5" gauge Britannia (a builder's diary)

[springcrocus]

The backplate for the firebox inner is one of the smallest pieces coming in at a mere 188mm x 160mm. It was duly marked out around the former like all the others.



Same procedures as before and this is the finished backplate.



The firehole ring gets soldered into this before the backplate is assembled and that was made next. The drawing shows a piece of 14swg tube wrapped with a 10swg ring and, luckily, I had a suitable piece of 2" OD tube in stock for the inner. To create the outer, I calculated the circumference and milled up a piece of copper to suit.



After bending, and finding it too short, a new piece was made 3/16" longer. I've obviously forgotten how to calculate.



This was annealed before wrapping around the tube. Then the ends were soldered together in the vice with medium-temperature (38%) silver solder.



Finally, the two parts were lined up and a pair of 3/32" holes drilled and copper pins fitted to keep the rings in place. Then they were soldered together before turning both ends to length in the lathe. One tip to offer others: don't try and turn the thin-walled copper tube in a 3-jaw chuck without some additional support. I distorted my first piece of tube and had to bin it. After the ring was soldered on, it was much more rigid.

Finally, the firehole ring was squashed to shape in the vice...



... and the shape marked onto the backplate. The hole was stitch-drilled freehand with a 3mm PCB drill.



This time, I just chiselled out the waste piece and filed to size.



Before soldering the firehole ring into place, I secured the backplate to the firebox and drilled four rivet holes, two each side, for holding in place during soldering. Because of the angled back, the backplate wants to keep falling inwards to the firebox and the packer clamped to the crown stops this happening.



Finally, the firehole ring was soldered into place. Now the backplate will be joined to the inner firebox to complete this stage of the work.



Steve

[delaplume]

Hi Steve,

That Copper is a nice pink------what pickle are you using ??

I'm not familiar in detail with this boiler design so where are the blowdown valve bushes being fitted ??

Thanks for keeping the photo size realistic and not swamping the screen....much appreciated.

Alan

[GWR 101]

Nice work Steve, have been following your progress with great interest. Regards Paul

[runner42]

Hi Steve,

I have been reluctant to add my voice due to my previous comment that may have put you offside, but I am compelled by your progress in boiler making to say that you have embraced the art/skill with the same workmanlike approach that you have displayed in the machining phase of your locomotive build. You have demonstrated that there is no absolute way of tackling the task and that the best approach is one that the builder is comfortable with with the facilities that he has to hand. You have made the reporting even more interesting by a warts and all approach, which is gratifying to those builders like myself that doesn't always get it right first time.

Brian 

[springcrocus]

Thank you, Brian, that's pretty much what I've been saying all along. There are a hundred and one ways to do most jobs and if the one you choose is the one that works for you, then it's one of the hundred and one right ways of doing it.

Just a quick update on the backplate today. My colleague visited yesterday and we were able to get two burners working on the inner firebox, working one side each and letting the heat flow round to the back. The firebox is set up with its firehole resting on a couple of blocks to get the heat in from below and the solder has been preformed and rested on the edge of the backplate inside.



Flux was laid around the pre-solderded firehole and also over the rivets, inside and outside. As many blocks as possible were laid around and over the top as we could get without impeding the torches. After a good clean-up, this is the final result.



More on the front throatplate next.

Steve

[simplyloco]

I don't think that you could better that result!
John

[timo]

Steve,

That boiler is looking as near 'professional' as I can tell.

You should be very proud of what you are achieving.

I look forward to seeing it in the flesh - will be up at Broadfields on the next members day all being well.

Tim

[ettingtonliam]

A lot neater than I can manage.

[philh1aa]

Steve,

Some nice joints and it is nice to see a boiler build thread. Please can you say what % of silver you used for installing the firebox backplate? Also, are you planning to silver solder the side stays in position because I notice that other descriptions leave the backhead out until the side stays have been soldered in place.

Phil H

[springcrocus]

Phil H - that was done with 55% silver, it's a big, wide join. The other query, just wait till I get there.

The front throat plate was clamped to the mill bed and the side flanges reduced to just over a half-inch high.



