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Steve's Britannia
5" gauge Adams O2 - Calbourne
Drawing E1(a). Drawing E1(b). Drawing E2(a). Drawing E2(b).
Drawing E3. Drawing E4. Drawing B1. Drawing B2.
Drawings S1 and S2 Boiler Assembly Assembly and Alignment Errors and Ommissions
Assembling the Boiler
It's a lot easier to have someone helping when silver-soldering large lumps together and my friend Wilf joined me for our first session of soldering to start bringing the boiler together. The first job was to join the firetubes and superheater tubes to the firebox frontplate and to fix the firebox outer wrapper, all in a single heat-up. All the parts were pickled for a couple of hours beforehand and then we fluxed up all the parts and assembled them together. Solder rings were made for the tubes and placed on the outside of the frontplate. Solder was also placed in the join around the perimeter of the firebox. After the tubes were in place, the tube support was clamped to the frontplate and the assembly carried through to where we'd built our hearth. I meant to take a picture of the preparations but got carried away and forgot all about it.This first picture was taken a few minutes after we removed the heat completely.In that picture, a white area is visible below the tubes.This is where I painted correction fluid on the frontplate to stop the flux and solder running away. If the flux dribbles away, the solder always seems to follow it.
Moving on, Wilf used the cyclone burner to heat the inside of the firebox and I used a normal burner to heat the sides and top of the wrapper, starting gently. As the colours started to change we increased our flame sizes and watched to see the solder just start to glisten. At this point, I backed away a little and let Wilf use his heat to draw the solder down. The next picture is from the back of the setup and shows the tube support plate. I'd forgotten to spigot the two 22mm tubes so a pair of small clamps stopped them falling intp the firebox. The block on top of the tubes was to help keep the heat in, otherwise all Wilf's efforts would be going straight up the chimney, as it were. Once that had cooled sufficiently to be held in bare hands, it was placed in the pickle and left for an hour or so.
Meanwhile, we fitted the two clack bushes to the sides of the barrel with 40% solder. This time, the solder ring was placed on the spigot of the bush and the bush rested in the hole. As usual, correction fluid was painted onto the face of the bush and also the thread. A nudge with a prodder as the solder melted ensured a good seat. Back to the firebox and a good, all-round inspection. We couldn't see any daylight through any of the seams and we appear to have good penetration through all the joints. I will now get the boiler inspector to check over all the soldering to date and, if approved, we will get the throatplate and outer wrapper fitted to the barrel next week, along with the dome bush.
The first job of the day was to solder the dome bush into the barrel with 40% silver solder so Wilf prepared the parts with correction fluid in the threads and around the barrel opening whilst I made some more 6BA countersunk copper screws ready for the next job. This was set up in the hearth with the dome bush resting on a packer and with the solder laid around the bush on the inside of the barrel. Heat was applied from the outside only. While this cooled, we then prepared to close the firebox by soldering the backplate into position.
This was set up on the hearth so that the tubes hung over the edge of the blocks with a weight keeping the assembly balanced. 55% solder was placed around the perimeter and heat applied mainly inside the box by Wilf with the cyclone burner and me adding extra heat to the outsides of the firebox. As the solder melted, I moved away and left it to Wilf to draw the solder down. The block in the opening is to protect the tubes from unneccessary heating.
With the barrel cooled and pickled, we then set about assemling the throatplate and the outer wrapper to the barrel. Preparation for this took quite a while as, once lightly screwed together, I had to do a bit of light tapping to gently ease the edges of the wrapper and throatplate together. It's easier to do this with the flux already between the joints and then add more afterwards. A pair of small clamps were added to the bottom corners to stop these edges springing apart. Same procedure as before and this is after the melt has occurred.
This one I'm particularly pleased with. The wrapper and throatplate to barrel joints are nigh-on perfect with full penetration but no wasted solder. Most of the credit for these goes to Wilf because he did the majority of the preparation while I was fiddling with screws and other odd jobs and, without good preparation, we would not have this level of success. One other point on preparation for others who may be encouraged to have a go. Regardless of how clean they look,I always pickle the copper parts for about half-an-hour, followed by a rinse in clean water, just before fluxing up. I know the job of the flux is to clean the work but I think the extra effort is worth the time spent. In the words of Mr Tesco, "Every little helps".
The boiler inspector was happy with all the soldering so it was now time to start bringing the two sub-assemblies together. One of the first jobs was to machine the firehole into the backhead because that helps to position the firebox correctly. Luckily, it's a circular firehole rather than an oval one which requires a lot more work to get a snug fit. This is 1.1/2" diameter. The tube support was modified so that it fitted the barrel correctly and the tubes, which had become squashed together, were reworked to their correct positions. The firebox assembly was loaded to the barrel and the backhead placed into position.
