Welcome to
Steve's Britannia
1.1/2" scale Allchin Traction Engine
Boiler and Fittings
  1. Boiler - first checks  
I've made a start on assembling the boiler and a few measurements show that there is still quite a bit to do. The silver-soldering is a bit scruffy and I have no idea whether or not it is sound. Also, this was soldered together in the 1990's so there is a fair chance that the solder used is cadmium-based. Hopefully, the thing won't fall to pieces when I continue with the modern, higher temperature cadmium-free solder. The first thing that needed attention was the firebox outer wrapper.
There is a dimension from the top of the boiler to the base of the firebox but the outer wrapper has to sit 3/8" above this and I think Jack misread this dimension. I marked it out on the surface table then removed the surplus with a hacksaw. When it comes to joining the two parts of the boiler together, Hughes suggests that the throat-plate segment of the foundation ring is fitted first using a couple of rivets. Drawing on my experience with the Britannia boiler, I chose to fix it with a couple of 6BA countersunk brass screws instead. I won't fix anything with rivets after the hassle we had earlier, and brass is fine here as they are not in a water space.
Then it was on to the firebox and this needed to be reduced in height also. To make matters more complicated, the shape of the box was trapezoidal rather than rectangular so it needed to be thumped about a bit to get it looking right. Then I loaded it into the milling vice and checked for uprightness and the height from crown to base measured. This next picture shows how I held it, clamped onto the girder stays.
The method of workholding is a little risky, to say the least, so an additional safety clamp was added in the form of a solid bar passed through the firehole and resting on vee-blocks both in and out and an overhead clamp keeping it all firmly in the vice. Now I felt confident in milling all around the base to get the height correct. The 3/8" deep cutaway at the throatplate section of the box was also remachined. I won't use the term "front" because, to loco men the front is the smokebox end but to traction engine men it's the firehole.
The two parts were offered up together but the girder stays were too high and forcing the inner section downwards with respect to the outer wrapper. To get the two components to sit comfortably, the girder stays were adjusted by judicious use of a heavy hammer and round bar to sink the centre inwards somewhat. The next job I tackled was getting the firebox square at the base. I used the wrong term before, I meant rhomboidal (if that's a word) rather than trapezoidal and this was achieved suprisingly easy with a large "G" cramp. The copper is much more maleable than I would expected after thirty or so years.
Onto the backhead and this needed reducing in width. All the materials have been specified as 13 swg (3/32") so far but this, along with the frontplate, are made from 1/8" copper and look to be professionally made so were probably purchased from Reeves. This made it an easy task to mill an equal amount off each side without weakening the plate. Once milled, I scribed a centreline on the backplate and offered it up to the outer wrapper. The size was as expected, 3.11/16", and the centreline will be used to set the position of the firehole.
I'm going to hold the girder stays to the wrapper using four 4BA countersunk PB screws and I was able to tap the girder stays around a little bit until I was happy with the position of the firebox. Hole positions were then marked on the top of the boiler and the the parts disassembled. The four clearance holes were drilled first, then the boiler reassembled and the holes spotted though, drilled and tapped 4BA. Even I remember that, occasionally, machine tools are not the ideal tool of choice. With some temporary steel bolts holding the girders in place and clamps holding the bottom together, it was time to get the backhead into place. But first, the firehole ring had to be adjusted because it was too high. It should be level with the back of the outer wrapper. The screws held the assembly firm enough that I could use a drift to ease the firebox wall inwards until the firehole ring was level.
The backhead was offered up so that I could scribe through the firehole, a job that really calls for small hands. It's a bit tight in there. Then I stitch-drilled a load of 3mm holes around the perimeter.
The waste was cut out with an Abrafile and the hole dressed to size, starting with a rough file and finishing with sanding drums in the dremel. More work was needed on the frontplate including holes for the decorative rivets around the firehole, three holes for some blind bushes to carry the firehole door and it's catch, ten holes for the stays and cutting the bottom off to length. Apart from the two on the centreline, the firehole rivets were drilled by eye as I could find no dimensions given anywhere.
The water gauge bush had already been made but I needed to make the three blind bushes and these were made from 5/16" diameter Colphos. It's much nicer to machine than phosphor-bronze and is perfectly OK for this job. The O/D was turned first, then a 1/4" x 40 button die run down and finally parted of with a 1/16" shoulder. Screwed back into a tapped bush, the 7BA thread was drilled and tapped, stopping the drill at 1/4" deep. The frontplate was fitted to the firehole ring and clamped with a pair of penny washers and an M8 nut and bolt. The vee-block clamp is a convenient way of getting over the firehole rim and ensures that the frontplate stays put while I drill and tap five 4BA holes in the sides and top of the wrapper and frontplate. These will be countersunk screws made from bronze as they are in the water space.
