CF MRC

Not yet, but the whistle will probably be made of gold.

Tim

Maybe Hornby will produce one in 2mm scale, just as I finish mine!

Tim

Well observed John, but the combination lever doesn't take much stress: this may be a function of the Baker valve gear that was fitted to this engine: it seems to be bigger with UK engines and Walshaerts valve gear. What was not visible in this picture was the size of the connecting and coupling rods which were truly huge, with massive bearing surfaces about 10" across. It was a Chicago Burlington & Quincy 4-8-4.

Tim

We will be working on the KX goods yard and York Way. Lambourn will also be present.

Tim

Is this also modelling? (1/3rd scale). First photo, at speed, on the South Bank in London.

Tim

Not really on my workbench, because that is 4,665 miles away, but I visited the Colorado Railroad Museum today. The first photo shows how our American colleagues do valve gear and the second shows a group of early-stage P2s, en-masse, at the Buffalo Bill museum.

Tim

Those are gorgeous wagons Jim, especially the second one. We have to be bit wary of etched wagons, because they come in a bit heavy in a long train, especially with the hilly nature of our layout.

Tim

I can see your point Chris, but it would probably take me longer to draw it than make it - and I like the challenge. No pain, no gain as they say.

Tim

The block of steel did indeed release the spirit of a union link. It was filed roughly to shape at one end and slotted with a piercing saw.

After a bit more shaping the embryonic union link budded off the lump of steel and the other end was then slotted. The link could be held for filing by using pivot steel (or similar) through the holes and then mounted in the vice. As an aside, none of this work would be possible without a top quality Swiss watchmaker's vice and Swiss Vallorbe needle files.

The link can be seen near to completion in the fourth photo. Unfortunately there was then a union dispute, but this was settled with silver (solder). Not quite as good as I would like, but it moves freely, stays more or less horizontal throughout it's movement and is good enough for government work.

The copper wire visible in the assembled photos through the crosshead link is temporary: it will be replaced with a steel pin when appropriate.

Tim

Too easy Jerry. You have a picture of me holding the bit that the semi circle came from, the N gauge driving wheel of the Johnson 7' 9" single - nearly forty years ago!

Tim

"Within every block of wood and stone, there dwells a spirit, waiting to be released.”

— Hap Hagood

So this piece of steel is waiting for the spirit of two union links to be released.. Four holes have been drilled already.

Tonight's competition is to identify what this bit of steel came from in my junk box.

Tim

If you are making fully working Walschaerts valve gear then the valve spindle needs to function as a moving pivot for the radius rod, running in the valve spindle guide. The distance between the two sides of the guide is 0.6 mm on the engine so I needed a very narrow pivot for this component. The most space-economic way of achieving this was to wrap a length of steel strip 0.3 x 0.4 mm in section through the pivot hole and then close it round and soft solder where the two arms meet. The first photo shows the fire-stained combination lever with the steel strip on it's first bend. This was then annealed by heating again in the flame and the bend completed. The area to be soft soldered was cleaned up with a file to allow good penetration of flux and the soft solder. Second photo shows the finished article: the solder could not stick to the stainless steel combination lever, so keeping the pivot free.

The lever can be seen in-situ in the side view. The union link (yet to be made) should be horizontal when the piston is in mid-stroke. In the top view the pivot and valve spindle is just visible in the valve guide and the joggle in the combination lever is also very obvious in this view. The union link will be filed up out of a small lump of steel In order to make the forked joints.

Tim

P.S. For Richard's piece of mind, no fingers were damaged in the making of these components.

Just as well you're not a surgeon, (or maybe you should have gone to Specsavers) as I'm not sure how that can be the right index finger. It's all part of the toughening up procedures for soldering.

Tim

Making Lord President's combination levers has been a bit frustrating, with the first one going into deep space. This bit of valve gear needs to have holes for the valve spindle and radius rod at the top and union link at the bottom. I decided to make it out of stainless so that the forked joints won't solder up too readily. It can be toned down by heating in a flame. One way to make small components is to make them with a handle which is then cut off, when no longer needed. The second photo shows the combination link being tried in on the LH cylinder using the handle to steady it. The link will have a joggle in it so will come up shorter, when completed.

Tim

A certain Mr. Wright can be seen using epoxy to secure such items in one of his Right Track Loco Construction DVD's, so I wouldn't be overly concerned......

 

Tim

As promised, I modified the slightly obese connecting rod. Happier now. The next one will be better.

Tim

About 0.5 mm at the thick end. I always start off thick and thin down where required. It gives a good appearance of mass in the bearings.

Tim

The connecting rods for Lord President are, of course, tapered and fluted. I had thought about milling them out, but the taper makes life tricky. In the end I simply made a skinny rod and then silver soldered two sides to it to make the webbed casting. These additions were then filed back until they almost disappeared.

