The next job was to work out exactly what bushes were needed on the boiler. The majority are just small 3/8" diameter bushes tapped 1/4"x40 (for boiler fittings and the two longitudinal stays) and I needed ten of these. I chose to fit bushes for the longitudinal stays to screw into rather than tap directly into the backhead and smokebox tubeplate as copper is dreadful stuff to tap and it's easy to strip the threads if you are not careful. On the subject of longitudinal stays, there is some doubt as to whether these actually do anything at all. The backhead and smokebox tubeplates are pretty well supported by the tubes, bushes etc. and the actual area covered by the stays is very small. However, we need some means of getting steam from the cab to the blower jet so we still need a hollow stay anyway so we may as well fit the solid one as well. I have thought of making both stays hollow as the second one may be useful for something (perhaps I could connect a manometer to the cab end for measuring the smokebox vacuum?).
As well as two bushes on the front of the barrel for boiler feeds I have also allowed two more bushes at the bottom of the backhead for injector feeds if necessary. I have also allowed a bush on the backhead for a blow down valve. It would be nice to have fitted one at the bottom of the throatplate as this is the lowest point of the boiler but I don't think it will be possible to get at it to operate it. I may fit a bush here anyway just in case. It can always be fitted with just a screwed plug for washing out the boiler now and again. The top fitting for the water gauge will have to screw into a special boss on the top of the backhead to give a decent length for the gauge glass.
The regulator will probably be the usual screw down type in a tube similar to Black Five so the backhead bush for this has to be large enough to take the tube for this. The steam pipe connection in the smokebox from the regulator will use an O ring for the seal into the bush on the tubeplate rather than the screwed connections usually used. Much simpler I think.
The remaining bushes are two 3/8"x32 for the safety valves, a plain drilled bush for the steam turret, and a 1" diameter plain bush for the dome. This is really only to allow the steam collecting pipe to be screwed into the top of the regulator and will carry just a plain flat cover plate.
The small boiler bushes were turned up from phosphor bronze bar and the larger ones (regulator, dome, and turret bushes) from gunmetal as I didn't have ordinary bronze big enough for those. The bar was turned down to a suitable diameter to fit the holes in the boiler and then parted off to give a 'top hat' shaped blank. The blanks were then reversed and held in a collet where possible, faced off and then drilled and tapped where necessary. The threads were not tapped fully but just started with a taper tap and will be tapped all the way through after soldering into the boiler shell etc. This avoids the possibility of the threads getting burnt and damaged during the soldering operation.
The bushes for the backhead and smokebox tubeplate were soldered in using silverflo 24 as it's easy to get these small assemblies hot enough to use this. One thing I noticed was that the surface of the regulator bush blistered in places, obviously due to the high temperature. This had been made from the same gunmetal bar as the valve chest for the middle cylinder which had also suffered when soldering with the silverflo 24. If I use any more of this for items requiring soldering I'll try and stick to lower melting point solders as the gunmetal certainly doesn't seem to like a lot of heat.
Bushes fitted to backhead and smokebox tubeplate
The next job was to drill the boiler barrel to take the bushes in that. I did this in the micro mill using a suitable set up to hold the barrel firmly. The smokebox tubeplate was pushed into the front of the barrel to give extra support when drilling the two holes for the boiler feeds. Similarly the backhead was used when drilling the holes for the safety valve and turret bushes.I found the best tool to drill the holes with was a centre drill (slocombe) as these cut well without snatching. It's very difficult to drill thin material, especially copper, with ordinary drills as they tend to grab and it's so easy to ruin the job. For the larger holes for the dome and safety valve bushes, the centre drill was used to drill a pilot hole and then the holes were carefully opened out by filing.
Drilling holes in the boiler barrel
I had already decided to fit the smokebox tubeplate at this stage so this was soldered in at the same time as the two boiler feed bushes using 440 silver solder. I know it's usual to solder the tubeplate at the same time as the tubes but I thought it would be easier to do it now rather than do the whole job in one go later. A bit of a jig was made to support the tubeplate in the correct position in the barrel as I thought this would be simpler than try rivetting the tubeplate in position. Unfortunately, after soldering I noticed that the tubeplate had rotated slightly so the tube holes are not quite level. Not a problem really but annoying just the same. Still, I can't do anything about it now!
