3

The inside connecting rod was tackled next and machined from 1/4" mild steel flat. The edges were milled in the lathe like the coupling rods and the small end rounded by filing using hardened steel buttons as a guide. By this time I had acquired some woodruff cutters and the sides of the rod were fluted using one of these with the corners rounded off to give the correct profile to the bottom and ends of the flutes. The big end shells and the small end bush were machined from phosphor bronze bar. Custom made 5BA bolts were turned to bolt the big end cap to the connecting rod. These were made a good fit through reamed holes in the cap and the rod thus ensuring accurate alignment on assembly.

Completed inside connecting rod

The complete middle cylinder was fitted into place and I breathed a sigh of relief when everything seemed to line up ok and the crank axle still went round when the big end bolts were tightened up!

Middle cylinder and connecting rod fitted in place

A return was then made to the outside cylinders. The valve chests were cleaned up and the front bosses machined to take the extended valve spindle and O ring seal. New steam inlet stubs had to be turned as the layout of the steam manifold is different for the three cylinder version. The steam manifold itself was turned from bronze bar and the oil pipe connection, middle cylinder steam connection, and the main steam inlet connection were turned separately and silver soldered in. I had a slight problem here as I had turned the main steam connection from a piece of aluminium bronze and this didn't seem to want to take the silver solder properly. I eventually ran some soft solder over the joint to make sure it wouldn't leak. I learnt afterwards that some ordinary salt should be added to the flux mixture when soldering aluminium bronze to help clean the metal. I think this idea of fitting all the steam connections with O ring seals and push fitting them together is a much better idea than using fiddly bits of threaded pipe that are a nightmare to put together and take apart again! I'm sure that O rings could be used instead of olives on pipe connections.

Outer cylinders fitted temporarily to check fitting of steam manifold

New steam manifold

I thought I'd fit the saddle next as I knew that part of the rear base had to be removed to clear the middle cylinder. I wasn't very chuffed when I realised just how much had to be removed! Also a recess had to be filed in the front of the saddle to clear the steam inlet for the manifold. It was a bit of a tight squeeze to get it to fit.

Fitting the saddle

At this point I thought it was time to finish the chassis off by adding the rear subframe and trailing axle. Unfortunately I had another attack of 'scale-itus' and decided to fit a proper Cartazzi trailing axle. I had previously obtained a set of Don Young's Locomotives Large and Small (an excellent magazine which ceased publication on Don's untimely death) and one of the locos described therein was Doncaster, a 5" gauge A1/A3. The loco is a highly detailed and accurate model which was designed using the original works drawings. To make life easier I just copied the 5" version of the horns and axleboxes at half the original size. In fact If I were starting again with this project I think I would have used this design redrawn to 2 1/2" gauge. Too late now though!

The subframes are basically the same as the version in Model Engineer but the horn slots are slightly larger to accept the Cartazzi horns. They were bent up cold from 3/32" mild steel but I would recommend anyone to heat the steel before bending as it's quite difficult to get nice sharp bends when bending the steel cold. It would also be better not to cut out the horn slots until the frames had been bent. Anyway they turned out ok the way I did it.

Obviously there are no castings available for the Cartazzi horns so the only alternative was to fabricate them. I used mild steel but could have used brass I suppose. Each horn was built up in two pieces silver soldered together. The main piece consists of the flange that bolts to the frame and has the ribs milled into it. This was machined from 3/8" square. The actual angled bearing face is a piece of 1/16" flat silver soldered on after the angle (17 degrees) had been milled on the ribs. The horns are fastened to the frames with 8 10BA nuts and bolts. The work involved was very fiddly and time consuming but the result was well worth it.

The built-up Cartazzi horns

Axleboxes and spring plates fitted

That about brings construction so far up to date. I'm working on Helen Longish at the moment but will try to progress the Scotsman at the same time. Watch this space!

25/08/2006

It's been a while since I did any work on the A1 due to working flat out on Helen. However, as mentioned in the Helen write up, I want to take Helen's boiler and this one to Chesterfield on October 1st for a preliminary inspection prior to installing the fireboxes etc into the boiler shells. So I have started work on this boiler as well.

The A1 boiler, although a much easier shape than Helen's, is quite a complicated affair. By easier shape I mean the sides of the firebox and the outer wrapper are straight with no reverse curves like Helen's so forming the boiler plates and wrappers should be easier. The job is made a little more difficult because the throatplate and backhead are both sloping rather than vertical which means the outer wrappers have to be shaped to suit. The really complicated bit is the dreaded combustion chamber! Builders tend to avoid combustion chamber fireboxes like the plague as they can be difficult to make and great care has to be taken to ensure there are no leaks before the firebox is fitted into the boiler shell. It would be very difficult to re-solder any joints once the firebox is in situ, although any slight leaks could easily be sealed with Comsol.

