An LNER A3 for the National Railway Museum. PDF version
As part of its golden anniversary celebrations in 2006, the Gauge 0 Guild is providing a 7mm scale model of Flying Scotsman to be part of a ten year exhibition at the National Railway Museum.
The engine was presented by (the late lamented) George Hinchcliffe to the Museum on the 20 March, which proved to a tight deadline that had consequences (see later).
The name Flying Scotsman is perhaps rather more apt than I first thought since this job has gone through my workshop in a little over a month. This has in turn caused problems, rushed jobs are always prone to things going wrong and this one was no exception.
The various parts were provided at reduced or no cost; the kit from David Andrews, wheel castings from Alan Harris, motor/gearbox from ABC and plates donated by Guilplates. I built it at no cost and it was professionally painted in BR blue, circa 1949-50 by Dennis Morley for next to nothing.
So what do we get in David's box? This is large and robust and would certainly hold the completed engine where it not for the fact that Philip Dredge made a special hardwood case for it.
As you can see, there is a great deal. All the castings appear to be crisp and neat (which proved to be case on most of them) and the quality of the etches is outstanding. I particularly like the 0.7mm thick nickel silver etches for the chassis and motion.
There is also a bag containing the nuts and bolts - unusual in that many of them are a beefy 6BA - handrail knobs, ready turned crank pins and plunger pickups. Back to Top
An important element of this project is research since, not being an adherent of the "London and Nearly Everywhere" I have little, if any, information about it. Mike Marritt kindly loaned some books and the KRM found a picture at about the right time and others have been provided by members of the 7mm E-group.
These engines had a complex history with many different variations. The Scotsman started life as an A1 and all sorts of changes have occurred over the years, some of which are open to question. For instance, there are two schools of thought on the number of spokes in the trailing wheels. Some say ten, others twelve.
Flying Scotsman today actually has trailing wheels with nine spokes! (As apparently does the V2 in preservation.) The important things from the point of building the model were those that are visible. Did it have a Banjo dome? Was it right or left hand drive in 1949-50? The changes to these engines make the GWR 517 Class seem easy to research in comparison but it has been most interesting.
So, now to the building, beginning with the tender as usual:
I started, as usual, by building as much as possible "in the flat" before commencing assembly. All the material used is quite thick, especially the nickel silver, so cleaning up the cusps is essential, particularly where parts are seen edge-on.
Securing nuts are nice, beefy; 6BA and where they need to be fitted there are etched hollows that exactly match the shape of the nut; a great idea that makes the job easy, accurate and quick.
The pictures shewing the construction are fairly self explanatory. However, much care is needed to get the curves right. Attention to the cusps also ensures that the parts fit as they should. Back to Top
Getting the coal space unit in is a small challenge but patience and a steady hand win out in the end.
The parts for the chassis cleaned up with nuts fitted and bearings in. I originally lightly sprung the two centre wheels as you can see. The etches allow for this by providing half etched extensions for the bearings. A simple matter to file them to shape, checking carefully for fit as one goes along, and some steel guitar wire soldered to the bearing and the side of the frame.
However, I later scrapped them as too fussy and used the designed method of a screw above each axle to reduce vertical movement.
More pictures of the tender at various stages of construction. I added some brass angle when fitting the rear buffer plank to give more strength. The whole of a train's weight will be taken by this (Assuming a 'glass model' ever gets the opportunity that is).
The brass castings for the tank vents were missing; I did not want to wait for some to arrive so made some up from brass rod instead.
Tender Brake Gear.
If assembled as per instructions would make removal of the wheels quite difficult so they were modified to be removable. A length of small bore tube 4mm long was soldered on the upper brake rigging fixing point and the shoes simply sprung on to them. It was necessary to alter the fitting of the cross bar and leave it as part of the fixed gear. The doors were later removed when I realized that on the A3, the doors (separately provided) were on the cab sides. Back to Top
The first thing to do was set up the master chassis jig using the rods to get the spacing right for the mock axles. (It is not really bent; the close-up lens tends to distort the picture.) Next the bushes are slid onto the mock axles and the first side frame offered up and soldered to the bushes.
The same procedure follows for the other side frame but this time the frame goes in first followed by the bushes.
