5" gauge Britannia (a builder's diary)

[springcrocus]

The next thing I did wrong was the firebox wrapper, if that's the correct term for it. The development outline of the inner firebox was marked out using a paper template that I created by wrapping it around the wooden former.



The waste was then removed with a jigsaw, the plastic protection peeled off and the workpiece annealed. I used a bigger torch this time and got the copper up to red heat in about three or four minutes.



It needed two more reheats before I was able to reach this stage...



... and then it was a case of easing the combustion chamber to final shape for a snug fit inside the tubeplate.



The throatplate will be made next so that the firebox can be fitted to the shape. However, there is a problem here that I will explain later.

Steve

[springcrocus]

The combustion chamber throat plate was made next and, because I'm making this boiler exactly to drawing, I didn't modify it to my own version of a double flanged throat plate. After marking out, cutting and annealing, the plate was flanged around the former to produce the basic shape. There is a reverse bend here and I made sure the material was good and malleable to accomodate this.



Next, the shape of the combustion chamber was marked onto the plate ...



... and a new circle drawn inside this to allow for the flange. The waste was then removed using a jigsaw.



The next part was easing the flange to the shape of the barrel and this took ages, nibbling a little away, bending, annealing etc. The compound circular shape was not easy to form and I took most of the afternoon on this.



This is the final shape although it will still need melding to the inner firebox prior to soldering.



And it's a good job that I didn't make this adjustment because I made a mistake with the firebox wrapper. I will explain this at a later time but, for now, the flanged throatplate saved the day. However, the plan was always to make the flange, and the boiler inspector agreed. A far more satisfactory joint than the butt joint shown on the drawing.

One last picture to show the firebox temporarily sitting on the tubeplate with the throatplate in position. And that's a three-foot rule stood up against it.



Brian, if you fancy soldering those flue tubes down the bottom of the combustion chamber, all I can say is, "Good luck with that, mate".

Thanks for reading,

Steve

[delaplume]

Hello Steve,

Well, that has all the hallmarks of a good, workman-like job and no mistake !!.........I totally agree re}-- that throatplate flange as it not only gives additional strength but can help in location as well.....How the original design got away with a butt joint I'll never know.......Looking at your drawings took me back to when I designed my "Bear" boiler as there is a lot of similarity there, allbeit with a 50 year gap between them on the full size...

Yes, BIG aren't they ??........and as the final assembly gets nearer so the quantity of gas consumed and silver solder sticks required increases almost exponentially ( and thus these things as well----> £££££ )...and that's not yet allowing for labour costs either !!

Keep up the good work !!

Alan

[jma1009]

Hi Steve,

"Brian, if you fancy soldering those flue tubes down the bottom of the combustion chamber, all I can say is, "Good luck with that, mate"."

That was a very cheap jibe on your part Steve, against me plus Brian who has already completed successfully one complicated boiler - a belpaire firebox and tapered barrel type. Actually it is not too difficult to do once the combustion chamber is silver soldered up with its wrapper, though I would first do the outer boiler shell and throatplate first.

I was expecting this evening to see your tubes all silver soldered to your combustion inner firebox tubeplate as you stated you would do!

Anyway glad to see some of the discussion has been absorbed, and you have refrained for the time being to do this.

Cheers,

Julian

[springcrocus]

I can feel a head of steam rising, and the boiler isn't even built yet.

Steve

[ettingtonliam]

And just when I was enjoying reading about Steve building his boiler.

[JonL]

I think on the 3.5 gauge Brit (which as stated many times before is notoriously hard to get the throatplate right) the original words and music call for Siffbronze brazing. I plan to use a flanged one as you have.

Keep it coming Steve, very interesting and educational.

[springcrocus]

Before I started building the Britannia boiler, I obviously did some research on the internet and one of the things I came across quite early was a set of pictures from Station Road Steam showing a set of formers and a collection of cut plates that they had for sale way back in 2007. I promptly downloaded these pictures and have used them as a casual reference since.

Here's the link

By the way, Station Road Steam often get spoken about, and their material linked to, but you don't normally see much in the way of thanks for keeping their archive of pictures going over such a long time. So many thanks, guys, for providing such a valuable resource, and I hope you keep the archive going for another twenty years so us amateurs have some reference material to turn to and help us along.

In this instance, however, the person who cut the plates made a mistake with the firebox wrapper, specifically the cut line from the base up to the combustion chamber. Because the front of the firebox slopes up and forwards, the combustion chamber needs more material at the bottom than the top. A couple of sketches show more clearly what I'm referring to.