  2. Boiler - starting to solder  
Everything was placed in the pickle, including the copper rivets, and then rinsed off. Correction fluid was painted around the firehole area to stop all the silver solder running away when heated. Flux was painted into the rivet holes, the three blind bush holes and onto the bushes and rivets before assembly. The rivets were snipped to length and gently peened into the countersinks, hopefully leaving adequate room for solder penetration. Solder was stategically-placed inside the ring and the frontplate set up in a hearth. The plate is raised on blocks so that I can apply bottom heat and the whole thing is enclosed to retain whatever heat I can. A final helping of flux was applied generously around the area and the torch fired up.

After an hour or so in the pickle, this is the result. The correction fluid has done it's job and contained the solder and, apart from one rivet adjacent to the water gauge bush hole, everything has soldered well. I shall remove the dodgy rivet, clean the hole and start with a fresh one rather than try and resolder this one. The bush will be done at the same time.

With the front plate drilled it was time to drill the rest of the stay holes in the shell and firebox. The throatplate holes were marked out with a vernier caliper and then centre-popped, no real accuracy here as they are hidden behind a dummy thoatplate. I silver-soldered a 1/8" drill into a length of mild steel to give me an extended drill.

The inner and outer were then reassembled, along with the frontplate, screwed and clamped into position, adjustment being made to get the firebox central within the wrapper. The front and rear stay holes were drilled first, loading temporary steel rivets into the holes as the job progressed. Once these were in place, the assembly was offered up to the hornplates and the side stays spotted through with a hand drill. The pump feed bush and blowdown bush were also marked out. Then all the holes were opened up on the mill. Due to years of handling, the tubes were all out of position and a couple out of shape as well. I used the drill jig that father had made, opening the holes up an extra 1/64", and worked this down to nearly the bottom of the tube nest. Then the tubeplate was offered up and the tubes teased into position. In the picture, I have the tubeplate upside-down.
The tubes were quite a tight fit and needed to be eased somewhat to aid assembly. First, the tubeplate holes were cleaned up with a sanding drum in the dremel, then the drill jig was brought up near the top for support and the tubes given a clean-up with emery cloth. After assembling everything together, it became obvious that the smokebox tubeplate was going to give trouble because of it's poor fit and because the barrel is slightly tapered (narrower) at the front. It's impossible to fit the tubeplate from the firebox end so I'm going to solder the plate in first and load the firebox and tube assembly later. In the meantime, I've also decided to fix the longitudinal stays to the frontplate now, rather than try and locate them later.
Before joining the two sections of the boiler, there are a few more parts that need fitting first. The pump inlet and blowdown cock bushes were fitted next and I also found a small hole between the barrel and the wrapper that needed filling. A tiny wedge of copper was banged into here and all three things done at the same heating. I've buried as much of the boiler as possible to help keep the heat in. Some people think that's a waste of time but I find I get up to temperature much more quickly and, therefore, don't exhaust the flux. I usually leave the workpiece covered for a few minutes rather than risk rapid cooling. This is after fifteen minutes and it's just about cool enough to pick up with bare hands.
  3. Manifold Pad  
I made the mounting pad for the steam manifold from an old, scrap gunmetal casting. This pad is 7/8" square and needs to sit on top of the outer wrapper. After milling all round to get it square, I needed to dish the underside to match the 3.750" diameter of the barrel. The billet was mounted at one end of the vice and a packing piece (a Hoffman roller) at the other end. Using a boring bar in my boring head and adjusted to the absolute maximum is just a little shy of the required diameter but it will have to do. Four cuts of ten thou on the "X" axis just using the quill completed the operation.
Then the pad was set on parallels, clamped tight and the parallels removed. The four holes for the mounting studs were drilled, followed by a 5/32" hole in the middle and a 1/4" wide slot to clear my frontplate clamping screw. The holes were tapped freehand 8BA: the drawing says 7BA but I think that's a touch too big. To protect the tapped holes, I have screwed 8BA bolts in and put a spot of correction fluid on the underside to stop any solder filling them. Flux has been painted over the rest of the area and on the top of the outer wrapper.
