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 B1 - Formers, Materials etc
  1. Barrel and Ring  
The barrel has been machined to length by holding in the bore and supporting the other end in a steady. My steady wasn't large enough to use the rollers so I set some PTFE pads on the outboard ends of the arms and then reversed them. With a drop of lubricating oil, they worked fine. This isn't locked down yet but it shows the pad in place Although it had been sawn reasonably square and didn't really need to be cleaned up, I faced about 20 thou off the first end. However, for some unknown reason, I ordered an overlong piece and decided to part the surplus off. The ring will come in handy one day. I cheated, though, I only parted about three-quarters of the way through then hacksawed the last bit before finishing the face with the parting tool.
The barrel ring was made using the lump of bronze that I had originally trepanned from the Britannia front ring. Once again, I started by trepanning out the middle, going half-way through then reversing the billet. Rather than just turning the outside into swarf, I cut a thin ring from the outside as well. I don't have a use for it yet but oneday... These are the three billets that were produced, the middle ring the one that is needed. I hate wasting material of this value.
The outside diameter and one face were machined square to each other, then the billet was loaded to soft jaws and practically all the machining done in a single operation; two bores, the front spigot and the o/d with it's radius. The radius tool is just in the picture. The offcut from the tube was used as a gauge. That left nearly 1/8" to come off the back and the spigot for the smokebox backplate to be machined. A register was turned on the outside of the soft jaws and the work held in the front bore. Then it was faced to length and the spigot turned to finished size. Most of the machining was done at about 350 rpm and using the feedbox whenever I could. This is the barrel with the smokebox ring fitted to the end. A few countersunk brass screws will be used to hold it all together and these will be concealed beneath the cleading.
  2. Formers  
I've now made a start on the rest of the items needed to construct the boiler and the first things I made were some formers for flanging the various end plates. I have made these from 20mm MDF as I have used this before and found the material works a treat. The front and back firebox plates are the same size and have a large radius at the top corners. I drilled a 5/16" diameter hole at the origins of the two circles and used these as pivot points on the rotary table. I also machined a small radius to the outer edges using a router cutter so that I dont end up with a sharp corner inside the flanges. Two other formers were made at this time, one for the front tube plate and one for the backhead but I will make the one for the throatplate once I see get the outer wrapper shaped. The second hole in each former gets used as a means of stopping the work rotating about the pivot by clamping to a tee-slot.
I decided to make the front tubeplate first using a piece of 3mm copper. I roughly cut out the shape, then placed it between the former and a solid backing plate and held it in a bench vice. Then it was a case of some firm tapping followed by annealing at red heat and plunging into cold water. The plunge isn't strictly neccessary as the copper goes soft anyway but it flakes off any scale and speeds the job up. It took two annealings to get this far. I was cutting off surplus waste with a hacksaw as I went but it was getting more difficult to keep the shape the further round it went so I used the lathe to trim it down when I was about ninety percent of the way there.
Once I had the copper firmly on the former all the way round, I then skimmed the O/D and faced the back. The only way I could find to hold the tubeplate was with my 4-jaw SC chuck because the 3-jaw wouldn't go down far enough. I turned it to about 10 thou oversize, then trimmed it to length using a left-hand tool. The barrel was then returned to the lathe and mounted in the fixed steady so that I could bore it to fit the tubeplate. It needed to be 1.1/2" deep to allow the plate to sit at the correct depth. I only use those super-sharp polished carbide tips for turning copper because ordinary tips tend to be useless with soft materials.
By having a small shoulder, it also means I dont have to use any fixings to hold the tubeplate in place at soldering time, gravity does the job for me. At the moment, it's a nice sliding fit but it will probably become distorted during the various operations between now and then so will needs tweaking at the time. Then it was time to put the holes in and this was done on the mill using the DRO to locate them all. I used an 8mm drill to start with, then followed with a series of slot drills to get the holes to size. The 10mm tube holes needed the reamer run through and the superheater tube holes were bored but the three remaining holes were just left at whatever as the bushes will be turned to fit. Offcuts of tube were used as gauges.