Finally, the two halves are soldered together using the various spacers. The result should be a dead accurate chassis. Since this is the first time I have used this tool, we shall have to wait and see when the wheels are on.
Further work on the chassis will continue after the body has been completed and delivered to Dennis Morley for painting because of the tight deadline on this job.
The footplate has some complex curves and so the built-in jig that comes with it proved to be a great boon. Care is needed to get the curves right but the jig keeps it all square. The integral jig will stay in place until the cab and firebox/boiler/smokebox are fitted. Due to time constraints it was not possible to make them removable. Back to Top
At the front of the engine there are two, thick; nickel silver parts that represent where the frames come through the footplate. There is a small error here. The slots in the footplate need to be lengthened by about 4.5mm to allow the parts to fit correctly. David has altered his instructions to reflect this.
The boiler comes in two parts, a parallel section and a taper section (which comes ready rolled) and each is wrapped around circular formers that fit in etched grooves. The simplest way once the boiler was rolled was to stick it together with some heat resistant tape at the ends prior to soldering up. I used Sellotape for the middle bit since there was little heat generated there.
Do take care that the straight section is rolled the correct way with the etched grooves at the ends. I didn't and rolled it the wrong way! I fitted the firebox and two parts of the boiler together using some 3mm brass rod as pegs in the etched holes.
It is important that the formers are lined up on the witness marks at the centre of the etched grooves so that these holes line up properly. The three parts are shewn here with the pegs soldered in. Each peg goes the full length of both the firebox and the parallel boiler section. Back to Top
Here the boiler/firebox is nearing completion with the cab front temporarily fitted so that it can be test fitted to the footplate unit. There are tabs at the base of the cab front that fit into slots in the footplate. A few parts still remain to be fitted but now is the time to decide how best to fit the boiler to the footplate.
The instructions assume solder but I do not like the idea of being unable to separate them at some later date. In the end the boiler/firebox was bolted to the cab front and the smokebox saddle but they will still not come apart due to the cab fittings now being in the way.
Here are parts of the cab ready for fitting and the smoke box door. The lamp iron is a lost wax item left over from a DJH kit, exactly like the one in the only good picture of have of Flying Scotsman taken close to the period modelled.
Here are three pictures of the finished body temporarily mounted on its chassis.
The body for both the engine and tender went off to Dennis Morley's paint shop whilst I concentrate on completing the running chassis.
The Engine Frames.
The chassis components having been further worked on together with several components that will later be fitted. They are the radial truck for the rear wheels, the base of the firebox, the frames for the bogie, the motion bracket, the cylinders and the front step unit.
The chassis, where it bends outward to support the cab, is both narrow and half etched on the bend. I was a little concerned about its strength in the long term (years from now) and so soldered some scrap etch, suitably bent to shape, to the inside to strengthen it. Back to Top
The motion bracket and the cylinders bolt on so that all the motion can be taken down for painting and maintenance. Well designed and, once the parts are properly cleaned up and the cusps taken off, a good fit. The radial truck is a particularly neat piece of design. The whole unit bolts in place and the wheels can move from side to side in an arc and turn about their front to rear axis. There is nothing here beyond the abilities of an average modeller with some experience of complex etched kits.
There is however, a choice of using a simple pony truck. On top of the chassis, between the front and middle driving wheels, are fitted two arms with circular holes in them. These are from part "LL" and are designed to hold parts of the sand pipe assembly.
The part is supposed to fit across the frames but, once bent to shape, is in fact too short. I simply cut off the centre portion and soldered each arm separately.
The cylinders and slide bars make up into strong, square units once the parts have been cleaned up. The slide bars need careful work since the parts are relatively delicate in spite of being lost wax cast in nickel silver.
It is critical that the piston runs smoothly and easily in the slide bars. I found that by clamping the parts with magnets on the steel RSU plate, I could use a steel set square to ensure that the slide bars were at right angles to the front face of the cylinders.
The Valve Gear.
The conjugated valve gear was next. All the parts actually move; I did it that way simply because I could. I doubt much of will be visible once the footplate is in place. Back to Top
The motion cleaned, polished and largely made up ready for fitting. Most of the linkage is by nickel silver rod soldered into the back of each joint. Except that is for the jointed coupling rod which uses a steel rivet provided in the kit. There are brass rivets provided too but I wanted to avoid brass in the motion as much as possible.