Julian commented that butt-joining the front plate to the boiler barrel needed especial care and I had already decided that I didn't like the method shown on the drawing. I decided, therefore, to make some form of collar to butt the front plate up to and three pieces of copper were milled to 1/4" wide and shaped to fit around the barrel.



The front plate was placed on the barrel and adjusted until the various lengths agreed with the drawing and a pencil line drawn around the periphery. The strips were then lightly clamped to the barrel, pushed and shoved till they matched the drawn lines, then clamped tight. 3/32" holes were drilled at various positions and rivets temporarily fitted to hold the straps.



Once happy with the position, the rivets were reversed (heads inside) and hammered flat into countersinks on the outside. There is loads of space under the cleading and these straps will not interfere with the fit. In fact, they will help.



If you spotted the white dots on the straps, these are a series of 8BA holes that I have drilled through the straps and will be available for fitting studs to after soldering. Whether I use them or not remains to be seen but it's easy to make provision now rather than trying to drill and tap some blind holes later. Here is the barrel after soldering which we did on Friday and the tippex has stopped the solder entering the holes. Thanks to Roger for that tip.



After cleaning up and filing down any surplus solder, the throat plate was fitted onto the barrel and gently tapped around until it butted nicely up against the strap.



Finally, the inside of the barrel was peened outward until it slightly flared over the throat plate and trapped the barrel in place. Prior to fitting, I also drilled the hole for the blowdown bush.



This assembly is now mechanically sound and will be soldered in due course. The greatest gain here is the fact that there are now two faces for the solder to join, the vertical and the horizontal, and will result in a far stronger join. And I get somewhere to fix the cleading for free, if I choose to use it.

I said I had a plan but it might not suit others. I don't think I have the skill to try and form a double flange on a plate with a thirty degree bend in it, and I'm certainly not going to waste a load of time trying to find out. I wish good fortune to anyone who wants to have a go.

Steve

[timo]

Steve,

A really neat plan. The boiler is really coming together.

Tim

[ettingtonliam]

My Locomotion boiler has a similar joint to your Brittania barrel/throatplate joint, where the cylindrical firebox passes through the boiler backhead, projecting about 3/4" beyond its outer face.
It isn't exactly a butt joint is it, that would be the barrel butted up to the throatplate, with the joint in tension rather than passing through it with the joint in shear. I think mine would be OK, its only for 60 psi working pressure, but I had considered adding a 1/4" wide copper band around the joint on the outside of the backhead, silver soldered to both the firebox and the backhead, just about doubling the area of soldered joint.
Having seen you do yours, thats convinced me to do mine that way too, its very little extra work. I know it deviates from the published drawing but I can't see my boiler inspector raising objections when I mention it to him - without doubt its a stronger joint.

[jma1009]

To my simple mind, a but joint up to a but joint is a but joint. A flanged plate is something different.

Get those rivets silver soldered!

I had the first joint on my Railmotor boiler rejected by Arthur Grimmett and John DeBank (barrel to firebox outer wrapper and throatplate) because I had missed the rivets.

I was 17 years old at the time, and using John Debank's old 5 pint paraffin blow lamp. I was following Don Young's description in ME of how to do the Railmotor No.1 boiler with no mention of silver soldering rivets used in securing the bits together.

The whole boiler was done in Easyflo 2. Never had a problem reheating to do those pesky rivet heads, but I was using Thessco F flux, as I have always used.

Cheers,

Julian

[philh1aa]

Julian/ all,

I am always unsure about rivets for boiler work because if you peen the head to make them reasonably tight, the solder is only likely to surround both sides of the head without full penetration down the sides/ hole of the rivet?? I have also seen people suggesting that you fit the rivet and perhaps just bend the shank. That would then hold the parts loosely in place but allow solder to enter the hole. Is that the best approach?

Phil H

[jma1009]

Hi Phil,

The last 2 boilers I've made I bend the shank of the rivet, and fit the rivets 'loosely' with an application of Thessco F flux.

You cannot get a rivet with silver solder penetration if it is hammered home tight. I also try and use as few rivets as possible.

Hope this makes sense.

