I haven't done much on Helen for the last week or so due to other things such as machining a new set of cylinders for my brother's Rob Roy. The original ones were very poorly machined but fortunately I managed to pick up a pair of unmachined cylinder castings off Ebay for a very reasonable price. I can salvage the end covers and valve chests and I'm going to make new slide valves from solid PTFE.
I've lengthened the driving arm on Helen's lubricator and arranged the operating link from the pump eccentric to run underneath the axles which makes it a lot easier to get at if necessary. This has approximately halved the output of the pump so we'll see how it goes. One problem with the lubricator showed up at the next steam test when one of the ball valves started leaking allowing steam to blow back into the lubricator. This was cured (I hope!) by stripping the pump assembly and fitting 'O' rings in the valves to act as a seat for the balls rather than the original metal seat. The 'O' rings were 3/16" outside diameter with 1/16" inside diameter and fitted perfectly. I know some people use this idea for water check valves etc.
I've also written an article on Helen's progress so far for the 2½" Gauge Association's journal 'Steam Chest' which should appear in the May issue.
I've now finished the Rob Roy cylinders (and a pair of connecting rods as well!) so it's back to Helen.
I've made a new operating rod for the lubricator as the original was only temporary and fitted all the proper bolts etc in the valve gear as I don't want to disturb the cylinders etc again until the finished loco is stripped for painting after steam trials. As promised, a more few photos of the work so far:
..............Spring drive to lubricator.................................Lubricator drive from water pump eccentric
..................................................View of cylinders and conjugated levers etc......................................Front view of chassis
Chassis and boiler shell in front of GA drawing
(Note bogie wheels 'borrowed' from the Flying Scotsman!)
I thought I'd tackle the smokebox saddle next as this is a simple fabrication from brass bar and sheet. Four pieces of bar were cut, the ends faced up in the lathe, and fastened together with 8BA brass screws to form the front and sides. The joints were then silver soldered. The base was then roughtly sawn to the correct height and soft soldered to a brass plate enabling the base to be bolted to the vertical slide for machining the radius for the curved flange with a boring bar.
Cutting the curved top of the base
The flange was then cut from 16swg brass sheet and bent around a suitable former. It was then held to the base with a couple of brass screws and finally silver soldered in place. The flange was then trimmed up with a file and a step machined on both sides of the base with an endmill to fit snugly between the frames. Various slots had to be filed in the front and sides to clear the steam pipes and the oil delivery pipe and then the mounting holes were spotted through from the frames. I must admit it seems a lot easier to fabricate saddles rather than use castings. There's a lot less machining involved!
Smokebox saddle fitted to frames
The original idea was to roll the smokebox up from brass sheet but as I haven't got around to making the bending rolls from the kit I bought last year, I've decided to use a piece of tube instead. Unfortunately the size I want is out of stock at our local supplier so that job will have to wait for a bit.
I thought it was about time that I made the proper eccentric rods for the valve gear now that the chassis has been tested and proved ok. The calculated length seems to be spot on so the new ones will be made from 1/8" gauge plate to the same dimensions as the temporary ones.
The eccentric rods are simple milling and filing jobs with a Peek bush fitted at the return crank end and a plain reamed hole for the expansion link pin. The rods will be retained on the return crank with a turned brass nut. I decided to flute the front of the rods using a small slitting saw to improve the appearance and it was also necessary to put a slight offset in the rods to line up with the expansion link.
Eccentric rods fitted
The last jobs remaining on the valve gear are pinning the return cranks to prevent them moving and making the reach rod from the reverser to the weighshaft.
I've been spending a bit of time drawing out the running boards and the side tanks. I've decided to fit a full length running board to each side made from 18swg brass which will be permanently bolted to the chassis. The side tanks will then be seperate assemblies which will simply bolt on top of the running boards making them easy to remove if necessary. The tanks will be the full width of the running boards which will mean the backs will have to be stepped in at the top to clear the boiler barrel. This will make the tanks a bit more complicated to make but will give the maximum water capacity possible. The base of the tanks will also be quite fiddly as they will have to have sealed cut-outs to clear the wheels and the expansion links which stick up slightly above the running boards.The tanks will also be much longer than shown on the original design, again to increase the capacity. Personally I think the tanks on the original design are far too short for the length of the loco and spoil the lines, although Hughes's Baltic tanks did have quite short tanks in real life.
I'll probably tackle the running boards and then complete the boiler before starting on the tanks. Once the boiler is finished I can at least steam the loco using an external water tank on the driving trolley! (That's another thing to start thinking about - building a driving trolley!)