The pad was held in place with a sacrificial spring clip, a horseshoe of solder placed around he outside and more flux added. I set it at an angle so that I could apply heat from inside the wrapper but still have gravity working in my favour and see what's going on. The manifold mounting pad was not as successful as I'd hoped. There was a hollow at the back of the pad and when I put the airline to the steam hole water bubbled out from underneath where the arrow points. A clamp was fitted to the front of the pad, the work re-fluxed and another piece of solder set in place. The second attempt was satisfactory and the steam hole can now be drilled.
  4. Manifold  
The manifold had been mostly machined but it's base had been left at casting size and overlapped the pad. Holding on the edges, I first machined a pair of flats on the sides of the outlet pipe. The fitting was then upended in the vice and set on a pair of 1/16" thick packers at the end of the vice. The packers were removed, the work centre found and the edges milled all round to leave a 7/8" square. The four mounting holes were drilled 8BA clear at the corners and I also formed a recess for an "O" ring. The "O" ring is not featured on the drawing and a gasket would have been used originally. I have used a 9mm diameter by 2mm section ring and made the reccess 1.7mm deep. If it turns out that it doesn't seal well enough, a little more can be skimmed off the base. This is the manifold ready to be screwed into place.
  5. Tubeplate  
The smokebox tubeplate was soldered into place next using 40% silver solder and, although it has sealed all round, it has not formed as nice a fillet as I would like. This was followed by joining the two sections together, manipulating the tubes through the holes with a pencil and screwing the crown stays and front foundation ring section into place for accurate spacing. In the next picture, I have placed solder rings around the tube end and you can see where a bit more solder is needed on the perimeter. The correction fluid is to prevent solder flooding away to the top of the boiler. The tube at the top right is just flush with the tubeplate and will probably cause the solder to flow down the inside of the tube so an extension piece was made from more copper tube, the inner section being the next size down. It was cut off about 1/2" long overall and cleaned up really well before placing in the short tube.
Learning from our experience with the Britannia boiler, I set everything up as shown in the next picture. The small butane kit clamped in the workmate supplied continuous heating into the firebox and ensured the tubes got nice and hot. The biggest problem we found before was that the tubeplate got hot and the solder puddled all over it but the tubes didn't get as hot and the solder didn't take very well. The next picture was taken a few minutes after removing the heat and it looks very encouraging. After five minutes cooling, I removed the surrounding insulation and left it until I could hold it in bare hands, then placed it into the pickle for an hour or so before giving it a really good rinse.
  6. Boiler Stays  
I decided to fix the throatplate stays first and these were made using 1/8" diameter copper rivets. They were loaded from inside the firebox and solder rings placed on each in the waterspace before the rivet was pushed through to the outer skin and a second ring placed on the outside. Flux was painted onto the rivets both in the firebox and in the waterspace, then the rivets pushed fully home. A dimple was crimped into each to keep them in place when upended. With the assembly resting on the firehole, the rings were pushed down to the surface and loads more flux applied. The it was carried through to the hearth and surrounded with thermal blocks. Heat was applied inside the firebox until the lower rings flashed, then the upper rings followed shortly due to conducted heat.
After an hour in the pickle this is the result. Solder has migrated through to the inside of the firebox and formed a perfect joint around each of the stays. And on the outside, the solder has left a nice fillet around each of the stems. I can see that solder has flowed through to the waterspace but the camera is unable to capture the detail. This method appears to give good results every time and, hopefully, the rest of the soldering will go as well as this.
  7. Crown Stays and Frontplate  
Soldering up the girder stays was next and, as with the Britannia, were a pain in the rear, needing three visits before I was happy. The advantage of using bronze screws to hold them in place means you can test the screws afterwards. If any unscrew then there is not enough solder and another heat-up is required. Then I hit a problem, one of my own making. All that fiddling with the girders had distorted the wrapper by a small amount and needed to be teased back to the shape of the frontplate. However, I had already soldered in the longitudinal stays and this made the job many times longer because I had to keep loading the stays through the smokebox tubeplate, which was a fiddle. I used this method for locating them, bits of plastic tube of varying length fitted over the ends.