The A1 combustion chamber involves quite a lot of work as it is also fitted with vertical water tubes to further increase the heating surface. Paul Wiese and Derek Collin do say that the combustion chamber could be omitted and the length and diameter of the fire tubes increased to compensate but I think a combustion chamber does make a big difference to the steaming of the boiler and is worth fitting despite the extra work. Steve Eaton has an A3 built to this design and it goes like the clappers and the boiler seems very easy to fire and produces plenty of steam.

I had previously spent quite a bit of time redrawing the boiler with CAD and producing templates for the flanging plates and wrappers. Because the plates all slope the top edges of the plates are at an angle to the front surface and the top edges of the flanging plates were chamfered to take this into account. The amount of chamfer was worked out by taking dimensions from the boiler drawings.

The templates were then printed out and then laminated. This gives a good strong plastic template which will resist oil etc much better than thick paper which I have used in the past. After cutting out, the templates were stuck to the metal with double sided tape and used as a cutting guide. I decided to use 5/16" steel plate for these formers rather than the 1/8" steel/wood combination I used for Helen. It's a lot more work cutting the plates out but solid plates do give better results. Also I'll be able to lend the formers out to anyone who wants to build a similar boiler.

The backhead was tackled first and was flanged up with no trouble at all from 3/32" copper plate.

Backhead template stuck to the metal ready for cutting out

Flanged backhead with the former used

Next up was the throatplate. This is a bit more tricky to make as it is a proper double flanged job. I flanged the sides first and the radius to fit the boiler second but I think it may be easier to do the radiused flange first. After flanging the sides the plate was turned over to do the radius as obviously the flanges are in opposite directions. Ideally you want two formers to do this and clamp the plate between the two otherwise the plate will distort and finish up all shapes. I didn't fancy chopping another former from 5/16" steel so I made do with a block of hardwood shaped to fit which did the job admirably and was a lot easier to cut! The two 'ears' at the top of the plate need to be trimmed to fit between the boiler barrel and the outer wrapper.

Flanged throatplate and former

The shape of the outer wrapper had been carefully worked out from the drawings to take into account the sloping plates and this was cut from 16swg copper using a laminated template as for the formers. It was then annealed and bent around a piece of tube to give the top radius. As mentioned before, the sides are straight which makes the forming of the wrapper very simple. After cutting out, a centreline was scribed on the top of the wrapper to help alignment when fitting to the barrel. A centreline had also been scribed on top of the tube used for forming the wrapper and the two were aligned when the wrapper was clamped to the tube for bending. This ensures that the wrapper will be true after bending.

Template for outer wrapper

Forming the wrapper around a piece of tube

28/08/2006

The wrapper and throatplate were assembled to the barrel using 10BA nuts and bolts and when I was happy with the fits and alignment, these were replaced with 1/16" rivets. The throatplate was a little tricky to get to fit properly as the top 'ears' have to be filed to a fine taper to fit between the wrapper and barrel where the two meet. The whole lot was then silver soldered together with Silverflo 24. I struggled a bit here as I used too small a burner at first and I didn't get the job hot enough quickly enough and the flux went off before I could finish all the joints. Also the burner used ( Sievert 2943) kept blowing out. I abandoned this attempt and dumped the assembly in the pickle bath ready for another go. This time I used the biggest nozzle I had ( 2944) and the job was a breeze with this burner. The problem seems to be that the flux has a very short life and if the burner is too small it becomes exhausted before the joints are up to temperature . If in doubt, use a bigger one! In his article on building the 2-1/2" Black Five, Martin Evans says a 2943 burner should be ample for that boiler but I think you would struggle unless everything was surrounded by coke or similar. I prefer to keep the job open so that you can see better and there's less chance of the burner going out through lack of air. The 2943 burner seems fine for all the other jobs on the boilers.

Throatplate joints after soldering

Boiler shell on the frames

When the shell was tried in position on the frames I noticed that the barrel sits on the tops of the curved parts of the frames over the wheels so these may have to be chamfered on the inside edges to give more clearance.

Nearly a full day was spent cutting the firebox formers out of the 5/16" steel and flanging the plates up from 13swg copper. All good exercise! The tricky one was the tubeplate for the end of the combustion chamber as the corners are quite small radii. The smokebox tubeplate was flanged up using the former made for Helen as the barrel is the same diameter.

Firebox/combustion chamber plates and formers plus smokebox tubeplate

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