As Neil says .. Jason's the guy for that question. I suppose it also depends on whether you're planning on building your own boiler of buying in.. in which case the boiler builder may well have suitable plans they like to follow. As someone struggling to finish his own 1" minnie boiler it's been a heck of a learning curve although I'd fancy considering a crack at making a 2" boiler (for myself) with benefit of this build. Starting with a 2" boiler would have been a really expensive learning curve with some on the bog-ups I managed along the way….

Other considerations are the rear wheels at 12" won't be machined on your lathe unless you build some riser system and commercial 2" minnie gear set is a breathtaking £540 + vat and post from blackgates – although in the scheme of things that's just a small part of the total cost. (gear making is next on my list of skills to learn)

Insulation is definitely key to successful boiler making. I did a 5" loco boiler with a single 25mm dia sievert torch and an insulating chimney liner, see my album for photos.

25mm torch is about 8kw. I certainly don't have the skill or experience to use one that small but it would allow better hand access. It takes a while for me to get the whole thing to temp with pretty good insulation and a bigger burner and I still tend to run into flux exhaustion. But guys around here are pretty smart.

Vermiculite fire bricks and fire blankets cut and shaped as necessary are your friend. I tried to find his chimney liner on line..nearest i found was pumice based which is probably another form of vermiculite. I asked all the same questions last year at the beginning of my minnie thread **LINK**

There's also pics of my assorted hearth build-ups in that thread… and my errors

Julian,

I've never shied away from being criticised and yes, I do recall you offering your direct help but the whole point of this was for me to try and do it myself. If you say I'm using the wrong blocks then please provide a tradename because I'm using light, grey thermalte type blocks as the basic surround/wind break and then vermiculite immediately surrounding the boiler itself. If there's anything else specific I'm doing wrong or advice I've ignored then please share for discussion and my education.

pgk

On the question of soldering the boiler in a garage or workshop it really depends on how quickly you wish to be overcome by CO2 poisoning. The big burners needed will soon eat up all the oxygen and leave none for you!

There is the added problem of propane producing water vapour which will condense on any cold metal surfaces in your workshop and promote rust. And the last photo on this page shows what the build up of heat can do.

As for torches, I would say somethiong with a 26 or even 35Kw burner as that 4mm thick copper will take some heating, the Sievert ones are good but pays to shop around. Also worth reading the "best practice" on that site.

Since I'm obviously doing it all wrong you should ignore all my 'advice'. One of many things you will find is tthat these burners use up so much O2 that getting it close to the work doesn't leave enough access for fresh air and it flames out. I keep an ordinary small torch lit on the bench for a relight if necessary. I'd guess that a smaller torch aimed at the work with intent to keep some heat in will likely just be extinguished by the larger torch using all air

I do my soldering outside the shed door.. at night, with shed floodlight illuminating. Equally if you plan on dropping hot stuff into an acid bath then it's better done outside standing upwind unless you plan on holding your breath and escaping the shed pronto while everything in there dissolves. you also have the problem of handling annealed soft copper that's still hot.

Julian,

Please try and mind your manners.

Thank you.

Neil

Jason is quite correct in that pgk pgk is using the Celcon blocks that I use (the big grey blocks on the outside of his pic of pgk pgk's set up), but pgk pgk has used heat absorbing quite heavy vermiculite blocks around the boiler.

The celcon blocks cost a quid a piece and are also easy to cut up with an old wood saw to exact sizes to fit into the firebox etc . Had pgk pgk used just Celcon only he might have got better results. I have always silver soldered my boilers indoors with the workshop door open. A curtain covers the doors and workshop window if the sun comes out.

Celcon is not quite as good as the thermalite white blocks, but the best available atm.

Hi James, I think you have it pretty much correct except as Jason says the secondary heat. I scrub the assemblies in hot soapy water after pickling – it is amazing how much more dirt comes off on this stage. To remove hard deposits of flux I use a different method.

Cheers,

Julian

I knew julian favoured thermalite type blocks but wasn't aware of the anti-using firebricks inside. Indeed as Rod points out they are used /sold as brazing hearths and in the woodburner industry commenst such as needing them to act as liners to prevent the ast or steel becoming too hot.

BUT stirred into thinklng about it.. Yes, they do get hot so they aren't acting that well as insulation and therefore adding to the mass of heatsink one is pouring the therms into. That could have some benefits in terms of storing heat and keeping the item towards temperature but equally the extra time involved has to add to flux exhaustion and leads on to some other thoughts I'd had the other day when working just on one part of my boiler as to whether there may be benefit in heating from the end I had totally enclosed (as in open a window there) so one can raise basic temp of the item without directing the high temp at the flux until necessary….

…I suspect that's what they call experience…

pgk

Dave,

These are vermiculite wood-burner type liner blocks cut from vermiculite board.. not the same as the sort of stuff old pizza ovens are built from that can just cope with the heat cycles without cracking like ordinary house bricks. However I have no doubt that spun as rockwool is way better