  3. Endplates  
More of the boiler parts have now been made including the firebox endplates and the backhead. These have all been melded around their respective formers and the workshop became quite hot with all the annealing that was needed. In case anyone has never annealed a piece of copper and was wondering how hot to get it, it's this hot! Because the formers won't be needed again, they were used to support the work while the edges of the flanges were machined to size. The copper is still very soft at this time and will bend away from the cutter quite easily. I used a 1/4" diameter end mill to trim the edges, going round in a clockwise direction (climb-milling) to give the material maximum support.
The former was also used as support when I milled the endplates to length. The firebox tubeplate was drilled in similar fashion to the front tube plate, the rear tubeplate has had the firehole bored to size and the backhead has been fashiond around another MDF former. The tubes were expanded at the back end by about ten thou, then skimmed back to just under 10mm so that there is a tiny shoulder for the tubes to rest on when silver-soldering. Nothing is needed at the front because the front tubeplate will rest on the lip in the barrel.
Some 6BA bronze screws were made and these have been used to fix the wrapper to the end plates. I don't like rivets for this because they don't holed the work firmly enough. Also completed was the holes in the barrel for the forward clacks and the large steam-dome hole. The front tubeplate was used against the chuck jaws as a depth-stop and an MDF former bolted to a faceplate acted as the support for the other end. After drilling and reaming the two clack holes at plus and minus 90 degrees, the rotary table was set to zero and the big hole roughed out with a hole-saw before boring to size. Once this was complete, with the rotary table still set at zero degrees, a scriber was mounted in a drill chuck and dragged along the full length of the barrel. I didn't do this on the Britannia boiler and had alignment issues because of it.
  4. Throatplate  
The outer wrapper had a centreline scribed at the half-way point and was simply folded around the barrel, followed by bending back to form the waist and creating a nice fit around the backhead. Then it was on to the throatplate. This was the most difficult part to make because of the reversed double flanges and I cut the raw material a good one inch bigger all round than the suggested starting size. I also cut a packing piece for the front of the wrapper, clamped the backhead to the bench and temporarily assembled things to get a feel for the finished shape and size. The offcut of tube was used to mark where the barrel reaches to.
Learning from my experience with the Britannia boiler, I decided to get the side flanges fully-formed first and a piece of MDF was made into a former. I could have cut down the backhead former and used that but it was just as easy to make a new one. No pictures here, it was just simple folded-over sides. The former for the barrel flange was a little more complicated and a piece of oak kitchen worktop was used to make this, squared-up all round and milling out the middle to support the side flanges. The top was shaped using a 110mm hole saw. The first former was cut down to act as an internal support but allow the flange to be formed and the throatplate was placed in the former and the flaring at the top beaten into place. Some of the waste area was marked for removal and was cut out with the Abrafile before I started to form the barrel flange.
I found early on that the sides of the former would need support and a large clamp was used with the rest just held in a bench vice. I don't have any special hammers for copper-forming and a one-foot length of 1.1/2" diameter stainless steel was used instead because of the concave form. Between the many annealings, I kept returning to the mill to remove excess material because the further I went, the harder it got to keep the shape. This is the point that I decided to call a halt to the bashing and bring all the flange widths to size although the picture was taken after thinning the top wings.
So this is a trial assembly to see how well things fit and it's not too bad. The circular shape wasn't perfect, however so I decided to skim a little off the inside using a flycutter. I don't have any left-hand tools for the boring head so set up a right-hand one and ran the mill in reverse. This promply unscrewed the head from the mandrel so I had drill and tap a hole in the side to accomodate a locking grub screw. After that, I milled the diameter to a near-perfect fit. Once again, the former acted as a support for the soft copper and the opportunity was taken to scribe a centre-line through the workpiece.
