I thought it might be a good idea to include the dates when the updates are done so I'll do this in future.
The meeting at Rugby turned out to be a good day with the weather being kinder than expected although there were not so many locos running as last year. Helen seemed to get a good reception from other members so it's full steam ahead!
I thought I had better tackle the coupling rods next and get those out of the way. The rods need to be in three sections, the centre section having a knuckle joint at each end. They are machined from 5/8" x 3/16" mild steel and to save work will be left plain rather than fluted ( plenty of full size engines have plain rods! )
The centre sections were tackled first. First job was to drill the crankpin holes and to get the centres correct an adjustable drilling jig was used ( as for Flying Scotsman ). The blanks were drilled and reamed 1/4" dia. and tried in place on the wheels. There was a slight tightness when the wheels were turned but the holes were a very close fit on the crankpins anyway. Any slight errors in the hole spacing can be corrected later when the bushes are fitted.
Once again I avoided having to mark out the outline of the rods by sticking a paper template onto the blanks and then cutting round the outline with a knife, marking the steel at the same time. Both blanks were rivetted together so that they could be machined as a pair. Short lengths of 1/4" bar in the crankpin holes ensured accurate alignment of the two blanks. A few holes were drilled around the outline and the blanks roughly sawn out to shape.
Rod blanks rivetted together and the paper template
The blanks were then milled to the final outline with the rounded ends etc. finished by hand filing. To make this easier some filing buttons the same diameter as the various curves were made from silver steel bar and hardened right out. These were also used when milling the straight edges of the rods to act as 'stops' to prevent milling too far!
Filing buttons made from hardened silver steel bar
.....................................Milling the edges of the rods using the buttons as guides..................Rods after milling and filing the outlines
LBSC recommended using a pin drill ( basically a D bit with a pilot pin ) for maching the tongue of the knuckle joint but I used an endmill instead, using a drill held in the chuck to line the pivot pin hole up with the lathe spindle centreline.
Milling the knuckle joint
Last job on the rods was to reduce the thickness on both sides and again the filing buttons were used to act as stops for the milling operation.
Milling the sides of the rods
The leading and trailing rods were machined in the same way as the centre ones, the slots for the tongue of the knuckle joint being cut with a slitting saw. The joints were temporarily pinned with bits of 3/32" rod and the crankpin holes drilled using the jig again and reamed 1/4" dia. The complete rods were then tried in position and any misalignment of the holes corrected by carefully easing the crankpin holes in the right direction with a file. Fortunately the holes were nearly spot on so not much correction was necessary. One fault I did find was that one of the leading crankpins was not perpendicular to the crank boss causing the rod to bind in one position. I am not sure how this happened as the crankpin holes were drilled and reamed in the micro-mill to make sure they were perpendicular to the bosses. Anyway the pin was carefully removed after heating it with the blowtorch to break the Loctite bond and the hole in the wheel boss eased over so that the pin could sit correctly. The pin was then re-loctited in place. I now had a pair of coupling rods with all the crankpin holes in the right place but obviously the rods will need to be drilled and reamed to take bushes so the alignment will have to be checked again after the bushes are fitted.
The next job was to fit the proper pins to the knuckle joints and I eventually decided to use plain pins made from 3/16" dia. silver steel press fitted into the outer legs of the joints and a running fit in the inner tongue. This should give a long life as there is very little movement in the joints anyway.
The rods were clamped to the vertical slide and the original 3/32" pin holes drilled and reamed slightly under 3/16" dia. When I had bought the O gauge wheels for the Royal Scot and the A1 from Alan Harris I also bought a special size reamer which gives the correct press fit for 3/16" dia. axles. This is the reamer used. The joint was then taken apart and the inner tongue re-reamed to 3/16" dia for a running fit on the 3/16" pin. 4 pins were then faced and parted off from 3/16" silver steel and pressed into place.The pins were made slightly over length so that they could be filed flush with the outer face of the rods. They were left protruding slightly on the rear of the joints as I may put a touch of soft solder on the back just to make sure they cannot work loose in service.
.................................Reaming knuckle joints............................................................Finished joint
The rods were then cleaned up using carborundum paper and drum sanders in the mini-drill to remove any machining marks and countersunk oil holes drilled in each boss with a centredrill.
The final job on the rods was to enlarge the crankpin holes and fit the bushes. The holes were opened out by clamping the rods on the table of the mini-mill and using a piece of 1/4" rod in the chuck to accurately line the holes up with the spindle. They were then drilled and reamed to 5/16" dia.
I had got hold of some pieces of the TecaPeek PVX rod mentioned previously ( Page 6 ) and decided to give this a try for the bushes as this would give me an idea as to how easy it was to machine etc. One piece was 10mm dia. which was ideal so a set of bushes was machined from this. As expected, it is a delight to machine and parts off a dream! It is more expensive than bronze but it's much easier to work with. It is quite soft so it will be interesting to see how it performs in service.
The bushes were finish reamed after being pressed into the rods and I did have a bit of a problem here as my reamer is not perfectly sharp and did not cut the plastic very well. I eventually used a sharp 1/4" endmill to take the final skim off the bore.