Water leaking around un-silver soldered rivets on a boiler on an hydraulic test is not an edifying prospect, and I was rightly taken to task over this when I did my first boiler with the first braze up of 3 joints at the same time.

Cheers,

Julian

[philh1aa]

Julian,

Thanks, yes it makes perfect sense.

Phil H

[92220]

Lovely job Steve.

As Julian says, progressive silver soldering (multiple heatings) is not generally a problem. I've silversoldered the same fabrication many times with no problem. My cab floor base is made up of 32 separate pieces of 1mm mild steel sheet, and most joints were soldered individually, with oxy propane torch and a No.3 nozzle. Silver solder, once melted and then solidified, has a higher melting temperature than when first melted. I think I read on the Johnson Matthey site that it goes up 25C wehen melted and solidified. I have silversoldered right up to a previously soldered joint and fused the 2 together with no problem. The original joint stayed solid up to about 1/4" from the liquid silversolder. Just don't keep the flame there too long otherwise the original can get up to it's higher melting temp.

Bob.

[springcrocus]

Aug 7, 2019 22:37:29 GMT jma1009 said:

Get those rivets silver soldered!

Cheers,

Julian

Yessir!

Julian is correct, of course, the rivet heads need to be soldered and it's a lot easier if they are loose-fitted. I will dish the heads with the dremel, flux up and solder before going to the next operation.

Meanwhile, I have made the girder stays as per drawing. First, I bent up a couple of lengths of 3/4" angle from the copper offcuts, shaped the ends and drilled the six half-inch clearance holes for the cross-stays, remembering they are left- and right-handed. Next they were clamped together, three 3/32" holes drilled and then riveted with copper rivets. These are entirely within the water space and need no special attention.

I then stood the assembly in the upright "T" position, laid a length of high temperature silver solder in the gulley and did a cook-up. They don't really need soldering together, I just fancied using some gas, but it did have the added advantage of annealing the copper again.



The assembly was then placed on top of the firebox, clamped at the front and a pair of 3/32" rivet holes drilled right through, one front and one back, to keep the girder in position during soldering. Rivets were loosely laid in the holes with a tiny ring of solder underneath and the girder melded to the top of the firebox. It was then set up in the hearth at about thirty degrees with a couple of lengths of solder up the gully for the lower leg and one on the top edge for the upper leg.



Heating was done from inside the firebox and below the girder until we had a full melt. After the box had cooled for five minutes, the cinder blocks were cleared away to speed up cooling.



As can be seen, the rivets are standing proud of the girder where the solder melted away, and these can be dressed back. Full penetration has occured with solder visible inside the firebox. (Hope you're watching, Julian.)



The outer girders were marked out on the plate...



... then cut to shape with a hacksaw. These will not be machined, plus or minus an eighth of an inch is fine for this.



A couple of sessions of annealing and bending got to here...



...continuing until they matched the end view on the drawing. Then they were set up on the mill and the half-inch holes drilled as before. When fixed to the top of the firebox, these holes need to be aligned to allow the cross-stays through.



Three rivet holes were drilled in each girder, then these were clamped (with difficulty) to the top of the box and spotted through. 8BA nuts and bolts were used temporarily to hold them in place while the bottom lips were teased to the shape of the firebox.



These will be removed and loose rivets set in prior to soldering.



If I were to do this again, I would get these girders affixed before putting the firebox backplate in, this would make it much easier to position and clamp the girders to the top of the box. As it was, I was faffing around a good while before I was happy with the job.

The two girders are slightly different sizes and some steel plates and G clamps have been employed to help straighten things up. And I couldn't resist resting the tube assembly in position for a final photo.



Getting there, slowly.

Steve

[delaplume]

Hi Steve

From the Latin we have}----- "ut re vera est, apes genua erigite" !!!!!

Well done so far...

[jon38r80]

What have monkeys in Genoa got to do with it? Sorry, didnt have an education in classics but I know it basically means 'the bee's knees'. Agree wholeheatedly. I wish my sheet metalwork and silver soldering were that neat. looking forward to you getting its "skin" on. I really enjoy the level of detail in your posts.