The running boards are made from 18swg brass strip and I got our local supplier (Live Steam Models) to cut two 3 foot long strips to the correct width to save sawing them from a large sheet. They are quite a complicated shape and will have to be made in several sections. The longest section runs from the front of the smokebox saddle to the rear buffer beam and has two 'S' bends in it as it is at three different levels. I decided it would be easier to bend the strips to shape before cutting out the slots to clear the wheels and the expansion links and to make the job easier I made a simple jig to get the bends in the right place. This was just a piece of old kitchen worktop with pieces of tube screwed to it of the right diameter to form the bends. A couple of pieces of angle were also screwed to it to secure the strip in position and to ensure the strip was held vertical whilst it was bent. A template was printed out to show the outline of the edge of the running boards and to position the pieces of tube. The first bend was done with the brass strip in it's hard state but it proved to be quite springy and hard to form to the correct radius. Subsequent bends were done after annealing the brass by heating it to a dull red and allowing it to cool naturally. This made bending the brass much easier.
First bend formed and tube positioned to form the second
(Already bent running board in foreground)
Second bend formed and ready for the third
Fourth and final bend formed
After bending the strips the positions of the cut-outs were marked out and sawn and filed to shape and the strips trimmed approximately to length. Final trimming will be done after the running boards are drilled for the mounting screws and fastened in place.
The next job was to make a load of brackets to support the running boards at various points along their length. I want the running boards to be as rigid as possible to provide a good solid base for the tanks and cab. I cut the brackets from 20mm x 3mm mild steel angle using a slitting saw in the lathe. Much easier and more accurate than sawing them by hand! One side of the angle was left at full length and the other, which bolts to the frames, was reduced to ½" long and drilled for two 8BA bolts. Drilling the frames for the brackets was a fiddly job as it had to be done in situ. The positions of the brackets were marked out and the brackets glued in place with a dab of superglue. The holes were then drilled in the micro-mill. This was very awkward due to lack of space and the problem of holding the chassis! I eventually managed it by resting the chassis on blocks of wood at each end. Where possible the brackets were clamped in place as well whilst the chassis was drilled as the superglue was not very strong.
Drilling the frames for the running board brackets
The running boards were then clamped in place and marked out for 8BA csk head fixing screws, two to each bracket. The boards were then removed and drilled. They were then clamped in place again and used as a jig to drill the various brackets. Once again I had to hold the chassis somehow and used a length of narrow worktop to make a temporary drilling table on the mill.
One running board drilled and screwed in place
Makeshift drilling platform!
One problem which occured whilst fitting the running boards was that the steam manifolds on top of the cylinders were sticking up slightly too high and were fouling the underside of the boards. I should have reduced the height of these when machining the cylinders but obviously forgot! It was not practical to mill a bit off with the cylinders in situ so I eventually did the job with a sanding drum in the Dremel. There was only about a 1/32" to take off so it did the job quite quickly. The chassis was covered as much as possible to protect it from the brass dust but the whole lots going to have to be cleaned up anyway before the chassis can be run again. A good blasting with the compressor air gun should do the trick!
The thing that is becoming apparent is that at the moment the chassis is very front heavy (it's getting heavy anyway!), obviously due to the three cylinders. Hopefully when the boiler and platework are fitted it will move the centre of gravity much farther back. It will be possible to fit some ballast weights over the rear bogie if necessary.
The two front curved sections of the running boards were bent over a suitable piece of bar after annealing and trimmed to size after bending. It's much easier to make bits like this oversize and cut them to length after they have been bent. They and the buffer beams were then drilled and tapped for two 8BA securing screws. They were then removed again and a length of 1/8" square brass soft soldered on the top edge to secure the end of the intermediate section. A couple of 10BA brass screws were then fitted to hold the bar to the curved plate. The idea is to screw all the sections together and then take the running boards off and soft solder all the joints to make a good strong job. It's a bit easier to clamp and solder the bits in place though before drilling for the screws.
Front section bent and fitted to buffer beam
The final intermediate section was then cut out and the thin end bent up around a piece of 1/4" bar. This end is only 1/2" wide so was very easy to bend to such a small radius. Once again the section was initially made oversize and trimmed to fit after bending. Two more lengths of 1/8" square brass were fitted to the section to take more 12BA brass screws to secure it to the long upper section
Intermediate section ready for fitting
The section was then clamped in place and holes drilled and tapped for the securing screws, four to fasten it to the upper section and two to fasten it to the front section.
Section fitted in place
Both sides fitted
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