Xmas and the New Year saw little work done due to my full time job committments but now that's out the way for another year it was back to business. One side of the frames was marked out and the two pieces rivetted together using a few suitable holes that I knew the position of. As mentioned before I had not finalised where all the holes for mounting cylinders etc would be yet. The steel was quite tough but after a lot of sawing, filing, and blisters I finally had a pair of frames. The horn slots were filed to nearly full size and then finished to final size using an endmill in the lathe. I could have finished them by hand but I didn't trust my filing that much! When I get around to the 5" Black Five I think I will splash out on some laser or water jet frames. I don't fancy cutting those out by hand!
Finishing horn slots with an endmill
Frames after finishing the profiling
As you can see from the photo of the frames, the rear section is quite thin and will need some strengthening to stop flexing when pulling a load ( me, hopefully!) I think a long horizontal stretcher from the rear buffer beam to the rear set of horns should do the trick.
Buffer beams were cut from 20mm x 3mm angle with the depth trimmed to 3/4". The slots for the frames were cut with a slitting saw in the lathe to get them nice and square. I don't like the method of fixing the buffer beams with fiddly bits of angle so fastened the beams to blocks of 1/2" square steel machined to fit between the frames. The ends of the blocks were then drilled and tapped to take the frame fixing screws.
Cutting slots for frames in buffer beams
Method of fixing buffer beams to frames
Comparison with Flying Scotsman
Next job was the horns. These needed to be larger than normal 2 1/2" gauge size due to the bigger axleboxes required to accommodate the needle roller bearings so I decided to use castings designed for Juliet, the well known 3 1/2" gauge 0-4-0. The castings were bolted to the vertical slide using a clamp made from a bit of steel and the lugs milled to a push fit in the frame slots. At the same time the outside edges were trued up. The lugs were then trimmed to a few thou thicker than the frame material. They will be filed flush after the horns are rivetted to the frames. At this point the bottom ends of the horn castings were left unmachined. They will also be finished to size after the horns are rivetted in. The inside edges of the horns will be milled out to take the axleboxes with the frames clamped together after the horns are rivetted in. This will ensure that the pairs of horns will be exactly the same size and also exactly in line.
Milling the horns to fit the frame slots
Trimming the lugs to length
One horn was then marked out and drilled for the 3/32" fixing rivets and used as a jig to drill the holes around one frame slot. This frame slot was then used as a jig to drill the other 7 horns. Each horn was in turn used as a jig to drill its own frame slot. This saved a lot of individual marking out. The outside of the holes in the frames were countersunk with a centre drill and the horns rivetted in place with soft iron rivets. The rivets and the protruding edges of the horns were then all filed flush to the frames.
The protruding bottom edges of the horns were cut off with a slitting saw and finally trimmed flush with the bottom of the frames using an endmill.
Frames after rivetting in horns and filing flush
I thought that the process of rivetting in the horns would probably distort the frames and this proved to be true. One was still virtually straight but the other was like a banana! A bit of careful bending in the vice soon sorted this out though but I can forsee problems keeping the frames straight and true when they are finally assembled. Next job is milling the horns to take the axleboxes but I'm waiting for a new endmill to arrive before I tackle this.
While I was awaiting delivery of the endmill I decided to have a bit of light relief and make up the bodies for the two axle driven pumps which are 5/16" bore by 3/8" stroke. I could have got hold of some suitable castings but it's just as easy to build the bodies up from separate pieces. It certainly makes the machining much easier and it also works out cheaper! I've based the design on the pump for Black Five.
The pump barrels are turned from phosphor bronze rod and and the bores reamed to give a fine finish for the stainless rams which will be fitted with O rings. This avoids having to have a separate packed gland which would increase the overall length of the barrel (There is not a lot of room for the pumps to fit in). The barrels are silver soldered into a brass valve box along with a union for the incoming water feed. A separate square flange is soldered to the barrel for fixing the pumps to the stretcher.
Pump body after soldering the individual parts together
The bottom blanking plugs and the top fittings were turned from hexagonal brass bar. The pumps are fitted with 3/16" stainless balls seated in the usual way by a sharp tap with a hammer!