The next picture shews the chassis with wheels and coupling rods fitted being run-in. Now of course you are wondering why it has a set of Slater's driving wheels. One of the aims of these articles is hopefully for others to learn by my mistakes, especially the dumb ones.
The Harris wheels were turned up with the intention of using Gibson telescopic axles, as I have done in the past. However, when it came time to fit the axles, they proved to be of a smaller diameter than the that in the wheels (or the axle’s holes were too large!). I did not have time to make a set of axles to fit. One of the dangers of trying to work to a deadline I suppose.
Having got the chassis run-in over a couple of hours on the rolling road it runs almost silently and silkily smooth at crawling pace, it is now time to start fitting the motion and cylinders.
My intention was to rivet the motion together using nickel silver rod and most of it is so done. However, so that the motion can be tested properly and taken down with relative ease in the future, some parts must be bolted.
The connecting rod is joined to the slipper and its associated motion parts with a lost wax nickel silver cast rivet. I tapped this 10BA and fitted it with a nut behind the slipper where there is plenty of room. The associated motion parts were then fixed to this part with a 14BA nut and bolt, unfortunately, in brass. This enables the motion to be removed but still retain the connecting rods for testing.
The radius rod is far too loose a fit in the motion bracket so I soldered a small washer on one side and a 12BA nut with the thread reamed out on the other. This ensured that it lines up with the reversing rod and was a close fit in the bracket.
The only other modification was to cantilever the return crank that fits to the centre driving wheel boss so as to clear the rods. This part is fitted by trapping it between the bush and the retaining screw. Once these details were thought out and implemented, assembling the motion was relatively easy, though some parts were only temporarily fitted.
This picture shews the complete motion, cylinders and motion bracket fitted and running on the rolling road. It is running very slowly but the picture was taken without flash to shew the motion in motion. Back to Top
The next job is to take the whole lot apart, clean it all up and paint the chassis before re-assembling, fitting the plunger pick-ups and final testing. By which time the body was back from Dennis.
Having got the motion running, "like a sewing machine", the time came to take it all apart again and paint the chassis. I experimented again this time with chemically blackening all these parts by first washing them all in very hot soapy water and rinsing carefully to get the oil and grease off.
They were then dried with a hair dryer and bathed again in a bath of neat Viakal. Several more washes in hot clean water and drying again with the hair dryer before plunging them into a bath of chemical blacking agent.
This worked well and the parts came out well blackened. Yet another wash and drying was followed by brushing the parts with an old tooth brush to get the residue dust off, don't breath it in, it's poisonous! The use of latex gloves here was useful.
Now that the parts were chemically blackened, the next task was to spray them with Halford's satin black acrylic paint, no undercoat was used. A single coat was all that was necessary and this provided an excellent finish that was thin and shewed all the detail. Should any part get chipped in future, it will still shew black.
Next, the motion was put back together along with, this time, the plunger pick-ups. These latter proved to be problematic. The frames are quite wide and it proved necessary to cut the springs for the pick-ups in half because they caused too much friction for the motor to run easily.
I think perhaps it may have been better to have used shorted out wheels on opposite sides of the engine and tender for pick-up. One odd omission from the kit was a draw bar though provision is made for bolting one in place. I made one from some copper clad glass fibre, which is bolted to the tender and engine drag beams so that they are semi permanently connected.
The time had come to put the chassis and body, recently received back from Dennis, together to see if the still fitted. It is a tight fit but goes together and works. Back to Top
Here is the completed engine parked in my workshop's private siding:
It has been an interesting project and I have, despite the problems and time constraints enjoyed it. A well designed kit that could be built by anyone with experience in etched kit construction.
The plate behind the coupling is wrong; these were not fitted until much later in life. However, the biggest howler is the dome being too far forward. No excuse for this, the picture clearly shews where it should be. In my haste I fitted it in the hole in the boiler, which is for the early, small dome. The NRM will release the engine in the autumn so that these errors can be addressed. So far, July 2012, I have not succeeded in getting it back to correct the mistakes so it may well live its life as it is.