Welcome to
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
Drawing B2- Smokebox, Ashpan, Firehole, Fittings etc.
  1. Smokebox  
The smokebox on Calbourne doesn't use a piece of pipe or tube as the mainstay and is a fully-fabricated affair with an outer wrapper formed around two end plates. The wrapper is formed in similar fashion to a firebox outer wrapper and does throw up some interesting challenges, not least the making of a reasonably airtight seal around the cylinders. Apart from a few basic dimensions such as diameters, the majority is "fit to place", Don Young's way of saying he didn't really know what size it should be. The drawing shows to make the rear plate out of copper sheet and flange it like a backhead but Calbourne has a crisp, square edge at the rear perimeter of the smokebox so I silver-soldered a flange around the outside instead. The basic shape was marked out on the sheet and the hole for the boiler ring cut to size first. The ring gets soldered to the backplate later on.
A 3/8" wide strip of copper was cut from an offcut from the Britannia boiler, annealed and formed around a 4" diameter former, then the reverse bends eased in freehand. Once happy with with the shape, everything was pickled then silver-soldered together. Allowance was made for the thickness of the outer wrapper. After cleaning up, the outer edge was linished to the finished shape and the boiler ring fitted to check that nothing had distorted. The holes in the flange were already in the material and won't cause a problem.
The outer wrapper was made from 16swg mild steel and formed around a lathe chuck until I had a nice fit around the backplate. The tails are a good inch overlong at the moment as I don't yet know where the centreheight should be, and the I mustn't forget the incline of the cylinders. This is resting between the frames to check the width. I needed to make a ring to fix the frontplate to the wrapper but didn't have anything suitable in the workshop so a quick trip to the local garage and I came home with a pair of brake discs and a wheel hub. The hub was used to make the ring but, in hindsight, I should have chosen something a bit more machinable. First of all, I hacksawed off the front and that took the best part of an hour. The bearing ring is still sitting on the boss.
Over the next hour or so, metal was removed using small cuts, a medium speed and the auto-traverse. You can see how tough this stuff is by the colour of the swarf and I must have gone through half-a-dozen carbide tip edges to get this far. The interrupted cut didn't help much, either. All the facework was done with a boring bar but I've changed tools in the next picture, in preparation for facing the back to finished thickness. The back was faced down in ten-thou cuts to leave a 3/8" wide ring and cutting 1/8" past the finished-bore size. The racking handle on the lathe saddle is not very sensitive so a plunger clock was set up to keep track of cut size although I could just as easily have used the compound slide.
With all else to size, the ring was trepanned off and that was hairy! Very slow and very, very gentle but it came away clean. The cut line was bang in the middle of the holes so I didn't dare use any rake on the tool in case it got dragged in. From this point on, it was a long-winded process getting everything to fit together properly with a row of rivets around the smokebox perimeter into the ring, making the front plate, blind rivets because of their position etc, etc. This is the front plate which is screwed to the ring from the inside, along with the clearance gap in the ring for the steam chest. Getting things done in the right order was imperative.The items have also been phosphated. With these parts assembled, the fit to the frames was checked again and the profile filed until the smokebox sat upright and at the correct height. Calbourne has flat-faced rivets on the smokebox and the ones on the face are offset between the ones on the perimeter so it meant a lot of fiddling about to get them looking right.
Following on from this, I silver-soldered the boiler ring to the backplate. I've also fixed the wrapper to the backplate with eight 9BA screws (because they need using up) fitted from the inside to hold it all together. With the assembly sitting in the correct place, I spotted through the frame fixing holes, although I shall only use five of the seven holes because the front one is too close to the cylinder top and the back one is behind the wheel. I will be using M3 countersunk screws for this because the splashers sit tight to the frames.
I've also put the chimney hole in the top of the smokebox. An MDF former was bolted to a large faceplate and trued up on the mill. With it all safely clamped up tight, the hole was opened out using ever-larger slot drills and then finished off with the boring head. The chimney liner, made from an old piece of gas pipe, was used as a gauge.
