze screws were more successful.

I think most people seem to struggle more with the high melting temperature silver solder and they seem to reserve its use for the smaller fabrications rather than trying to use it for the larger, first stage soldering steps. I think most people try to use the lower temperature solders and use shielding techniques to prevent the melting of previous work. I suppose it depends how experienced you are with silver soldering and what heating kit you have available.

Hope that helps.

Phil H

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