A pair of fixing holes were drilled in the barrel flange and this was then rested on the barrel using a large vee-block to get everything in line and upright. The holes were transferred through to the barrel and a pair of 6BA holes tapped to take some bronze screws at soldering time. Another centreline was scribed on the underside of the barrel, diametrically opposite the top one. This enabled accurate alignment of the throatplate. Another fixing was made to hold the wrapper to the barrel and the assembly held together with clamps. I can now mark out a few more fixings knowing everything is square and correctly aligned. I won't make any fixings for the backhead yet, though, because things like the firehole ring and the foundation ring will determine the final position of that.
  5. Outer Wrapper  
Before going any further, I wanted to make sure that the firebox fitted as it should in the outer wrapper. With it resting on a piece of 1/4" square material, it seemed to fit as it should. The backhead was held loosely by the spring of the wrapper. Satisfied with that, I then set about cutting the wrapper and backhead to length. The throatplate is already to the size on the drawing and is square to the barrel so this was used to mark across to the other components. The wrapper was given a good, long soak in the pickle to clean it up for soldering and the three top bushes prepared.
With the wraper now to length, I was able to mark out and fit the two blowdown bushes each side at the bottom as well as the safety valve and manifold bushes on top. The top faces and the thread were painted with correction fluid , the outsides coated with flux and the holes in the wrapper fluxed as well. This last may seem unneccessary but I have had failures in the past for ommiting this step. I think it's about wetting the surface to break surface-tension. On the underside, the bushes protruded about 1/16" and solder rings were placed over these. I'm using 40% silver solder for all my bushes, which will all be fitted first, and 55% silver solder for everything else. More flux was added on top of the solder rings. A hearth was build from Celcon/Thermalite-style building blocks and the wrapper placed as shown. The bushes are kept in place by resting on the thin piece of block and the side blocks keep the wrapper upright but also enclosed to preserve heat. If the workpiece was out in the openm it would spend much of the time radiating the heat away again, wasting it. Lifting the wrapper in this manner allows me to apply heat from below to draw the solder through.
After a single heat-up, followed by gentle cooling and a spell in the pickle, I have a perfect set of joints with nice fillets on both sides. They may not be the prettiest and I've used more solder than needed on the manifold bush, a full ring of 1.0mm solder rather than a partial ring that I used on the other two. This shows the importance of good preparation, it's too easy to get complacent and then have to remake one or more joints. The two blowdown bushes were done one at a time and this is how it all looks with the backhead clamped in it's approximate position. .
  6. Dome Ring  
Looking for a piece of suitable material, a friend produced this nice lump of cored bronze that's just right for the job. I decided to turn the outside form first and also make the dome ring from the same material. The o/d is finished at 2.1/2" dia and the spigot at 2.1/4" to fit the bored hole in the barrel. Parting off was a little interesting, using a 1/16" parting blade sticking a loooong way out of the holder. Sawing off would have wasted too much material and this stuff ain't cheap! The dome bush was reversed in the chuck, given a light skim across the face and then bored out to 2" diameter, leaving a 1/8" thick ring at the bottom with a 1.1/4" diameter hole through it.
Moving to the mill, I cleared away some of the base to leave a pair of mounting lugs for the regulator mechanism. I also drilled and tapped a dozen 4BA holes holes in the bush and a matching set of clearance holes in the ring. I need a short length of 2" dia copper tube to silver-solder into the ring to form the inner steam dome. A pair of 4BA clearance holes were also drilled in the lugs. Don Young doesn't give any details about the regulator - use standard LBSC fittings, whatever they may be - so I'm going to use a "regulator in a tube" method. Although the assembly should be completely below the dome bush, I have relieved the front and back sections. The two lugs will provide a fixing point for some sort of cradle.