The dome bush was then soldered in, again with 440, and finally the safety valve bushes and the turret bush. Great care was taken to get the safety valve bushes level so that the valves will be vertical when fitted. Nothing would look worse that the valves leaning in different directions!
All the boiler bushes fitted
There's not much more I can do to the boiler at this stage as it needs to be inspected before the firebox/tube assembly is fitted. Apparently the new boiler regulations require this so I've arranged to take the boiler to the 2.5" meeting at Chesterfield on October 1st so that Steve Eaton ( the boiler tester for the Association ) can give it the once over. If all's ok I can press on and get it finished. The one thing I am worried about is the soldering of the firebox stays as I think it is going to be well nigh impossible to silver solder the ends of the stays inside the firebox due to it being so narrow. It might be possible using Oxy-Acetalyne but I don't have access to the equipment. I am hoping it is still possible to use Comsol for caulking. What we need is a silver solder that melts at about 400 degrees C !
I am hoping to get the boiler for the A1 to a similar stage so that I can take that to Chesterfield as well. That will give me plenty to go at over the winter then.
Not much done to Helen over the weekend as I've been busy sorting out the junk under my carport/work area so that I can put a bench in there. I can then do any really noisy jobs such as sawing and hammering outside but still be under cover. I've also made a proper brazing hearth from some old Dexion angle and steel shelving. I knew it would come in useful one day!
I did manage to have a trial assembly of the firebox and tubes into the boiler shell. Apart from having to bend the tops of the firebox stays to match the inside curve of the boiler shell it all fitted together very well. I thought I may as well cut the hole in the backhead for the firehole tube while I was at it so I carefully measured it's position from the edges of the backhead and then drilled and bored the hole in the lathe. Fortunately when I tried the backhead in position the hole was pretty well spot on. The flange on the backhead needs trimming a bit as its too wide in places and also a little bit needs taking out to clear the turret bush. I also finally trimmed the bottom edge of the firebox to the correct shape after marking it off from the bottom of the boiler shell.
She's looking more like a loco every day!
One thing I have realised is that I forgot to cut off the front top corners of the horns for the third axle before I fitted them to the frames. This is necessary to clear the bottom sloping edge of the firebox wrapper so at the moment the boiler sits too far forward in the frames by about 1/4". I will have to remedy this some time in the future, probably by using a cut off disc in the dremel.
I've had some good news from Steve Eaton, the Association boiler tester. He is quite happy with soft solder caulking for the firebox stays so that will make the job of soldering the stays much easier. Apparently there are some clubs who do not like it however and insist on all the stays being silver soldered. Personally, I don't see the problem with using Comsol so long as you don't let the water level in the boiler get too low. The worst that can happen is that the solder on the top row of stays may melt and cause a leak into the firebox but if the threads on the stays are a good fit in the wrappers and proper nuts are used inside the firebox then there will be no loss of strength to the boiler. There must be hundreds of boilers around with soft solder caulking that are still in use, especially 2-1/2" gauge ones.
I've had a bit of a break from Helen while I worked on the boiler for the A1 but that's now ready for inspection so work on Helen can continue.
I've done one or two minor jobs that needed attention i.e. I've cut off the top corners of the axlebox horns on the third axle using a cutting disc in the Dremel to allow the boiler to sit further back and I've also fitted a bush in the boiler throatplate for a washout plug. It may be possible to fit a blowdown valve here if I can find a way of operating it from outside the frames. Looking at the position it would fall into, I may be able to drill a hole in the frames behind the driving wheel and access the valve with a tool inserted between the wheel spokes.I've still heard nothing about the bogie wheel castings from the Association so I may try another source for these.
The next main item on the agenda is the outside cylinders and I'm working on those now. The method of construction is pretty much the same as for the inside cylinder so I won't go into great detail about making these. I'll just post a few pics as I go along and mention any differences.
