Hi Lee. I have used both methods in the past. Overall silver soldered boilers in my opinion look better, but since no one actually sees most of the joints on a finished loco this is irrelevant. For longevity I would opt for tig all day as once the joint is made it will not change no matter what you throw at it. I opted to silver solder the tubes in just to make life easier for me. Tell the inspector of your plans and ask if he requires anything special – I don't have the exact dims for your boiler but it may well fall into the category which does not have ce certification so be aware of this. My commercially available 3" dia boilers are all silver soldered purely because of customer expectation but if i were making one for my own use it would be tig.

Tig would be a complete fusion of the joint,if done correctly .where as silver solder is simply a "glue" at microscopic level.A TIG welded joint will out perform silver soldered in all tests.

I think that you need to discuss this with a boiler inspector and insurance company before doing anything if you are considering using the boiler in public.

Brian

This can become an emotive subject

It seems to me that getting on for 100 years of experience has shown that the silver soldering of copper boilers for model locomotives is a system that is tolerant of technique and material quality – an amateur has a very good chance of making a satisfactory boiler, mainly, I think, because the capilliary technique of silver soldering means that a simple visual inspection shows whether a joint is sound. It may not be the best technique but it is good enough, as proven by the 2x hydraulic proof test.

With welding; more skill is required to ensure a good joint, visual inspection is no guarantee of good technique and material certification, because of the risk of hydrogen embrittlement, is required. A more robust form of certification is therefore necessary and generally means that welding is best left to the professionals.

Sadly, this seems to mean that the cost savings of not using all that silver solder are offset by the requirement to maintain accreditation and certification

As far as longevity is concerned I'm not sure that joint failure is the major cause of the demise of copper boilers, more likely to be erosion of the tubes, particularly at the fire-box end – perhaps others with more experience could comment on this.

If I was buying a complete boiler I would go for either. If making my own it has to be silver solder.

2p's worth

Rod

Hi Lee,

As someone who has made a Boxhill boiler recently in 5"g perhaps I might add a few comments.

(Mine differs from the original what I consider to be defective design by Martin Evans).

The Martin Evans design was during his early 'experimental' period when he really pushed the boundaries as to what had been acceptable before for boilers hence no crown stays fixed to the outer firebox wrapper etc. The inner firebox wrapper is far too thin for my liking. The water gauge bottom bush is far too low. None of the backhead fittings are in the right place for fullsize.

There are lots of pics in my albums of my own boiler build with correct oblong firehole ring as per original and 2 water gauges.

For TIG welding the whole boiler design needs looking at and redesigning to give the proper joints required for TIG welds plus the correct grade of copper needs using. This will require almost certainly a joint on the barrel longitudinally as the barrel will have to be made out of sheet copper of deoxidised sheet.

This barrel joint might conflict with the very close weighshaft of the valve gear.

I could only get C101 copper tube for my boiler barrel of 3 3/4" dia, which also was split to form the firebox with only an outer firebox extension added on the right hand side (Evans' design called for an extension on each side).

I also fitted in 2 extra ordinary flues.

Mine has the correct to prototype oblong firebox hole ring and correct Stroudley firehole door.

I think a much neater boiler is produced by silver soldering than TIG, which in the case of Boxhill might be quite important. For example in fullsize there is a generous radius on the backhead flange not followed by Martin Evans but which I endeavoured to replicate. This would not be possible I suggest with a TIG welded boiler.

It is quite a simple boiler to build as a silver soldered job.

I do not disagree with any of the previous posters comments.

Cheers,

Julian

Edited By julian atkins on 28/01/2017 23:31:30

Hi Lee,

I also incorporated a double flanged throatplate to mine which is I consider a considerable improvement to the original design.

The backhead and throatplate and firebox sides could also do with far more stays which I added compared to the original design. A commercial boiler maker of repute will add these as a matter of course.

Cheers,

Julian

Edited By julian atkins on 29/01/2017 00:31:05

I agree, it would certainly be a lot easier if you could just weld everything, but I suppose it's about what kind of equipment you have to hand, welding is a big initial outlay of cost and a bit of step in the dark for some people.

Like you said, the shell will fail before a weld will.

Whereas silver soldering can be achieved with a relatively inexpensive burner, even if the solder can be on the expensive side sometimes, it feels like a more familiar process,

and last but not least it teaches you good overall metal joining practice. You need to always ensure the join is on fresh, exposed and clean metal, flux it up and give it a space to run in between. You could lay down a weld with a M.I.G unit and not really be aware of what's going on, even if it's a good weld.

Also sorry to Fizzy, I didn't intend to embarrass or "make a spectacle", I was just curious, tha'ss all.

Michael W

Edited By Michael-w on 29/01/2017 12:23:41

Superb looking boiler, Julian.

Michael W

Thank you very Michael for your kind words.

It is silver soldered throughout including all the stays.

For Lee to get his Boxhill type boiler TIG welded it will have to be re-designed. This is quite an awkward process in many clubs, unless undertaken by the commercial builder. I have seen lots of commercial Simplex and Rob Roy boilers TIG welded but not a Boxhill yet.

I dont have a problem with a TIG welded boiler per se, but in the case of Boxhill it just wont look right!

After all, when driving the bit you look at most is the backhead, and it ought to look right. I dont really want to look at an ugly TIG welded joint on the backhead.

Hopefully Lee will comment further as the OP.

Cheers,

Julian

Happened across these photos of a welded model boiler today which just goes to show you can have radiused backheads and throatplates on a welded boiler, this is steel but should not be a problem to do it with copper.

Interesting video of the backheads being pressed, you will need a bit more than a MAPP gas blowlanp and bench vice to press these 3/8" plates

Edited By JasonB on 21/02/2017 15:52:59