Silver soldering a Minnie traction engine boiler

[Jeff DaymanParticipant @jeffdayman43397]

Paul – I agree with your points. Before any mods to any proven existing boiler design a detailed analysis is needed, with design and stress calculations. Any proposed mods should be reviewed with the local boiler tester for safety. Hunches and gut feelings are not enough to risk design mods when public safety could be compromised.

Len Mason in the Minnie book said to test the finished boiler to 120 psi and hold it there for some time. In a previous sentence he said model boilers should be tested to twice working pressure, so I infer he intended working pressure to be 60 psi. Looking at the small area of the throat plate, its' flanged sides, the fact that the top butts against the boiler tube to support it against forces induced by pressure, and that the throat plate has 6 stays, even at 120 psi the stress on the plate and stays is very low. If the joint is silver soldered competently I would not expect any trouble.

Answering an earlier comment re number of Minnie boiler failures, I have never heard of one or read of one failing, for the 40 year period of my model engineering interest. Many have been successfully made and run. I would be interested to hear if there are any failures and how they failed.

[JasonBModerator @jasonb]

Minnie is only 50psi WP so not too stressed.

[Phil H1Participant @philh196021]

I think we are also in danger of wandering off trail a bit aren't we. The point is Mark is doing a great job so far – looks nice.

[Paul KempParticipant @paulkemp46892]

Posted by Phil H1 on 15/08/2020 19:18:47:

I think we are also in danger of wandering off trail a bit aren't we. The point is Mark is doing a great job so far – looks nice.

Agreed on both points. Mark is making a great job of it and shouldn't be concerned by the doubts that were expressed.

Paul.

[Bob WorsleyParticipant @bobworsley31976]

Anyone building any model from plans gets a collection of sheets of paper, no calculations to be seen about boiler safety. In fact my Thetford Town drawings assume you are going to rivet it, with brazing as a last option if it leaks.

If a line contact joint is considered to be perfectly ok, then why not line joint all the other joints? I would guess that certainly wouldn't be acceptable to any inspector. Why not? It is how a steel boiler is made, never flange them. So there must be a fundamental difference between silver soldering and arc welding. One is done by a trained professional?

There was a comment in an old ME about where do all the models made go to? Must be tens of thousands. And since the boiler is the first thing made with a traction engine, how many are made, leak, and the person gives up, 50%? How many Minnie boiler kits have Reeves sold over the last 50 years?

And yes, the boiler does look good, well done. It amazes me just how well the pickle cleans the copper, lovely.

And yes, again, these are my opinions.

[JasonBModerator @jasonb]

Bob can I suggest you start another thread or tack your latest post onto the joint gap one rather than derail Mark's thread even further.

EDIT I've moved it to your Flange thread here

Edited By JasonB on 16/08/2020 13:37:11

[Mark BParticipant @markb43031]

Well I'm happy to report that I have had positive feedback from my fist boiler inspection. It mostly involved looking at my joints and confirming I'd used the correct thickness of copper and generally looking at the design.

No issues so far. The next stage is to silver solder the boiler tubes into the firebox assy where it needs to be inspected again before they disappear into the boiler.

I'll probably have a go at this shortly so will post some more pictures of the progress.

[Paul KempParticipant @paulkemp46892]

Mark,

Sounds like you are well on track, previous pictures look really good.

Probably worth emphasising that as you have followed the proper route and involved your inspector from the outset you should be assured of an excellent result and others would be well advised to follow your example. The boiler inspector should be your friend not your foe.

Look forward to more pictures as you progress.

Paul.

[Mark BParticipant @markb43031]

A little more progress, this time with the addition of the firebox crown stays and some boiler tubes. It was a bit fiddly aligning the boiler tubes.

[Jeff DaymanParticipant @jeffdayman43397]

Looks good Mark! well done. May need a bit more silver solder on the firebox wrapper as seen in middle picture, looks like a small void. May not be an issue but just mentioning it as I noticed it. Could be the wrapper to flange gap was a bit too wide just there.

[nigel jones 5Participant @nigeljones5]

Mark, well done but some words of caution from someone who does this for a living.The solder hasnt flowed correctly on some of the tube joints, possibley burned out flux or more likely just not enough heat, also the top rivet looks like it hasnt been soldered (might just be the light). Before proceeding with the build I strongly advise you to re-flux the tubes and re-heat until it all flows smoothly. If you have even the slightest problem in this area it is near impossible to correct once fully assembled and soldered and then the whole boiler is scrap. Any lumpy bits of solder indicate potential problems. Picture two shows two perfect joints and two not perfect joints, they all need to look like the smooth ones or they are likely to leak.

To answer Bob, you cannot easily compare the process of arc welding to soldering. One relies on a filler metal finding its way into a gap by capiliary action (dont get me started on gaps!) and the other deposits liquid metal onto the surface, gap or no gap. In reality a boiler constructed entirely without any flanging and competently silver soldered would be just as strong as a similatly welded boiler. Flanging originated in the days when boilers were riveted together and then cailked with soft solder plus its difficult to hold a boiler together without any flanging but it has been tried and done by the Australian federation whilst they were investigating this very notion. All their joints passed.

[Mark BParticipant @markb43031]

I've reinspected the tubes and decided that a refluxing and reheat wouldn't harm. I agree this part would be a challenge to rectify later on. It's going back to the boiler inspector on Wednesday so it will be closely examined then.

Reheating again has improved the look of the joints and minor lumpy solder turned unto a puddle. I've also photographed it from the inside which I think looks okay now.

[nigel jones 5Participant @nigeljones5]

Now thats a massive improvment, well done indeed. I almost deleted my words as I thought they would be taken the wrong way but im glad they werent…..the way the solder has run on the inside is a sure indicator that it was at the correct temperature and all should be good.

[Paul KempParticipant @paulkemp46892]

Very nice. I was thinking the same as fizzy but he was braver! I couldn't come up with the right words to post a suggestion! That looks to have flowed very well, your inspector should be very happy with that.

Paul.

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