This method works for the Allchin boiler because there are threaded stay bushes at the tubeplate so the holes are a lot bigger. This made it fairly easy to assemble but didn't help much with easing the wrapper as the frontplate had to be removed completely each time to tap the copper from the inside. However, I managed to get a decent fit in the end and set up for soldering. To help keep the solder in place, I filed a chamfer around the inside perimeter of the wrapper to create a tiny gulley, and the same again around the firehole. Setup was as previous so I took no photos of that but this is the outcome. I'm particularly pleased with this effort. The five fixing screws have passed the test and there is a nice fillet all round the perimeter and around the firehole, all in a single session. One new lesson in the art of boilermaking has been learnt, though. Don't solder things together until they are needed. Soldering the long stays to the frontplate before doing the crown stays was a mistake as I would have been able to reshape the wrapper much more easily if those stays weren't there. Just before joining the frontplate to the wrapper would have been the right time.
  8. Side Stays  
The stays to the front plate have now been soldered, duplicating the work done on the throatplate. As before, solder has migrated through the holes to form fillets either side. Attention then turned to the side stays. These are bronze screws with a 1/4" x 40tpi thread on them, thirty two in total. They are threaded through both the inner and outer skins and are designed to be nutted on the inside and soldered with comsol. However, if silver solder is used the nuts can be omitted. Hughes recommends making a special tap for this job and one was duly made using 1/4" dia silver steel, turned to 7/32" dia at the front for 7/16" and threaded with a button die. On the mill, a collet block was used to index round and cut the flutes.
The turned section is to enable the tap to be perfectly aligned with the inner hole before cutting the outer hole. The cutter was then moved up and over to further relieve the flutes but the photo of this is too blurred to use. After hardening, then tempering to light straw, this is the finished article. The cutting lead was freehand-ground after the picure was taken. My tap was a little undersize so, after each hole was tapped, a manufacturers tap was run through for sizing and the screws set into position. This ensures that the relative positions of the inner and outer skins stays exactly in place. A couple of the bronze screws that Jack made can be seen resting on the foundation ring.
However, after assembling the whole lot together, I felt that it was not possible to use my previous method for soldering the stays. The waterspace is too narrow and too far down to control solder rings on the lowest row each side. I decided to turn the heads to 1/4" diameter and put a small screwdriver slot in the ends for assembly purposes. With the foundation ring uppermost, two solder rings can be placed on each stay and, hopefully, will flow inwards to seal. I will find out if it works tomorrow! Meanwhile, I have cut off the stays on the frontplate and dressed them with the dremel to look like rivets. They don't need to be too precise, they are practically out of sight under the footplate.
I was going to try and do both sides at once but, in the end, I chickened out and did the job in two halves so that, once again, I had gravity in my favour. All the screws were set in place and the boiler laid over to about twenty degrees from the horizontal. Then solder rings were placed on the uppermost side of each one and well-fluxed. After cooking, it was pickle, rinse and repeat for the other side. It appears to have been successful but I won't be sure until I can pressure-test the boiler. This side is a little neater than the other side which has a couple of solder puddles. None of this is seen as the firebox sits between the horn plates.
  9. Foundation Ring  
Then it was on to making the rest of the foundation ring pieces, starting with the back and then the two sides. These are made from 1/4" square copper bar. A pair of packing pieces were for each side and fixed with screws through to the foundation ring, doing two jobs at once. Two further pieces were made which get fixed adjacent to the frontplate. After a really good clean-up, the foundation ring pieces were assembled into place and the boiler set up on the hearth with plenty of surrounding material to keep the heat in. Some tiny wedges were made from beaten copper wire to plug the small holes at each corner and hammered into place. I ran out of time today but, although the soldering seemed to go well, one of the wedges must have popped out because there is a hole at one of the corners. Tomorrow, I shall make a closer inspection and do whatever repairs are needed..
  10. Finishing Touches  
After a really good soak in the pickle to get right into any tiny crevices, I had another go at the foundation ring and, this time, all seems to be well. Then it was the turn of the longitudinal stays on the smokebox tubeplate along with more solder to the one tube that leaked from the first session. As before, I set the boiler up with the butane torch providing secondary heat to the inside of the firebox. This also helps to protect the tube joints from cracking due to differential expansion. After cooling and pickling, it looks like I've had a good melt.
This was the first time I've been able to perform any sort of test on the shell and a couple of things immediately came to light. First problem was this joint between the boiler shell and the outer wrapper. There is a collar underneath here but it leaked profusely so some copper wire was beaten flat, almost to foil, and set in the three visible sections. However, the other side was fine. The other place that leaked was the around doubling plate used under the cylinder. This doesn't need to be tight because, obviously, the hole get drilled through and provides steam to the engine. Sticking my thumb over it was enough to find the previous problem but not much good for the long term. So, for now, I have made a cover plate and gasket that is held in place with a large jubilee clip. The gasket didn't seal but a couple of "O" rings did the trick, instead.
