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25/07/06

The inside motion plate is a simple fabrication from steel plate with brass angle rivetted on the sides for attachment to the frames. Two small 'lugs' are rivetted top and bottom of the slidebar slot for attachment of the slidebars. The motion plate also carries the bearing for the long lever of the conjugated valve gear and the mounting bracket for this is a shaped block bolted to the plate.

Inside motion plate

The motion work was then temporarily assembled and everything lined up properly and moved smoothly with no tight spots. The only problem that came to light was that the connecting rod fouled the end of the bottom slidebar. At the moment there is no weight on the axles and the axle boxes are at the lowest point in the horns. When the loco has a few more bits added the boxes will rise in the horns and the clearances will be ok. However, just to be on the safe side I filed a bit more off the chamfer on the end of both slidebars to increase the clearance.

Motion plate fitted with cylinder etc.

Whilst making the motion plate my thoughts turned to the problem of lubrication for the inside motion etc. The inside crosshead and slidebars will be hidden under the smokebox saddle and so will be inaccessable from the top for pre-run oiling. I am not very keen on the idea of turning the loco upside down before every run to oil all the inside bits so I came up with the idea of fitting a small oil tank where it can be got at easily for filling and running small pipes to deliver oil to all the inaccessable motion. I may even fit the tank with a mechanical lubricator to actually pump the oil to the motion work. I had been wondering where the mechanical lubricator for the cylinders would go as there is no room behind the front buffer beam which is the usual place to fit one (The space behind the beam is filled by the inside cylinder!). However, there is a fairly big gap behind the inside motion plate and I should be able to fit the cylinder lubricator there along with the oil tank for the motion. The drive for the lubricator can be taken from the axle pump eccentrics or some other convenient point.

With the remote tank idea in mind, the top slidebar was drilled with a small hole to take the oil feed. The crosshead was drilled with a countersunk hole on the top bearing surface to collect oil and feed it to the small end. Another small hole was drilled in the bottom of the crosshead to feed oil to the bottom slidebar.

28/07/06

The long and short beams for the conjugated drive for the inside valve are fairly simple milling and filing jobs from mild steel bar. To ensure accurate positioning of the pivot points the blanks were set up on the vertical slide and the holes drilled using the crosslide micrometer dial to set the distances apart. Obviously, any large errors in the 2 to 1 gear will affect the timing of the inside valve but I don't suppose a few thou will make any significant difference.

The main pivot for the long beam is a plain length of 1/4" silver steel drilled and tapped at the top to take a retaining bolt and the smaller pivot pin for the short beam is a similar piece of 1/8" silver steel, again drilled and tapped for a retainer. The large bush in the main bearing bracket and the smaller bush in the short beam are turned from the Peek material again. My reason for using this material here was that the bearings can be made quite a tight fit on the shafts and still move freely. This will help to eliminate any backlash in the finished motion.

Beams for 2 to 1 gear

Incidently, when I was first drawing out the valve gear I had the main bearing for the long beam mounted underneath the beam. I then realised that it would be in the way of the inside connecting rod so I had to move the bracket so that is above the beam.

The small beam is held onto it's pivot by a countersunk washer and 8BA countersunk screw and the main beam by a 5BA hex bolt and washer. The 5BA bolt is drilled through the centre and the head countersunk to act as a oil cup. A small hole is drilled through the wall of the 1/4" shaft to feed the oil to the bearing.

Beams mounted in frames

01/08/06

I thought it was about time I finished the axlepump assemblies so the next job was to complete the eccentric straps (I actually bored the straps and rough finished them when I had made the eccentrics earlier). I had found a couple of suitable castings amongst a mixed lot I had bought some time ago and machined these up. The castings were sawn in two, the mating faces cleaned up and the straps drilled and reamed and 7BA bolts made and fitted. After bolting the two halves of the straps together they were held in the 4 jaw and faced off both sides to a thickness of 3/16". They were then bored out to a nice running fit on the eccentrics. The oil boxes etc. were then milled to final size.The lugs on the straps were slotted to take the ecentric rods which are made from 1/8" mild steel. The embryo rods were soldered into the straps and then two holes drilled and tapped through the lot to take two 8BA bolts to secure the rods firmly. The ends of the rods were then filed to shape using filing buttons and the sides shaped by milling. Finally the rods were fitted with Peek bushes to take the 1/8" dia. drive pin for the ram. Incidently, the rods are very short because the pumps have to be very close to the axles due to the lack of space. However the pump throw is only 3/8" so the angularity of the rods when at the top and bottom positions is not too severe.

Axle pump straps ready for fitting

The drive pins for the rams are simple lengths of 1/8" dia. silver steel press fitted into the rams.

Straps assembled and fitted

03/08/06

Some time ago I had turned up the 4 buffer stocks from 5/8" square mild steel. They are a quite basic design with parallel stocks reamed out to 1/4" diameter for the heads and fastened to the buffer beams with 10BA nuts and bolts. As a bit of light relief I decided to finish the buffer assemblies by making the heads.

The heads are turned from 11/16" freecutting mild steel bar and four blanks were turned down to 1/4" diameter for the shanks and then parted off at the full diameter for finishing the front faces.

