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Soldering a front tube plate

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John Billard 118/10/2021 15:14:54
108 forum posts

All the references I have seen advise that a front tube plate should be driven into the boiler shell before soldering. What about the capillary gap? Do we rely on the boiler shell expanding?

John B

Clive Brown 118/10/2021 15:55:24
807 forum posts
39 photos

The shell expansion would presumaby be matched by the tube-plate expanding a similar amount. I haven't seen provision of a gap as an issue in boilers I've made. More like getting the tube-plate a reasonably close fit in the shell. If a capillary gap was seen to be needed then filing a very shallow taper around the tube-plate flange would suffice in my view.

John Billard 118/10/2021 20:29:21
108 forum posts

Thanks Clive. Presumably the tube plate is sealed by a fillet of solder. In any case I accept that if there was a gap it would be difficult to maintain it.

Kind regards

John B

noel shelley18/10/2021 20:48:27
1281 forum posts
21 photos

Not sure of the wisdom of a drive fit ? If heating is correct then the capilliary and surface tension will pull the tube plate into the centre and maintain an equal gap all round, all be it only may be 3 or 4 thou. The harder part is to hold the tube plate in place in the shell, there are many ways. If the soldering is sound there will be a very small fillet, the joint will be filled by solder and therefore steam tight. Good luck Noel.

Grindstone Cowboy18/10/2021 21:18:32
854 forum posts
64 photos

Never built a boiler myself, but have been following the Blondihacks Youtube series on making a vertical boiler. She made the tube plate a loose fit and used pins to hold it in place whilst soldering - for example here.


fizzy18/10/2021 21:31:36
1841 forum posts
120 photos

Yes, maintain a slight interferance fit. There will be plenty of so called gap for the solder to penetrate the joint. Whatever you do dont try to manufacture a gap. How can I be sure of this? I make boilers for a living and have never had a joint faiulre - ever (having made hundreds of them). Anyone wanting to learn is very welcome to come visit me as Pendle Steam Boilers in sunny Burnley.

John Billard 118/10/2021 21:32:03
108 forum posts

Thanks Noel

You are quite right about a drive fit. What if it goes in awry and how do you retrieve it without damage?

Thanks Rob

The Blondihacks viewing is compulsory particularly as she is so honest about how it went wrong.

John B

John Billard 119/10/2021 12:59:29
108 forum posts

Thanks Fizzy, for sharing your experience. Thanks for the invitation! I am near Reading, but if I the the chance....

John B

fizzy19/10/2021 14:01:43
1841 forum posts
120 photos

No problem John. If you want any one to one advice feel free to contact me via my website **LINK**

John Billard 119/10/2021 15:33:16
108 forum posts

Thanks Fizzy

All going well so far, but you never know! Tubes soldered in to the firebox tube plate and firebox outer wrapper soldered to the barrel using 424 and 430.


Speedy Builder519/10/2021 16:43:54
2592 forum posts
207 photos

Nice video Blondihacks. Question: What is the black flux she was using. I have seen White, pink, but never black.


Grindstone Cowboy19/10/2021 16:57:22
854 forum posts
64 photos

The flux is Stay-Silv Black by Harris Products apparently - I found their website here. Don't know if it's available in the UK though. She mentions it contains boron to extend the temperature range.

Links to


fizzy19/10/2021 17:33:55
1841 forum posts
120 photos

The flux is available from the cup twins... I use it as a base and mix other fluxes with it to get the grade I like. It lasts a very long time and goes a very long way. Regarding the video - putting my neck on the tracks here but it is a video of how not to solder a boiler. Follow it at your perril - nuff said. Think Eutectic.

John Billard 119/10/2021 17:58:34
108 forum posts

Yes, this what I am using. Very impressive. As Fizzy says lasts a long time under the torch at high temp for the 424.

Regarding Blondihacks yes plenty of errors there but she admits them.


John B

Bill Phinn19/10/2021 21:21:07
732 forum posts
103 photos
Posted by fizzy on 19/10/2021 17:33:55:

The flux is available from the cup twins...

Please could you provide a link for the flux.

fizzy19/10/2021 21:31:34
1841 forum posts
120 photos

strangely its not on the cup website - but thats where i get mine from - I bulk order so dont go via the website

Luker20/10/2021 07:20:07
160 forum posts
116 photos
Posted by fizzy on 19/10/2021 17:33:55:

Regarding the video - putting my neck on the tracks here but it is a video of how not to solder a boiler. Follow it at your perril - nuff said. Think Eutectic.

Hi Fizzy, I watched the second video of Blondihacks and I thought the end result came out ok. I'm a little curious as to what you mean by eutectic?

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