Machining proceeded pretty much as for the inside cylinder but this time I bored out the valvechests to the finished size of 7/16" diameter before soldering them to the cylinders rather than finish them later. This would make the final machining of the completed 'castings' a bit easier leaving only the cylinder bore to machine to final size. I reasoned that any slight distortion of the valvechest bore caused by the soldering would be removed by the lapping as done for the inside valvechest.
Machining the cylinders
Ports machined and the jig for soldering valve chest to cylinder
Embryo cylinders after soldering
The mounting lugs for the cylinders are a bit simpler than those for the inside cylinder as they only have to fit one side. Four blanks were cut from 1/4" brass, soldered together and machined as one block. The curve to fit the cylinder was machined in the lathe and the recess to clear the exhaust manifold milled in the vertical slide. The blanks were left slightly oversize to allow for final machining later.
Machining the blanks for the cylinder mounting lugs
Slot milled to clear the exhaust manifold
Mounting lugs after separation
The exhaust manifolds were again machined from 1/2" x 3/8" brass bar. However, this time the exhaust outlet is in the centre rather than at one end so an outlet boss was turned from brass bar and soldered in with 440. The boss was left long so that it could be machined to length at the same time as the mounting lugs. A recess was machined into the chassis side of the boss to take an 'O' ring for sealing the exhaust pipe which will just push fit into the boss.
Exhaust manifold blanks before milling
I decided to solder on the exhaust manifolds at this point using Easyflo as I thought it would then be easier to fit the mounting lugs with a solid assembly to work to. The solder would melt again when the lugs etc were soldered but so long as everything was clamped up solid there shouldn't be a problem. The lugs were then filed until they were a good fit on the exhaust manifold and the cylinder.
As mentioned in earlier pages I had decided to route the steam pipes under the running boards rather than have the normal external ones to avoid having to make fiddly connections inside the smokebox. After some thought I settled on using another brass manifold on top of the steam chest into which would screw an inlet stub projecting through the frames into the main steam distribution manifold under the smokebox saddle. The stubs will carry 'O' rings to seal the joint into the main manifold. This means the cylinders can be removed without having to undo the usual fiddly screwed connections, both the inlet and exhaust connections being push fit. The cylinder manifold was machined from 1/2" x 3/8" brass bar again and the bottom profiled so that it sits half on the valve chest and half on the exhaust manifold. The inside was then milled out to form the steam passage. I thought it best not to drill for the inlet stub at this point so that it's final position could be checked from the job.
Milling out the inlet block
Next was the big solder up and the point where it could all go horribly wrong! I used the same jig to hold the mounting lugs in place as I used to solder the valve chest to the cylinder and the inlet manifold was clamped in place with an old G clamp. To be honest, clamping the bits together like this is asking for trouble in case something moves and it's a much better idea to fasten everything together with a few brass screws. I went ahead anyway and soldered the lot up without any major disasters. I did have an 'Oh Bugger' moment with the first cylinder when I was a bit over generous with the Easyflo and thought I had soldered one of the clamps to the cylinder! I carefully heated the clamp to remove it but fortunately it was only stuck on by the residue flux. It has left a lump of solder though which will have to be filed off. The second time I was more careful!
Inspection of the cylinders after pickling showed all the joints to be sound and everything in the right place - sigh of relief! Hopefully the worst is over.
The cylinder 'castings' after final soldering
There are a couple more pieces to fit to the cylinders. These are the little 'V' shaped filling in pieces on the outside ends of the cylinders to fill the gap between the cylinder and the cladding but I'll make those later and probably solder them on with Comsol as they are purely cosmetic.
Now begins the process of final machining but it should all be pretty straightforward.
The first job was to machine the mounting lugs and the exhaust stub to length and I decided to try flycutting for this as the area to machine is quite large. It's not a machining method that I've used much but it turned out to be a very easy job - much easier than using an endmill and having to make several passes at each cut. It also means that the surfaces are all nice and level.
Flycutting the mounting lugs and exhaust stub to length
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