The last two pictures show where I projected the point of the lowest, rearmost part of the combustion chamber to produce a cut line. It also produces the wrong angle at the front.
The next two pictures show where it should have been. Points A - A are created from the angled front throatplate up to the centreline of the boiler.





I fell into the same trap that the other person did but, in my case, because I chose to make a flanged throatplate this covered the gap that would have been left if I has made the butt-join throatplate instead. I hope this information is useful to anyone else making a 5" Britannia boiler.

Steve

[JonL]

Seconded for SRS, I use their photos all the time for reference, and the data has been useful for the Wiki.

I like the use of paper scraps, nice to know I'm not the only one who isn't on to CAD yet!

[springcrocus]

I've been having problems working with this high-temperature silver-solder, trying to get the heat into such a large mass of copper and, more importantly, keeping it there! Still, I think I've finally got the hang of it and might have something to photograph when it comes out of the pickle.

I've even had a collegue giving me assistance but it's still difficult to get to temperature with propane alone and I might see if I can borrow another collegue's oxy-propane set instead. The 55 percent silver solder should be a doddle after this.

Added to all that, I almost burnt the workshop down the other day, which was quite exciting. Destroying a set of six-tread fiberglass steps was a sharp reminder about the danger of spraying flames willy-nilly about the place and not keeping one's eye on the ball. Lesson learnt, and a bit more care needed when playing with fire!

Regards, Steve

[Roger]

If you can go down the Oxy-Propane route, 55% is all you will need for sure. You'll still need a big Propane torch to get it all smoking hot before using that though, and re-heat it after a few minutes.

[delaplume]

Hi Steve,

Oh dear---sounds like you've been busy (in more ways than one )....However I'm glad to see you're OK after the recent "Flambe' " escapade....That Glass Fibre is nasty stuff when it gets going !!..........Fumes etc..

Yes, that's a good idea having another person involved, if only to be an extra pair of eyes ( for advanced warning of danger ) and a second pair of hands in general......PLUS a second point of view on procedure etc is always welcome I'd have thought ??

Adding Oxygen will ramp-up the combustion Temp. and is ideal as your second torch for close-in detail work--- but carefully done..

Tip}--- Remember to pack firebrick around the whole height of the assembly ---- usually full-sized blocks, one on top of the other and formed into a vertical 90 degree Vee shape.....And also to pack loose brick into any internal open spaces eg}--- the firebox / combustion chamber...

Over 30 years ago now I had a "Customer" who thought that the gas came free of charge !!!

Onwards and upwards !!

Alan

[David]

As Roger says. My mogul boiler is probably a lot smaller than the one you're building and we still used a large propane torch to get the heat in to begin with and sometimes kept that going for general heat while using an oxy/propane torch to do the soldering. The oxy/propane is excellent, even for smaller jobs in steel etc.

In my case there was no hearth, only some firebricks to sit the boiler on. That probably didn't help.

[Roger]

Jul 15, 2019 9:13:36 GMT David said:

As Roger says. My mogul boiler is probably a lot smaller than the one you're building and we still used a large propane torch to get the heat in to begin with and sometimes kept that going for general heat while using an oxy/propane torch to do the soldering. The oxy/propane is excellent, even for smaller jobs in steel etc.

In my case there was no hearth, only some firebricks to sit the boiler on. That probably didn't help.

I don't think you need a hearth, just something that won't catch fire while you're heating the boiler. These things are only necessary when you don't have the benefit of the more intense heat of an Oxy torch and there's no way you'll get it hot enough unless you try to retain as much heat as possible. We just laid a fire blanket over the boiler after pre-heating. That kept enough heat in for several minutes.

[springcrocus]

I have had to make a few changes to the firebox wrapper because of my mistake with the cut-line of the combustion chamber. The throatplate has to come forward at the top but it will still leave the angle a little too upright. This won't matter, however, it just increases the water space at the top of the plate, but it did require a strap around the underside of the combustion chamber. The soldering has been done in stages with 38 percent silver solder, the joining strap first, followed by the packing strap. Next, the throatplate was held in place with four copper rivets and the first side soldered. These are the only two photos I've taken of this part of the build.





The heat was applied to the inside of the box and the solder was rested on the outside of the box and covered with HT5 flux. My soldering won't win any beauty prizes but at least I can see that full penetration has occurred and I'm happy with the joint. This was soldered with propane only. The end of the strap and the filler piece will be dressed back later and the other side will be done tomorrow.