The firebox was clamped to the throatplate and the backhead with packing pieces and adjusted until square. After the next picture was taken, a small clamp was used through the firehole to keep the backhead tight to the firehole ring. The rule under the dome ring ensures the barrel is parallel to the table. Then the backhead fixing points were drilled and tapped 6BA, all done freehand with a pistol drill or hand-drill. With this complete, the firebox assembly was removed, the backhead put back in place and the positions of the stay holes marked out. All the stays are on a 9/16" grid and will be made using 1/8" copper rivets except for four extra ones which I've added to the backhead and the ones that will replace the girder stays on the crown. These will be 3/16" diameter. While I had it disassembled, I also dressed the inside end of the barrel back to the throatplate.
The first holes I drilled were the front throatplate and I was able to use a homemade drill that I cobbled together when doing the Allchin boiler. However, because of distance and clearance issues, I had to remove the backhead to get it to work. It's a 1/8" diameter drill silver-soldered into a length of 1/4" diameter mild steel rod. Because the backhead was out, I drilled that freehand on the drill, using the MDF former as support while centre-popping and drilling. Then it was bolted back into the outer wrapper to provide support while doing the side holes. Three rows of holes are within the curve of the wrapper but I want them square in the firebox so I did these on the mill with a slot drill instead. Although the grid was there to guide me, I actually used the DRO to position them.
The boiler was reassembled, still using the tube support at the front, and the base of the firebox centralized in the wrapper. I made a couple of screws to fit the blowdown bushes and used these to keep things in place. Then I started the laborious process of drilling all the stay holes in the firebox. They were all done with a pistol drill and a rivet dropped in to test the hole as I completed each one. This is not how they will be soldered; the heads will be on the inside and the outer tails dressed back to clear the frames. The four holes that are unfilled in the backhead will have 3/16" rivets instead and I will drill and tap these 8BA, keeping the holes blind. They will be used to fix the plate for the firehole door and rails.
That just left the crown stay holes to be drilled and these needed to be inclined so that they spread the spacing correctly on the top of the firebox but not interfere with the bushes. A large vee-block was set up on the mill and the assembly clamped to it at an angle of 12 degrees. The holes in the wrapper were made using a 3/16" slot drill but the holes in the firebox crown were very carefully spotted with a 3/16" drill because of deflection. They were then drilled through with a 4.4mm drill followed by a 3/16" reamer. Because the stays are from 3/16" dia copper rod, the spacing can be increased to 11/16" but I chose to use a spacing of 5/8" for extra support. This next picture shows how the crown stays are spaced in the firebox. All that remained was to dismantle everything and deburr all the holes. There are still a couple of holes to sort out in the backhead for the water gauge but this can be done later.
The two halves of the boiler were pickled for an hour, as well as sixteen copper rivets, and Wilf made forty or so silver steel rings on the lathe using 1mm rod and a 3mm former to wind them on. While he made those, I assembled the two halves using the backhead to get the firebox in the correct position and pushing a couple of rivets through some of the side holes for additional alignment. Starting with the lowest row, a 1/8" drill was passed through the first pair of holes to check clearance, then flux was painted in with a tiny brush. Wilf held a solder ring in the water space in line with the hole using a special pair of pliers that we had made for the job. I fluxed up a rivet, pushed it through from inside the firebox and gently tapped it fully home. On the outside, a pair of flat-faced cutters were used to indent the rivet and keep it in place, then a second ring was placed on the outside of the rivet and more flux added. This was repeated until the first row was complete, even more flux added, and the procedure repeated until all the rivets were in. This is part-way through the second row.
With all fifteen rivets in place, we fluxed up all the nearest seams that had previously been soldered and checked that all the solder rings were sitting down flat. The packing piece in the next picture is to make sure the gap doesn't close during soldering - there's not much chance of recovering from it if the inner moves relative to the outer. Then it was set up in the hearth. Blocks were place all round and another one on top to cut down heat-loss although the dome bush was left clear to allow burnt gases to escape. The gaps to the sides are there for one of the burners to heat the outer wrapper while the other one applies heat to the inside of the firebox. The whole thing is built up on a workmate so that we have a comfortable working height.
The heat-up took about ten minutes and we kept applying heat until the last solder ring flashed, the outside ones furthest from the foundation ring taking the longest because it was difficult to get the heat down the water-space. I was using a fairly slim nozzle on my burner to produce a narrow flame while Wilf was using a cyclone burner to apply the heat inside the firebox. The biggest problem we found in the past was starving the burner of air when working into an enclosed space and a cyclone nozzle overcomes that. After cooling and pickling in citric acid, this shows how the solder has pulled through to the inside. All fifteen rivet heads have a nice fillet around them. It's not so easy to see the down into the water space but the solder has gone from the outside without forming puddles around any rivet tails so I'm happy that we have good penetration. However, the rivet at top right in the next picture doesn't appear to have a perfect seal so I will put another solder ring on there and give it another heat-up.
Wilf came over on Friday and we were able to get the next lot of stays soldererd into place. Preparation for this took the best part of two hours because of the difficulty getting solder rings on the deepest stays. I haven't bothered to write this up fully because it's just a repeat of the previous but the next three pictures show our progress. The first one shows a view into the waterspace where it can be seen that solder has flowed through the joints. The next one is a view of the outside. DY shows the expansion support bracket screwed to the side but I've chosen to solder it with the stays coming through. I suspect his idea was an afterthought.