  7. Backhead  
It's impossible to make the gauge glass arrangement look anything like the prototype and still function properly and the backhead of the model only bears a passing resemblance to the full-sized "Calbourne", anyway. The upper bush is the one that causes the problems and DY drew up a flimsy bracket with a couple of bits of tube soldered together that looks awful. My effort doesn't look any better but is a fair bit stronger. To allow for replacement of the complete gauge glass assembly I made a bush from hexagon bronze, drilled and tapped 1/4" x 40 tpi the same as the fixed lower bush, and soldered a short length of 1/4" diameter thick-walled copper tube to it with 40% (high temp) silver solder. The backhead was clamped to an angle plate and a matching hole made with a 3/16" diameter slot drill. Then the upper bush assembly was set in the hole using a spacing gauge to set both height and orientation.
I've chosen hexagon material because I will be able to support the bush with a spanner when I tighten up the top fitting. The lower bush has also been soldered in with 40% solder, as will be the fitting-to-backhead joint. That way, I should have no problems when it comes to closing the boiler. Although it looks a bit silly at the moment, once the cab front is in place, it will blend into the background. The drawing shows the position of the upper bush suspended in mid-air.
This is the completed assembly set into the boiler. A small notch has been cut to allow the backhead to sit in the correct position but there is still plenty of flange available for soldering at final assembly. Following advice, I've also cut the inside part back flush with the inside of the backhead.
  8. Steam Dome  
I've redesigned the dome to suit my particular regulator arrangement. My steam collector tube will be a bit shorter and I won't need a gasket. A coverplate was made from a piece of the bronze and a piece of brass tube was parted off for the upper section. The first job was to turn the O/D to 2.500" diameter and machine a shallow spigot to locate the brass tube for soldering. The rest of the turning was done in soft jaws, much easier to hold the workpiece with these. First, they were machined to grip on the O/D with clearance for the spigot. For anyone unfamiliar with soft jaws, here they are being machined. One of the chuck key holes is identified with a mark and I only ever use that particular one when machining the jaws or loading the work. It compensates for any looseness in the scroll.
I didn't fancy trepanning out the whole billet on the first op but it was worth saving the ring on this next one. These toolposts are pretty flimsy affairs at this size so the G-clamp protects it against a dig-in which might break the tool holder lock. That came away fairly easily and I expect there will be a use for the ring somewhen in the future.
The front was turned to a bare 2" diameter to fit the dome bush, then a 3.5mm wide undercut was formed to take an "O" ring. If it snags, the centre will stop the work climbing out of the chuck and breaking the tool. After the picture was taken, the centre section was cored out to leave the coverplate 1/4" thick for the filler plug. This gives a little extra height for the steam collector tube. The holes for the mounting screws were drilled on the mill, as was the M14 x 1mm tapped hole. I have offset this to the front so that water doesn't pour down the steam collector which sits at the back. This is the plate resting on the dome bush.
The filler plug was made from 5/8" diameter phosphor bronze using a button die for the thread. The flats were milled by holding the workpiece in a hexagon collet block and rotating round in the milling vice, finishing at 12mm AF. The "O" ring collar was made from a piece of 1" dia brass, bored to fit the 5/8" dia PB and further bored to 3/4" diameter by 80 thou deep. The setup shows the clamp doing two jobs, holding the thread and acting as a depth-stop for the collar. Before silver-soldering the parts together, the thread of the plug and the reccess in the collar were both covered in correction fluid because it would be extremely difficult to clean up if the solder should run away. After that, the brass tube was soft-soldered to the top of the coverplate to act as the filler reservoir. These are the parts cleaned up and fitted with "O" rings, ready to assemble.
One of the guidance principles of the HSE is about restricting access by untrained personnel and many things require the use of a tool to access, adjust or remove, the thinking being that if you are able to use the tool, you probably know what you're doing. This bung requires the use of a tool to remove it, satisfying that requirement. It shouldn't be difficult to find a tool at the club. Here it is, mounted on the dome ring and looking very similar to the earlier version. The larger reservoir should make filling the boiler even easier. The thinner mounting ring is also better, allowing the screws to go in an extra thread or two.
  9. Next Item...