The little end pin was initially a drill shank silver soldered in place. I subsequently learnt that this would not accept soft solder for the securing collar, so it was replaced with a bit of watchmakers pivot steel. Clearances are tight, but seem to be working out OK. Looking at the unkind photo, I will take the top web off, thin the rod down and soft solder a new web in place.

Tim

Sorry for the dental stuff, I do use a lot of watchmaking stuff as well.

The technique for casting with a potato is that the alloy is heated in the cone of the investment ring until molten. A wet half potato is then firmly placed on top. The flash steam from the potato drives the metal into the mould space. Other techniques that used to be used are a stirrup and chain (a better engineered version of Jim's string), swinging the casting ring in the stirrup around by hand, once the metal is molten.

Tim

At Guy's, as students, we had centrifugal casting machines that were wound up: effectively clockwork powered. They required a choreographed action of placing the hot casting ring in the arm, heating the gold in the crucible with a gas torch and letting go the centrifugal arm at the correct moment. We did our phantom head course with real gold and it was quite easy to harvest splattered gold from around the casting machine, if you followed the less savvy students who put the ring in back to front. In this way I collected enough material for my first gold safety valve. Students nowadays don't have half as much fun!

Tim

Two crossheads & pistons

These little devils were quite fiddly. I made the first one on the left hand side by dead reckoning and serendipity. The second one was, of course, much easier as I knew what was needed; so I photographed it's construction

The slipper and socket for the piston rear end was cut out of sheet steel with a bit of excess material for filing back later. This was then bent up with the piston socket going backwards and the slipper folding forwards. The metal was scored with a slitting file to ensure that it bent predictably. The piston was made from a broken twist drill (I have plenty from this project!) and the socket was augmented by a small length of syringe needle towards the front.

The whole lot was then silver soldered up. Following the article on silver soldering in the latest MRJ I got some 'Silver Solder Paste Easy 15gm Syringe' from Palmers metals. This is really much easier than separate flux and solder for these very small jobs. The long tag hanging down was subsequently scored to allow it to bend right back on itself to form the basis of the arm which will be surrounded by the forked union link. This was then silver soldered again, to make the whole assembly very strong. Finally, the two holes for the little end and the union link were drilled.

At the moment, the crossheads can slip back towards the wheels, but the connecting rod will hold them out, as will the union link and combination lever. The connecting rod will have the little end pin silver soldered to it, pass through the crosshead, and then the big round boss and castle nut will be represented by a piece of syringe needle and the pin slightly poking through. Not quite prototypical, but I don't think I'll loose any sleep over it.

Tim

(P.S. Do you like my new avatar? LNER publicity sticker from the era)

You could always use a half potato for driving the molten alloy into the investment cavity, Jim. Bits of string could be risky!

Tim

A cast backhead.

As intimated in previous posts, I intended to make a cast backhead for 2003. So the pattern was made from styrene - a little thickened in some areas to allow for metal flow. The details were broadly derived from an A4 backhead.

This pattern was sprued with wax into the bottom corner and mounted onto a casting cone. The spherical swelling on the sprue acts as a metal reservoir close to the pattern. The casting ring is lined with a thick card-like material to allow swelling of the investment (not sure why these images are horizontal). The vacuum-mixed gypsum investment was poured onto the pattern in the casting ring, making sure that there were no air bubbles. Once set, the investment is taken up to a high temperature (700 dec C) that burns out the plastic and wax, leaving a space for the incoming molten metal. At the same time, the investment expands to compensate for the shrinkage of the molten metal as it freezes.

The casting was made using an induction-heated vacuum casting machine with 1030 deg C melting point alloy: "Phantom Metall NF". Once cool, the student's alloy casting (brass) was divested and then bead blasted to remove the remnants of investment. The casting was then fettled and bolted into the cab. It needs the fire screens fitting to protect the driver and fireman's legs. At least they won't have to worry about a dangerous drive shaft on this engine!

Tim

(P.S. I expect this has stimulated a few of Jim's memories from his dental undergraduate education)

Don't forget that there are lathes at the MRC that you could use, if required, Justin. Or alternatively, in another Roman City messed up by Boudicca.

Tim

I have fitted the motion support brackets for 2003. These are soldered onto two brass bars that are, in turn, bolted through the PCB frame spacer. I also soldered on a small web around the edge of the casting: this is quite conspicuous on the real thing and makes the whole assembly look businesslike. Don't know why, but the cylinder looks a little whimsical / sad in the first photo. Second photo shows the bracket sitting under the running plate. The width has come out about right as can be seen with the body in place. This will need some insulating tape or fag paper and Araldite on it to maintain insulation.

Need to finish off the pattern for the backhead (it was started at the MEE at Ally Pally) & then the crossheads and pistons.

Tim