  2. Chimney  
There is a casting available for this loco but I decided to make mine from various offcuts of brass and bronze. The first of these was the base section which came from a large bronze gear wheel. After facing off, the billet was bored through at 1.1/8" diameter and then opened out to 1.1/4" diameter by 3/4" deep to take the peticoat pipe. The first picture shows it resting on the soft jaws that I machined to hold the work for the second operation. The o/d was turned to the maximum size of the chimney saddle, then the 13/16" radius flare was formed using a technique from the very earliest days of turning. A round-nosed brazed carbide-tip turning tool was chosen and a 3/16" diameter hole drilled and reamed through the shank 13/16" from the tip. The toolpost was removed from the lathe and a worktable bolted to the compound slide in it's place, which had a 3/16" diameter silver-steel pivot-pin fitted at the top left corner. The turning tool was fitted onto the pin and a length of steel box-section slid over the back end of the tool. The picture isn't very good but shows most of the relevant detail.
This next picture shows the radius about half-formed and a better view of the tool with it's extension handle. There was no real measurements here, just easing the cut along or down twenty thou at a time and keeping pressure on the handle so that it didn't dig in to the work. Loads more cuts were made until I reached a point 1/16" thick at the base and 1.13/32" diameter at the chimney neck. Then a spigot was turned to locate the chimney onto. Bear in mind that this radius is only relevant to the widest part of the saddle and further work will be required once the underside of the saddle is machined to fit the smokebox.
Next, the chimney neck was made from a length of 1.1/2" diameter brass bar, drilling and boring through to finish at 1.1/8" diameter. A spigot to match the saddle was machined on the end and the outside cleaned up with emery cloth. The two parts were silver-soldered together next, a ring of 0.5mm diameter solder resting on the slight lip between the two components. Although this should have been relatively easy to solder, the great mass of the saddle made it much more difficult than expected, with a lot of heat directed into the hole at the top and rather less to the chimney neck to get both parts up to temperature.
The next stage was to bore the 2.5o taper in the bore and the 1.25o taper to the outside, both jobs done with the compound slide set to the relevant angle and with the assembly mounted on the same soft jaws. Finally, a turned section was formed at the top to take the chimney cap. Sorry, no picture of that. I didn't have a piece of brass big enough to make the cap as a single piece, so used two pieces instead. This is the first piece silver-soldered to the top of the chimney. The second piece was made and this was soldered omn as well, but using a lower melting-point solder. Then the assembly was remounted onto the soft jaws, the o/d of the cap skimmed to size and the upper radius turned with a form tool.
The same form tool was used to create the underside form but, because it was a larger radius, I nibbled away at it freehand (winding both the carriage handle and the cross-slide handle at the same time) using a radius gauge as a reference. This is the chimney with all the turning finished although I will use a bit of filler to disguise the lower join. It just leaves the machining of the saddle to complete.
To machine the underside of the saddle, I modified one of my flycutters to take a tool that I can adjust to 5.1/4" diameter. I have milled a shallow 5/16"-wide slot, with one edge on the centreline, and made a couple of clamps and an adjuster to hold a piece of 5/16" square tool steel. The tool has to be ground as left-hand-cutting, of course. This was an opportunity to try out my new cross-slide and I created the setup while the slide was still on the bench, using packing to set the centre-height. Then I swapped the cross-slides over - a matter of two minutes work - and set the flycutter to 2.5/8" radius. Although it doesn't show, I'm holding the flycutter in a collet block and this block in the chuck otherwise I wouldn't be able to get the length of cut required.
The compound curves on the upper surface cannot be machined conventionally and this arrangement leaves the front-to-back dimension too short, as can be seen. So the answer is to fix another piece to the bottom and build it up. First I cut a square from 20swg brass sheet, bored a 1.1/4" hole in it, put a bend in it and then clamped it to the bottom using the petticoat to get it tight.
Then it was rounded off freehand until it sat nicely on the smokebox. It's not a perfect circle because it would foul the rivets. Once happy with that, I drilled a couple of holes in the baseplate for 8BA fixing screws, spotted them through to the chimney, then set up the angle table to drill and tap the matching holes.
A pair of countersunk brass screws were used to fix the two together, the Hoffman roller being used to keep things in line whilst tightening. Finally, a load of high-temperature gunk was smeared all round the base and left for two days to cure. Then it was shaped with emery cloth and some light filing to create the finished curves. It is actually a lot smoother than it looks because of how the light reflects but this chimney is going to be painted, anyway, so the primer will hide any tiny blemishes prior to painting. The filler is supposed to withstand over 500 degrees centigrade, so should be suitable for this.
