5" gauge Britannia (a builder's diary)

[westlin]

Steve

Aware the 5" drawings use girders on top of the firebox, any reason you did not opt for using stays. Ive just finished a 3 1/2 brit boiler and getting the solder to the back of the girders was challenge.

Regardless great progress and quickly as well.

Stephen

[uuu]

Probably for the same reason you "opted" to use girders?

Wilf

[springcrocus]

There's not much progress on the boiler front at present, the outer girder stays are giving me some grief and, in order to deflect a load of smart-arse comments, I will not write it up until I'm 100% satisfied with the outcome.

The drawings show that the dome bush is optional on Britannia because the regulator is in the smokebox. I was going to omit the dome bush but John the Pump suggested that it would be useful as a means of flushing out the boiler - nice, big hole - and it could do the additional duty of supporting the steam collector pipe instead of adding another small hole in the boiler shell further along.

There are no dimensions given for the bush, just an outline on the drawing of the shell so I scaled from this instead, then modified to suit my needs. The bush and it's cover plate were made from bronze offcuts starting with the bush. A hole saw was used to remove the centre and a parting tool modified to trepan the outer size.



I try not to waste bronze unneccessarily and these are the outcome.



The turning of the bush was quite straightforward and the component was then set up on the mill to drill and tap eight 4BA blind holes for the cover plate. I chose a 2" PCD so the hole positions were simply "1.0, 0.0" and "0.707, 0.707" respectively.



The cover plate was machined from a weirdly-shaped offcut of bronze using the four-jaw chuck. The old wheel bearing came in handy for extending the centre to provide support against the intermittent cut.



The packing pieces between the jaws and the workpiece were to create enough room for the turning tool to function without clouting the jaws.



Second op. was undertaken using soft jaws, bringing the flange thickness to size and maching the spigot for a good fit in the the bore of the dome bush. Then it was drilled on the mill - same settings as the dome bush - and finally returned to the lathe to be faced to length.



I've stopped at this point as I haven't yet decided whether to use a gasket or an O-ring for sealing, it will get pretty hot here.



Steve

[JonL]

I wondered about putting some sort of support in there for mine (3.5) too, the pipe does seem a little lost in space.

[kipford]

Steve
I understand your wish to avoid the 'smart arse' comments, but can you include the issues you have met in final write up please. My Aspinall boiler has girder stays and any info about what/what not to do, warts and all would be interesting.
Dave

[springcrocus]

Aug 30, 2019 12:57:58 GMT kipford said:

Steve
I understand your wish to avoid the 'smart arse' comments, but can you include the issues you have met in final write up please. My Aspinall boiler has girder stays and any info about what/what not to do, warts and all would be interesting.
Dave

Yes, of course, Dave. Once we have a satisfactory solution then "I told you so..." comments, which is what I'm trying to avoid, count for nothing. My colleague and I have just had a good session in the workshop and when it comes out of the pickle, I will be able to see if we have been successful. Then I will describe this whole section of the journey.

Regards, Steve

[springcrocus]

As I mentioned in a previous post, fixing the outer girders was a bit of a challenge. I'm afraid the photographic record is a bit sparse here but I will try to describe the problems I encountered. It all started because I should have left the backplate till last. The inner girder soldered up fine because the top of the firebox was pretty flat and it was easy to get good contact with the fabicated girder along most of it's length. The outer girders sit on the curvature of the firebox and it was much harder to get metal-to-metal all the way along. Here's a reminder of the layout.



Following the advice of using loose rivets, I set the firebox up in the hearth tipped over to about thirty degrees and laid solder on the the top of the join on the upper one and in the gulley of the lower one. Heat was applied from below each component until the solder melted and wicked down into the joint.



However, I didn't bend the rivets over enough and the top one lifted a little at the end and I wasn't happy with the joint. The lower one was better but I should have used more solder and daylight could be seen in a couple of places under both girders. I decided to revisit both joints and started with a really good clean up and pickle to try and get everything scrupulously clean. After tapping down the wider gaps the assembly was fluxed up again but the existing solder got in the way of getting the ends down tighter.