..........................The TecaPeek PVX rod.................................................................. A finished bush
After all the bushes were fitted, the rods were tried in place again. On one of the rods the trailing bush was slightly out and needed easing with a fine file. The plastic's very soft so you have to be careful not to be too enthusiastic with the file! When I was happy with all the bushes, it was time to destroy all the careful fitting by opening out all the bushes except those on the driving crankpin to give plenty of running clearance! This was done using an adjustable reamer set slightly above 1/4" dia. I had bought a set of these adjustable reamers some time ago but frankly the quality is very poor and they were a waste of money. I found the best way to use the reamer on the PVX bushes was to revolve it backwards otherwise it tended to dig in. That way it did the job quite well.
Finished coupling rods
I must admit that I'm glad the couplings rods are now done as the job seemed to take ages. There's quite a lot of fiddly work in them really. I think it's time to start thinking about the middle cylinder so that will be the next job. I'm still waiting for the bogie wheel castings as they are out of stock at the moment.
I didn't manage to do much over the past week or so due to running our local Legion club whilst the stewardess was on holiday but that's out the way now so back to work!
As mentioned previously the cylinders will be fabricated rather than use castings. I had obtained some cored gunmetal bar for the cylinders and some solid gunmetal bar for the valve chests so a start was made on the middle cylinder. The cored bar was held in the 3 jaw chuck with the other end supported by a live centre. Fortunately the hole in the bar was smaller than the outside diameter of the centre and also central in the bar. I had intended to use a 3 point steady to support the bar but the outside surface of the bar was too rough for this. A suitable length of the bar was turned down to 1-1/4" dia (the finished diameter of the cylinder) and then sawn off. The 'tube' was then centred in the 4 jaw, bored out to 13/16" diameter and then both ends faced off to length. The finished bore will be 7/8" diameter but this, along with the valve chest bore, will be finished to size after the bits of the cylinder are finally silver soldered together.
.................Turning the outside of the cored bar to size...........................................Boring the tube
Next job was to machine a circular recess along the embryo cylinder to take the 3/4" diameter valve chest and this was done by bolting the 'cylinder' to a small faceplate and offsetting it by the correct amount from the lathe axis. The recess was then turned with a boring tool. The valve chest was then turned from gunmetal bar and cut off to length.
............................Maching the valve chest recess.......................................Valve chest sitting in the recess
The valve chest was bored out to 3/8" diameter (finished diameter will be 7/16") and faced to length. There will be no seperate liner for the piston valve and the ports are cut directly into the inside wall of the valve chest. I made a special tool for this operation by grinding down a spare boring tool to give a square cutting edge exactly 3/32" wide, the width of the ports. The tool was carefully aligned with the end of the valve chest and then, using the micrometer dial on the leadscrew, fed along the bore of the valve chest the correct distance for the first port. The port was then cut by feeding the tool into the side of the bore. The remaining ports were then cut using the micrometer dial to advance the tool down the bore by the correct distance. There is a total of 4 ports to cut because, as mentioned before, I am using the Henry Greenly double ported design for the valves.
The port cutting tool
The valve chest was held in a vice on the vertical slide and the steam passages machined to connect the two ports at each end of the valve to the steam passages in the cylinder. The passages are contained within the joint area between the valve chest and cylinder so that no connecting pipes are necessary which would make the job more complicated. The only external connections are for the exhaust passages from the ends of the valve chest to the blast pipe. A similar setup was used to machine the corresponding passages in the cylinder.
Machining the steam passages in the steam chest and cylinder
I also decided to machine a groove at each end of the cylinder bore so that the incoming steam is distributed around the whole of the cylinder rather than just at the top. Another advantage of this is that the cylinder cover spigots can be made slightly larger than the cylinder bore thus allowing the cylinders to be rebored at a future date without affecting the fit of the cylinder covers.
Cylinder and valve chest ready for soldering together
The plan was to silver solder the cylinder and valve chest together first using a high melting point solder and then add the remaining bits using easyflo No. 2 rather than try and solder the whole lot at once. The joint area between the cylinder and valve chest was cleaned, fluxed, and the two components clamped together checking that they were aligned correctly. The joint was then soldered using silverflo 24. This turned out to be a bit of a struggle and a lot of heat was needed to accomplish this successfully. The gunmetal valve chest actually started to flake on the surface but fortunately no serious damage was done. I think for the outside cylinders I'll stick to easyflo for the lot as it's much easier to use.
The mounting plates for the cylinder were machined from 1/4" x 1-1/2" brass bar and made as a pair by the usual trick of soft soldering the two pieces together and machining as one. They were made oversize so that they could be machined to final size after assembly.
.............Machining mounting plates to fit cylinder/valve chest...............................Trial assembly
The last items needed for the cylinder assembly are the steam and exhaust connections. I tackled the exhaust first and after some thought decided to make a manifold from brass bar soldered alongside the valve chest with the exhaust pipe leaving at the rear end. This will make it easier to connect to the blastpipe than the usual arrangement where the exhaust pipe connects in the middle of the cylinder. The exhaust ports were machined using the vertical slide and are simple rectangular slots in the side of the valve chest. The connecting manifold was milled from 1/2" x 3/8" brass and is basically a channel with closed ends. I would have preferred to have used 1/2" square brass which would have given more room for the exhaust pipe connection on the end but I didn't have any to hand.
............................................................Milling the exhaust ports...............................................Milling the exhaust manifold