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SHM 26

Superstructure - Soldering the boiler in place

After construction of the boiler I let it rest a while taking advantage of the fact that the boiler could easily be placed for reviewing results and removed again to keep it out of the way of drilling and detailing activities. Once I got to the stage where I was confident that there were no more such activities I devised a way to join the boiler permantly.

Well after so much soldering getting the boiler in the right place shouldn't pose too much problems, so why this page you might wonder? Make a shot of the soldered boiler and get on with it. You're quite right, if it were that simple I would have done just that. But it wasn't that simple.

The boiler is made of solid brass. That takes a lot of heat to get anywhere near the point where the solder will flow easily. By the time you get there your carefully built-up loco wil have fallen apart because everything comes loose again by the excess heat.

So the trick is to heat the boiler in advance and then install the hot boiler in place before quickly finishing a solder seam with the soldering iron.

First position the boiler carefully in its final (resting) place. Mark this position so it will be easy to line it up quickly once the boiler is hot.

Put the boiler on its front and heat it slowly and evenly with the gas flame torch (link).

The trick now is to achieve a temperature between 140 C, the temperature at which the solder will flow, and 188C, the temperature at which the boiler appliances will start falling off.  To that end I put a scrap of 140 C solder on the boiler backhead. Once that melts it will tell me the boiler is hot enough. It is imminent though that you don’t heat the boiler backhead directly with the torch because that will cause the solder to melt immediately and give a false alarm.

The superstructure was fixed into place with four pins

The hot boiler was placed, the marking were lined up quickly and a fillet of 140 C solder was run on the inside of the cab with a hot 60 Watt soldering iron. Make sure you only touch the boiler top and not the cab’s front sheet.

Work fast but calm and determined.


Heating the boiler and then adding remaining  heat  with a soldering iron is a method that worked. BUT, it is a risky method. Everything should work the first time. What if it does not work out the way you intended and the boiler cools before you can get it out again. I would not know another method then desoldering a large portion of the superstructure and start over again.
The convincing proof: the boiler is correctly positioned within a reasonable margin. On the photo it seems to tilt a little bit to the left, but that is hardly visible from any other angle then head on
To conclude that part of the construction the smokebox was soldered to the support