At this point, I need to explain how I light the area. When annealing, I turn the lights out and judge the temperature of the material by watching the colour. However, during soldering and particularly when using solder laid into joint gaps, I found it difficult to see when the solder had fully melted due to the red glare of the copper and the brightness of the flame. A couple of times I have found bits of partially-melted solder around joints. Now I flood the area with 6000K LED lighting and this completely swamps the colour generated by the heating and this allows me to see perfectly clearly when the solder starts to melt and I can chase it along from underneath with the flame.

During the second heat-up, I noticed that I was putting in more heat than before and that the solder under the girder was starting to re-melt but, more importantly, the solder around the top corner of the backplate was starting to go semi-liquid and I backed off straight away. After cooling, cleaning and pickling, I could see that the heat had also lifted the central girder slightly away from the top of the box at the back and, by now I was wary of another cook-up in case I made matters even worse.

I decided to drill and tap four new holes, one in each girder at the firehole end, and some sloppy 4BA bronze screws were made. These were fluxed, then screwed down touch-tight and the whole assembly fully fluxed up again.



Rings of solder were placed around the screwheads and solder laid in the gulleys as before, including some in the centre girder and on top of it. Then my colleague and I applied heat from both torches, one of us concentrating on the top part and one on the lower. Once we were up to melt temperature, one torch was removed and the other used alone to draw the solder down into the joint.



We were in better control of things this time compared to when I went it alone and we now have solder along all the joins with no daylight showing. This is the lower girder but the others are similar.



If I was doing this job again, I would either fix the girders before fitting the backplate, or use bronze or copper screws to hold them in place instead of rivets.

This has been a frustrating but highly instructive lesson for us both - we are both novices at silver-soldering but we have learnt quite a lot along the way. Many of you will have been doing this for years and wondering what all the fuss is about but, unless you get the opportunity to work along side an experienced person, the best way to learn anything is get stuck in and get it wrong. I've always learnt more from my mistakes than from my successes and I hope this offers encouragement to some of you.

Steve

[kipford]

Steve
Very informative, a lot of food for thought here.
Dave

[Roger]

That's a great result Steve, I very much like the idea of the flood lighting. I struggle with seeing the puddle when tig welding and find a small LED light helped a bit. Knowing what you've found, I might try a much brighter one to see if it's even better.

I probably went over the top with phosphor bronze screws holding things together, it certainly takes a lot of time and effort adding them all. Stopping things from moving when hot isn't easy. I'm not convinced that screws need to be a sloppy fit. Maybe that was true in the days of Silver Solder with Cadmium filler, but I really don't think you'll stop the Solder penetrating the joint however hard you try with the current stuff that flows like water.
I made my stays a lose threaded fit, and it just means it's harder to fill the gaps in the threads and you use way more solder. I wouldn't do that again.

[springcrocus]

Sept 5, 2019 8:18:25 GMT Roger said:

... I'm not convinced that screws need to be a sloppy fit. Maybe that was true in the days of Silver Solder with Cadmium filler, but I really don't think you'll stop the Solder penetrating the joint however hard you try with the current stuff that flows like water.

Roger, I agree with you on this, a lot of my problem has been because of the poor fit of the girders to the firebox top. Sometimes the solder has just pissed straight through the joint and out the other side, wetting the metal but not forming a decent fillet. We are getting the hang of it now, though. Preparation is everything.

Regards, Steve

[jma1009]

Hi Steve,

From your pics and sketch, I would say you did the bottom of the girder stays in a novel way, with the inner firehole door backplate in position already silver soldered, and heating from the outside.

I am very impressed with the result, and when I do my next boiler I might even adopt your approach, though I will leave off the inner firehole door backplate.

The problems with getting a good fit of the girder stays to the inner firebox applies equally to other methods of silver soldering up - if you can get the tip of a 2 thou feeler gauge in with a bit of a push then you are OK, but the tip of a 4 thou feeler gauge going in is too much of a gap. You can't rush getting these joints correct, and assume 'S-d it' I'm not going to worry about the odd bigger gap in places.

I've never done girder stays to the firebox inner wrapper without a re-heat and re-silver soldering, so I think you have done very well.

Cheers,

Julian

[twombo]

Steve, I really Iike the 6k lighting tip! My vision in such things has been a struggle! If I may ask, what type and thickness Silver alloy are you using? I have a legal source for Cadmium bearing. Is it a good move as a beginner to use this? Both 24% and 55% are available. I suppose The usual step braising method?