Parting off a buffer head blank

For the A1 I had machined the radius on the front of the buffer head by machining steps across the face and then smoothing with a file but it is difficult to get all the heads identical using this method. In issue no. 4277 of Model Engineer Tim Coles describes a simple but brilliant way of machining the heads which guarantees that they will all be the same. A length of rod is put between the headstock and the cross-slide at an angle and as the cross-slide is advanced across the blank, the bar pushes the cross-slide away from the headstock and the cutting tool traces out an arc equal in radius to the length of the bar.

In this case I used a piece of silver steel approx. 2-1/4" long which was rounded on one end and ground to a point on the other. The rounded end sits in a depression which happened to be in the end of the shaft for the lathe back gear mechanism and the pointed end engages in a small centrepunch mark in the front of the cross-slide. The centrepunch mark was positioned so that when the lathe tool was in the centre of the buffer head blank the silver steel was parallel to the lathe axis.

 

The blank was held in a collet and cuts taken across the face, at the same time putting light pressure on the lathe saddle to keep the cross-slide pressed against the end of the rod. The pressure is really only necessary when winding the cross-slide back to the beginning of the cut otherwise the bar falls out! When the front face of the head was reduced to the right thickness at the edge, the edge was rounded off with a fine file and the face finished off with fine carborundum paper.

The heads are retained in the stocks by 7BA bolts put through from the back of the stocks and threaded into tapped holes in the shanks. The buffers are fitted with short springs made by cutting some longer ones in half. They are probably a bit too strong but I don't suppose the buffers will be doing much anyway!

Completed buffers bolted onto the beams

05/08/2006

I fancied a break from machining work so decided to do a bit of tin bashing and make a start on the boiler. Helen's boiler is a pretty simple affair apart from the very long firebox which is needed to give the heating surface necessary to steam the three cylinders. It will be interesting to see how easy it will be to fire it. I think the firehole will need to be a decent size to give a good view of the fire at the tubeplate end!

The barrel is a length of 3-1/4" diameter by 16swg tube with a seperate wrapper for the firebox end. I think this is easier than using a full length tube which then has to be split and extended either side for the firebox wrapper. Most writers recommend truing up the ends of the barrel in the lathe but this means turning up a couple of wooden discs to put in the ends of the tube, one to enable the tube to be gripped by the chuck, and the other to support the outer end of the tube using a tailstock centre. It's a lot easier to just file the ends square using a piece of thick paper wrapped around the tube to give a straight edge to work to. If the edges of the paper are lined up where they overlap the edge will be perfectly level and square all around the tube.

Using paper to true up the ends of the tube

Some thought had been given to the type of joint to use where the throatplate meets the barrel. LBSC and Martin Evans invariably used a simple butt joint with the throatplate resting on the end of the barrel and a good fillet of silver solder built up at the joint. The alternative is to flange the top curved edge of the throatplate where it meets the underside of the barrel as well as the sides. It can be a bit tricky making this type of double flanged throatplate so I adopted a joint somewhere between the two. The top of the throatplate still butts against the inside edge of the barrel but the barrel is sawn to produce little tabs which are bent down against the front of the throatplate. This will give the benefit of the greater strength of a fully flanged joint but should be a bit easier to do.

Tabs cut and bent down for the throatplate joint

The backplate was made next from 13 swg copper and flanged over a simple former made from 1/8" steel screwed to 1/2" plywood to give the extra thickness. You do get slightly better results using all steel formers but they are a lot harder to cut out! The main problem with the wood backing is that the copper tends to get bent around the steel plate and grips the wood very firmly, making it difficult to remove the boiler plate after forming . All steel formers don't give this problem. The same former was used for the throatplate which is also 13swg.

Backhead with former

Next job was to bend up the firebox outer wrapper from 16swg sheet. A piece was cut the right width to suit the length of the wrapper and left slightly over long to allow for trimming after bending and soldering. I happened to have a piece of thick wall copper tube the same size as the barrel so this was used as a former for the top of the wrapper. A centreline was scribed down the wrapper sheet and another one down the former tube. The sheet was then clamped to the tube with a length of bar and G clamps ensuring the centrelines aligned. This ensured that the wrapper would stay square to the axis when it was bent around the tube.

Forming the outer wrapper

The two reverse curves at the side of the wrapper were made by using a smaller diameter bar. It is a bit tricky to get these bends in the right place but I managed it eventually using the backplate as a template. Final shaping was done by clamping the wrapper around the backhead.

Using backhead as a former for final shaping

The barrel, wrapper, and throatplate were then assembled using 10BA nuts and bolts put through a few holes drilled in strategic places. The alignment of all the parts was then carefully checked with a straight edge and when I was happy that all was ok, the nuts and bolts were replaced with 1/16" copper rivets ready for soldering. It pays to use as few rivets as possible as they are a potential source of leaks. Any gaps in the barrel/throatplate joints were plugged with slivers of copper tapped into place. It is important not to have any gaps as even the Silverflo 24 is not that good at filling gaps and Easyflo will run through gaps like water!

Using nuts and bolts for initial assembly

 

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