I have checked and the changes do not fall foul of the boiler regulations but the boiler inspector will see it this weekend anyway. The additional material acts as strengthening rather than weakening as long as the solder join between the layers is satisfactory. This will obviously be confirmed or rejected at pressure-test time.

Steve

[simplyloco]

Jul 15, 2019 21:41:53 GMT springcrocus said:

I have had to make a few changes to the firebox wrapper because of my mistake with the cut-line of the combustion chamber. 
SNIP
I have checked and the changes do not fall foul of the boiler regulations but the boiler inspector will see it this weekend anyway. The additional material acts as strengthening rather than weakening as long as the solder join between the layers is satisfactory. This will obviously be confirmed or rejected at pressure-test time.

Steve

I wish that I had done something similar: I would be about £1400 richer!
John

[jma1009]

Far too parsimonious (stingy) with the silver solder, and the rivets are not silver silver soldered so far as I can see.

This is an internal assembly that will get re-heated numerous times when doing the crown stays, and the tubes, and the staying.

Cannot see any silver solder penetration between the additional piece added on the inside pic 2.

There is an inch or so length of the flange to combustion chamber wrapper showing no silver penetration on the right hand side inner pic 2, and nothing at all on the outside pic of the lefthand side on pic 1.

Have a look at my Stepney boiler build when I used the high melting point ductile grade on the throatplate joint to barrel joint, and Roger's Speedy boiler build, and Paul Tompkins' pic's to Pete for Doncaster as to how these bits should look after silver soldering.

Just commenting on what I see from your 2 pics.

A riveted joint ought to be got right first time with silver soldering as the un-silver soldered areas get an oxide layer that might or might not get the oxide layer removed on a re-heat to do these again properly. Anyone who has scrubbed a copper boiler after silver soldering and removing from sulphuric acid will know what I am getting at. C106 is not as bad as C101, but it is still a mighty problem on a flange joint.

I commented on Pete's Doncaster boiler build how pleased I was to see generous use of silver solder... that is only a month ago! Pete's Doncaster boiler has generous silver soldering.

I still think you are doing everything in the wrong order by not doing the outer boiler first and outer throatplate to same first and at the same time the outer firebox wrapper.

Cheers,

Julian

[simplyloco]

Jul 15, 2019 22:24:54 GMT jma1009 said:

Far too parsimonious (stingy) with the silver solder, and the rivets are not silver silver soldered so far as I can see.
SNIP
I still think you are doing everything in the wrong order by not doing the outer boiler first and outer throatplate to same first and at the same time the outer firebox wrapper.
Cheers,
Julian

diary[ dahy-uh-ree 
noun, plural di·a·ries.
a daily record, usually private, especially of the writer's own experiences, observations, feelings, attitudes, etc.


Steve has already indicated that this is a diary, not an opportunity for other (lesser?) mortals to criticise...
Cheers!
John

[jma1009]

Hi John,

Yes, I gather this, but surely you would not want Steve to take your £1,400 'hit'? Neither would I, nor would I wish anyone else to have problems with their own build boiler, in the same way I would not want any disasters with any of my own boilers over the years.

Steve has already altered his original silver soldering plan of silver soldering up the tubes to the combustion tubeplate first, as stated on here 2 weeks ago.

It is a huge boiler in 5"g and also very complicated with the tapered barrel, combustion chamber, and belpaire firebox. It isn't far off Pete's Doncaster boiler and more akin to 'delaplume's (Alan Redgrave) The Great Bear boiler, both who got commercial boiler makers to make their's. You got your own second 3.5"g Brit boiler built commercially too.

If Steve has a closed mind to comment then that is his right - just let him state very clearly this is a closed thread for others and only he himself is going to post.

Cheers,

Julian

[delaplume]

Hello everyone,

The difference between my Bear boiler and the others is that I designed it myself and also created a set of Master and working drawings from which Jon Ellis manufactured it.............In keeping with the spirit of Old Style methods I even purchased a fully counterbalanced drawing "Engine" along with plastic squares, French curves, erasure rubbers etc and an assortment of 2H and HB pencils.......I also tried using my old Admiralty issued Slide Rule-- but had forgotten how to so the electronic calculator was pressed into service...

I also came across this same problem of yours at the combustion chamber and if I remember correctly it took me several re-draughts before we ( John and myself ) were happy with the final version...

.Don't forget that the tube "nest" will rise by approx. 5/16" from the firebox tubeplate to the smokebox tubeplate in order to help create an artificial draught.....

Best regards

Alan