Finished pump bodies and stretcher
The pump rams are made from 5/16" stainless steel bar which fortunately was a good running fit in the pump bores. Each ram is fitted with a single O ring. The groove for this was cut with a 3/32" parting tool which gives the right width for a 0.070" section O ring. This enables the O ring to roll in the groove rather than stay rigid like solid packing would. Presumably this reduces wear of the O ring. The ends of the rams were slotted with a slitting saw to take the 1/8" thick eccentric rods. The original Helen rods are only 1/16" thick but I can see that wear on the pin and rod eye would be fairly rapid with such a thin rod.
Finished pumps with rams fitted
I decided to test the pumps at this stage to see if they would work. With the outlets partially blocked by a finger both pumps shot water several feet in the air so hopefully they will do the business when needed on the finished loco.
By this time the new 5/8" endmill had arrived so the next job was machining the inside of the horns to take the axleboxes. At first I tried clamping the frames to an angle plate mounted on the vertical slide with the horn overhanging the end of the angle plate. This proved to be not rigid enough due to the frame on the other side of the horn being unsupported. Eventually I clamped the frames to the angle plate with G clamps and some V blocks either side of the horn being machined. The blocks were necessary to give clearance for the endmill to pass through the horns. This proved to be a lot more rigid. The new endmill was a long series one and I struggled to get a decent cut using this, probably due to the length of the endmill. I eventually used a 3/8" endmill which gave better results.
Machining the inside of the horns
Even with taking light cuts and making several passes at the final setting the finish left by the endmill wasn't perfect but a rub over with a fine flat file soon removed any ridges etc.
I now had to decide on how to fit in some stretchers to keep the frames the right distance apart and hold them true and square. The front part of the frames should be very rigid as the smokebox saddle, inside cylinder, the front bogie stretcher, and the inside motion plate will keep everything in order here. The frames between the two leading axles are stiffened by the pump stretcher but there is not much room to fit anything between the second leading axle and the rear trailing axle due to the enormous firebox! I eventually decided on two simple bar stretchers near the bottom edge of the frames. These will be underneath the firebox between the grate and the ashpan. I made a vertical stretcher from 1/4" steel plate to fit after the trailing axle. I then made a long horizontal stretcher from 3/32" steel plate to go from this vertical stretcher to the rear buffer beam. This will act as a sort of drag box to transfer the pull of the loco to the rear coupling. Looking at photos of the original Helen chassis, I cannot help thinking that it looks very flimsy and liable to bending under load.
The two bogie stretchers and the flat rear stretcher are attached to the frames using 5/16" x 1/16" brass angle. I was quite dismayed to find that the 'angle' between the sides of the brass angle was more like 80 degrees than 90! It is obviously extruded rather than milled and not done very accurately. All the lengths in stock seemed to suffer from the same problem. I trued up the 4 small lengths for the bogie stretchers by tapping with a hammer over the square edge of a vice but I finished up milling the two long lengths for the rear stretcher in the lathe to get them square.
Milling the angle square
Bogie, rear, and bar stretchers
Before going any further with the frames I thought it would now be a good idea to try and finalise the positions of as many holes as possible in the frames. It is going to be a tedious job if I have to keep dismantling the frames to drill holes all the time. Consequently a lot of midnight oil was burnt in front of the computer doing more design work. The layout of the cylinders and valve gear has been more or less decided so the positions of the cylinder mounting holes, weighshaft bearings, inside motion bracket etc. could be marked out and drilled.
I spent a lot of time on the steam and exhaust pipe layout trying different ideas. Unless you have 2.5" gauge size fingers there is not a lot of room to get inside the smokebox for connecting pipes up and a three cylinder design, especially with piston valves, makes matter worse. I really like the design for Flying Scotsman where a steam manifold is situated underneath the smokebox and just one connection goes through the bottom of the smokebox to the superheaters. Also only one oil feed is necessary to feed all three cylinders as in the Scotsman. Splitting the feed from just one pump to give seperate oil feeds to each cylinder steam pipe can result in the oil distribution being unequal. After much thought I reckon that I can achieve the required result by taking the steam pipes to the two outside cylinders through the top of the frames between the top of the cylinders and the running boards. The outside steam pipes will then just be dummies. Whether this will work out in practice remains to be seen! I've a long way to go yet before connecting up steam pipes!
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