  3. Regulator  
Don Young does not provide details of the regulator, only the backhead fittings and a note to "use standard LBSC internals" or words to that effect. The same goes for injectors. I have made mine by modifying a 1/2" ceramic tap valve and mounting the whole thing in a tube. The big advantage here is that, if anything goes wrong with the regulator, I can carry a complete spare regulator assembly and change it in a very short space of time. The main controlling factor was how small I could get the maximum diameter of the valve without it falling to pieces. That turned out to be 18mm. To get things rolling, here is a tap valve disassembled to its component parts alongside another one. With the body devoid of parts, a close-fitting brass bung was made to fit in the lower part of the valve to protect it from distortion when clamping in the chuck. Then the whole of the outside was reduced to a few thou under 18mm. The top end was then reduced to 13.5mm to make a close fit to the bore of standard 15mm plumbing tube.
The valve was then reassembled but without the retaining circlip on the spindle; it's not needed and also it fouls the bore of the tube. The outer ceramic disc has a pair of lugs that locate in two splines in the bore but the inner one is free to rotate and can be set to operate clockwise or anti-clockwise depending on how the cruciform drive is set. The operating rod is set within the tube and fixes to the end of the valve spindle using the existing M4 thread. The steam tube delivers steam to the wet header and is comprised of three parts. The front section has a pair of "O" rings that seal within the wet header bush. To assist with assembly, there is a 15 degree chamfer on the front and the back end is bored to suit the outside diameter of the feed tube.
The tube itself is made from an offcut of the flue tubes and is silver-soldered into the back of the front section and into the supporting rear section. This a simple bronze bush turned to the same outside diameter as the valve. The valve presses up against this and creates a seal, separating it from the steam in the boiler space. A normal wet header bush would be quite short and just have a thread for the steam tube. This one is longer to accomodate the steam tube with it's "O" rings. Most of the work was done in a single operation prior to parting off. There is a 3/32" long stand-off ahead of the wet header mounting flange.
The bush was completed by reversing in the chuck, machining a recess for an "O" ring and another one for a locating spigot. The "back-of-a-fag-packet" sketch shows it better than I can explain. At the other end, a backhead bush had to be made that could pass the 18mm diameter valve through. This meant that the outside diameter was quite a bit over-scale at 1.330" diameter but, once painted, should be almost unnoticeable against the backhead. I was a bit limited for material to make this and used an offcut of bronze. Over on the mill, four 7BA holes were drilled and tapped in the flange for mounting the regulator bush.
The regulator bush was made the other way round, turning the maximum diameter first, then drilling and reaming the 5mm hole for the regulator spindle and the 9mm hole for the packing gland. Holding the flange in soft jaws, the body was turned to 22.0mm and a short spigot turned to fit the bore of the 15mm tube. On the mill, four 7BA clearance holes were drilled and a further two 7BA holes drilled and tapped for fixing the packing gland, then I siver-soldered the steam delivery tube. After that, I also soldered the regulator tube to the regulator bush.
The main body of the regulator is really only a thick-walled tube to support the steam pipe at the front and the valve body at the back. Squeezing the two sections together compresses the seal between them so all that is needed is a way to get steam to the inlet ports of the valve. A 3/16" wide undercut about 1/8" deep in a block of bronze is good enough for this and a collector pipe is screwed into the top to reduce the chance of priming. I've made the block from some hexagon bronze bar which I had in stock and one of the flats came in useful for fixing the support bracket to. It is important that the overall length of the assembly is accurate because tightening down the regulator bush has to compress the "O" ring in the backhead bush as well as squeezing the sealing ring in the valve. A simple job to face the tube to length, except that I can't hold the spindle tube in the lathe chuck to face it off because the flange is too big! Luckily, the collet block came to the rescue.
I can't clamp it up until the boiler is finished but this next picture shows how the regulator body sits within the dome bush and supports the steam tube and the valve body with it's spindle tube. Having the collector tube offset to the back has another advantage. Wilf cleverly suggested putting a large filler cap in the top of the inner steam dome for ease of filling the boiler so I shall make a feeder tube that sits below and forward of the steam collector. I had planned to fit a collar to the spindle tube and then fix the tube to the valve body with a couple of small screws but, in the end, I decided to solder it direct to the body with silver-bearing soft solder. All the parts are either copper or bronze except for the valve body which is brass and if this fails it will be easy to replace, The soft solder will be fine because the boiler temperature can never exceed the melting point of the solder. The operating spindle was made from 5mm diameter stainless steel rod, a 5/16" x 40 thread has been tapped into the end of the steam tube and an extraction tool made to aid future disassembly.