The last one shows a view inside the firebox with all the rivet heads neatly soldered. It was easier to get the heat in this time because we didn't need to use the backhead as a support, the box already being held firmly by the throatplate stays. Last week we soldered all the stays on the other side of the firebox but it was just a repeat of the previous weeks work. The one photo that might be of interest is the boiler in the hearth just before lighting the torches. The cyclone burner was used to heat the inside of the firebox and the normal burner fed heat into the water space from the back.
I had also previously made a steel plate to cover the tube ends and give them a bit of protection from the fierce heat. The thin wall of these makes them more vunerable to overheating, leading to a damaged joint. A length of M6 stainless steel studding passes through one of the flues to keep it in place and the rod can be drawn out through the firehole if the nut gets jammed at the firebox end.Then we fitted all the crown stays, which replace the girder stays that DY had specified. I made these from 3/16" diameter copper rod because rivets of the required length were not available. After parting off, one end of each was gently hammered over to form a mushroom head. A close-fitting washer protects the collet and limits the spread of the copper.
The stay spacing is greater than on the sides because the larger stay sizes allow for a larger grid pattern but the dimensions used reflect those in the Australian boiler code for these sizes of material and operating pressure. They are also superior to the girder stays because of the stronger through-joint compared to the butt-joint of a girder stay. One unusual thing were the four additional stays that I've added around the firehole. I wasn't happy with what was shown on the drawing and these additional stays perform a dual function. These are 3/16" diameter copper rivets that have had the heads thinned down, then cut to length and the core drilled and tapped 8BA and will be used to fix the firehole door panel to. The unusual bit is that I've opted to solder them to the firebox now, rather than when the backhead goes on because they would have been extremely difficult to get to later on. This next photo shows them in place.
With it all cleaned up, here is a view through the crown before the backhead goes on. The angled stays are to allow enough room for the regulator tube to pass freely through, with the blower and air-brake stays passing by on the outward sides. Also, the firehole door fixing points can be more clearly seen. And this final picture shows the backhead temporarily in place. The four backhead rivets are nice and soft so easy to align. Once the backhead is soldered up, they will be trimmed back to flush and the thread re-tapped. By doing it this way, I don't have the risk of trying to drill a blind hole in the rivet and/or breaking a tap in there at the last moment.
At the next session we able to get the front tubeplate soldered into position. It took a little while to align the tubes because I missed a trick when I bored the barrel. I should have relieved the front section by an extra five thou and this would have allowed the tubeplate to wobble about a bit easier. Lesson learned for next time. Happily, we've had a good melt. Then we went on to fit the backhead. Bushes, firehole and most of the stays went without a hitch but there was a small area at the top of the wrapper that needed resoldering which didn't come to light until the boiler had been thorougly cleaned. During the heat-up, the solder resting on the lip fell off and I had to resort to the dab-it-in method but this is generally not very successful for amateurs like me and Wilf..
The next job was the foundation ring. I had made all the parts earlier in the week so it was just a case of fluxing up, setting them in place and teasing the wrapper for a nice fit. I have some flat silver solder that had been given to me and was told it was Easyflo, so pretty similar to our usual stuff. Here is the set-up in the hearth. The foundation ring pieces are set just below the level of the outer wrapper so it's like a shallow moat all the way round. There's actually quite a lot of solder there because the stuff is 5mm wide x 1mm thick. I had filed a chamfer on the outer edges of the four pieces to encourage the solder to flow down the gaps. Here's another view from further back showing how much effort we go to setting things up. This is all to conserve heat but also keep it mostly where it's needed.
We started with two normal burners but kept blowing each other's torch out so Wilf went back to the cyclone burner and worked inside the box while I heated the outside. Once we were nearly up to temperature, we concentrated our efforts at a single point on one of the sides, then slowly worked our way round chasing the melting solder until we were back at the start. That was it, finished. It looked like a pretty good melt but it's always hard to tell until the thing has cooled and been cleared up. Immediately after that last picture was taken, a further block was placed on top to slow down any localised cooling. Wilf left soon after this and I allowed it to cool for about 45 minutes before washing and pickling. This is the result and it can be seen that it's gone well. All the solder has vanished instead of puddling on top and all the gaps are a lovely, shiny silver.
It looked like there was a tiny gap at the back of the foundation ring so we re-soldered that just to be sure of a seal. After cooling and pickling, we bunged up all the bushes and started to pump. We had all the usual weeps from the blanking plugs but once we had got that settled down, we wiped everything dry and took in stages up to 160 psi. After twenty minutes pressure was still just over 150psi but everything was bone dry so it was probably back leaking past the pump. After that, I dressed back the crown stays and the extra firehole stays to make it look pretty in preparation for it's official shell test up at our club. This is the completed boiler.

The boiler passed it's shell test (2x hydraulic) on 23rd November 2022 and the loco will, hopefully, be completed during 2023.