I also discovered that one of my side stays had a pinhole leak so the area was cleaned up and repaired also. After that, I was able to lightly pressurise the boiler with the airline and a potentially fatal problem reared it's head. There were a few bubbles coming out of the joints between the firebox inner wrapper and the two end plates. it's not much but it could be a killer. I will discuss this with the boiler inspector and see what he suggests. This is one of the disadvantages of working with something that was soldered up about thirty years ago. There was no way to test these joints beforehand, nor is there any record of what solder and flux was used. Probably cadmium-bearing, which I don't have a problem with, but it probably also had a lower melting temperature that what we use today. So it could have been poor joints to start with or I may have disturbed the joints with my subsequent soldering operations. It may also be that a flood of comsol on the crown will allow the boiler to be used but I don't know.
  11. Side Stays modified  
I've chased down a few more weeps and am now ready to present the boiler to the inspector for it's shell test. There are a couple of places where water escapes but these will seal on their own, or with the help of a little ground white pepper. The test kit also needs a little TLC as it leaks back past both the lock-off valve and the pump. The next stage of the job was milling the heads of the stays and the packing to get a snug fit between the hornplates. The boiler was set up on packing to get it as even as possible, then the first side was skimmed down using a home-made flycutter. I took about thirty thou off this side. A single clamp in the firebox was enough to hold it in place.
The boiler was flipped over and the other side milled to bring the width to 3.812". Then it was offered up to the hornplates and this was a very time-consuming job. Hughes designed this boiler to have hollow side stays so that a rivet could pass right through and fix the boiler without disturbing the integrity of the shell. Therefore, positioning was all-important to ensure that the boiler went back to exactly the same place as it was when the side stays were spotted through. A flat piece of MDF was laid on the mill table and the 3/32" dia holes drilled through freehand, dropping a steel rivet into each hole as they were done to control any movement. Drilling the other side meant resting on the rivet heads but this presented no problems.
I was able to get some 3/32" copper rivets that were 1" long and, rather than rivet the hornplates to the shell, I have chosen to thread the ends 7BA and put nuts on the inside. This allows for future disassembly. A split brass collar was made to hold the rivets for threading in the lathe. As each rivet was converted, the short steel rivets were withdrawn and the hole redrilled with a pistol drill. Getting a hand into the depths of the firebox to fit the nut was a bit tight and the rows nearest the crown were done first. With all the rivets in place, this is the current state of play. The ends need trimming to length but there are a few more holes to drill before disassembly.
  12. Firehole Door  
The firehole door needed to be made and there were many small parts make. None of the parts were particularly difficult to make but the most fiddly parts were the door latch and keep. The hinge, hinge pin and brackets were quite straightforward. Assembly was a little tricky and needed to be done in the correct sequence. Importantly, one of the rivets on the hinge also held the baffle plate and had to be one of the last to fit. The baffle plate had to be dressed to fit the firehole after assembly. It needs to sit 1/32" clear all round to allow secondary air to enter the firebox through the centre hole in the outer door.
  13. Ashpan and Grate  
The ashpan and grate also needed completing and the Allchin boasts a dropping grate for easy disposal of the fire. The first thing I needed to do was make a pair of pins to support the fire bars. 1/8" diameter mild steel was cut to length and a No.1 centre drill used to make an internal cone at each end. I originally tried using stainless steel tube but it proved to be too soft.
This allows for a punch to spread the ends and hold the assembly together and decent countersinks were made in the outer firebars to form a seating area. The firebars were assembled on temporary pins with the spacers in place and with the brackets connecting them to the ashpan lower door. The countersunk pins were pushed through, diplacing the temporary ones, and the ends bell-mouthed using a couple of lathe centres and a big hammer. The lower door was then bolted to ashpan and the whole unit became self-contained. to the left can be seen the front damper that allows extra air into the firebox.
When the catch is released, the rear of the door drops down to deposit the fire on the ground. Also seen in this picture are two of the four mounting holes. Hughes suggests drilling and tapping half-a-dozen holes into the foundation ring to hold the ashpan in place and three of these holes can just be seen in the flange. I think this is an unneccesary risk and decided to drill a pair of sideways fixing holes and screw the ashpan to the extended sides of the firebox instead. With these items completed, I can now assemble the boiler into the hornplates for the final time and get on with the boiler cleading.
  14. Next Item...