  4. Steam Manifold  
I have made the manifold as an assembly of eleven parts, all turned from Colphos bronze and soldered together with 1/2mm diameter silver solder wire. I started by turning the base of the main stem from 5/8" diameter material and threading it 3/8" x 40tpi to fit the manifold bush on top of the boiler. It was then screwed into a mandrel and all the other operations done in sequence, the first of these being to mill the square upper section to size.
The front and back centre ports were made as a single piece, turned down to 1/4" diameter and then drilled and tapped their respective sizes. A 1/4" diameter hole was drilled through the block and the front and back ports soldered in. Next, the two arms were turned, along with the outer valve stems and two half-way ports which are screwed into the crosspipes. These parts were also soldered together. Meanwhile, the centre block has been cross-drilled and counterbored ready for the crosspipes. It was quite fiddly getting everything aligned but screwing the taps back in helped enormously.
Lots more flux, including on existig joints, and the main body parts are joined together. With it all cleaned up, the single outlet on the top left arm had to be drilled and tapped. It was getting a little more difficult to hold in the vice, multiple packing pieces needed for the job.
The two outlets for the injectors neede to be set at about 35 degrees so, for me, the easiest way to hole the work was on the tilting table. The last few outlets were soldered in and this is how it looks after cleaning up. Just the valve assemblies to make for the outer ends and a dummy whistle for the top and this is complete.
  5. Firehole Doors  
There's not much to say about these, other than I've redesigned the backplate to make it fit to the extra stays that I put in the backhead. The two bosses are silver-soldered to the tails of the plate and the door runners are temporarily fixed with nuts and bolts The original design has the doors running on the outside of the door bars and lipped over the back but, because of space constraints, I've made mine to run inside the bars in channels. The doors are solid at the moment but I might hollow them out, more like the protoytpe. The linkages are cut from 16 swg mild steel sheet. This is the assembled mechanism using 3/32" diameter rivets for pivots. The screws that fix to the doors can be locked by a stud from the other side. Not very interesting but another job ticked off.
  6. Forward Clacks  
The boiler clacks are quite prominent because they have a fancy spacer between the valve and the pipe flange. I made all the parts for these assemblies from phosphor bronze, starting with the two main body parts. These are just straightforward turnings that get silver-soldered together. Previous experience has shown me that they never line up properly when assembled in place so, this time, I made sure I had a means of tightening them into the clack bushes before soldering. After screwing into a stub mandrel, the two branch pieces were drilled 4.3mm diameter for about 20 thou, followed by drilling through with a 4mm drill. A hexagon shape was formed in the ends by pushing in a cut-off Allen key with the end ground flat and square , then forcing deeper in the bench vice. This was followed by turning the O/D with a radius tool. I was able to remove the parts from the mandrel without damage.
The branch pieces were then screwed tightly into the bushes, complete with a gasket washer, and the top marked with a line. They were also noted as left or right. Having the hexagon for an Allen key really pays off in this situation. The four bolt holes in the body were drilled next, a four-jaw self-centering chuck proving ideal for holding the work in this operation.
I made the two spacer pieces and the two flanges next so that I could drill the bolt holes while the 4-jaw chuck was still mounted on the mill. The drawing says to make the spacers 1/4" wide but this looks too chunky to me and I have made mine 3/16" thick. The grooves were cut with a 4mm ball-nosed endmill and the outer radii formed with files, although they could do with a bit more work. The flanges are 3/32" thick, the same as the flange on the body. Then it was the main body, drilling and counter-boring the side hole for the branch piece to be soldered into. A pair of 10BA threaded studs were screwed into adjacent holes and rested on the vice jaw for alignment purposes. The two parts of each valve were joined together using a ring of 0.5mm silver-solder wire on the stem of the branch. The work was held in an engineers clamp so that heat could be applied from below and avoid directly heating the solder. Correction fluid has been painted onto the threads to protect them from stray solder.
This is the collection of parts needed to make a single clack, with an assembled one to the left. After cleaning up and assembling the various parts, they were fixed to their respective clack bushes using the same gasket washer as before. Nice and tight, and perfectly aligned. The body is a bit too long compared to the prototype but this is one of those situations where things won't scale properly. If the clack valve was scale size on the outside, the inside would be too small to let enough water into the boiler.
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