Thanks! I really, kind dread, the girder stays! Time will tell!

Your build is Very informative. Great work!

Your dome bush report really answers a lot of my own concerns. Using a hole saw to remove excess material is a great idea! Might that center plug be useful fn the steam dome, itself?

Roger,
the only time i see the puddle whilst TIG welding is when the tungsten plunges INTO the puddle! Nice greenish flash! Reminds me of the green flash in the exhaust of the SR 71 engine upon ignition! Really pretty at nite!

Mick

[92220]

Very nice job Steve! Good lighting is definitely a great help when silversoldering, I've found too. I have a 300w halogen security flood light about 5' above the hearth. It does make working there a whole lot easier!!

Bob.

[runner42]

Hi Steve,

your tenacity to get it right is commendable, I think you need the same approach, even more so when dealing with soldering the girder stays to the outer wrapper. Getting a good solder joint and seeing that it has been achieved is more challenging. Girder stays are not a feature of the Australian boiler code for this reason.

Brian 

[springcrocus]

Mick, for that we used 1.5mm rods 55% solder and EF flux. I'm a beginner, too, so cant answer the other part of your question.

Julian, thanks for the tip about feeler gauges. This was put into practice this afternoon.

Bob, it's the blue-whiteness of the 6000K LED which swamps the generated light. The copper just looks the normal pinkish colour at solder-melt temperature. The old floury light never did the same.

Brian, the drawing shows the stays bolted at the top, not soldered, so that is what they will be. You will see when I get there.

Thanks to all for the compliments and encouragment.

Regards, Steve

[springcrocus]

When the time came to join the tube assembly to the firebox inner, the front of the combustion chamber was manipulated until it was a snug fit inside the rear tube plate flange. This mostly involved flaring the edges of the chamber outwards, effectively stretching the metal a little, and letting the tube plate force the combustion chamber back to shape.

Prior to setting up in the hearth, Wilf suggested that we make a strap to hold the two parts together and set the angle of the tubes correctly. On the drawing a line was projected forward from the underside of the girders to the front of the tubeplate and the distance from this line to the outside of the front tubeplate measured.



A length of 8mm x 40mm flat steel was cut to length, a spacing piece drilled and then welded on. This was then lightly clamped to the inside of the girder stays and bolted to the front tube plate with a spacer between to set the correct distance, allowing for the thickness of the strap. The overall length was checked and the girder clamps tightened up.



The whole assembly was then set up in the hearth, well-fluxed and with 1.5mm dia 55% solder sitting on the rim. 2mm dia would have been better but I have none.



Working both sides, and careful not to set each other alight, we heated the underside edge of the combustion chamber tubeplate, chasing the melt around the top. Because we were close to the girder stays, we refluxed those joints as well, just in case they started to soften and also the tube ends nearest the edge.



Once the resting solder had melted, we added extra solder by hand until we could see a good, filled joint all round. After cleaning and pickling, this is the result. The tubes are fine because we used high-temp 38% solder for those and the reheat has not disturbed them at all.





When I originally soldered the tubes to the tubeplate first, some felt that this was not the right way to go but I think they forgot about the depth of the combustion chamber. Although the photos are taken with the backplate in situ, it still shows how difficult it would be to solder the tubes to the tubeplate after it is in situ. The first picture is through the firehole.



It's a long way down.



I hope I have shown that it is perfectly possible to solder the tubes first and the plate second when there is a deep combustion chamber involved. However, a more traditional boiler is probably better constructed in the manner described by Julian and Brian.

Steve

[springcrocus]

It's not a pressure test by any stretch of the imagination but at 5pm on Friday I plugged the ends of the tubes, upended the assembly in a bucket and filled the firebox with water up to the lip of the front throat plate.



Eighteen hours later the bucket is dry and the water level has remained constant.



So, no gaping holes anywhere and very encouraging.

Steve

[Midland]

Nothing like a bit of success to cheer us up. Good to see your accomplishment, and of course jealous (nicely) too!
D

[timo]

Steve,

That is going really well, you must be chuffed (pun intended).

Tim

[twombo]

Steve, This is getting exciting! Thank You for the education!

Mick