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Building the Aster 9F  /  2018 Revised Edition

By David Stick


Back in the summer of 2007 Aster UK distributor Andrew Pullen announced the new British outline model from Aster. Much to most people’s delight it was to be a 9F – that was great news for those of us who had been pleading with Andrew for one of these for some time. 

After the railway nationalisation in Britain in 1948 and as a result of the publication of the exchange trials conducted shortly thereafter, the need for a new large freight engine was announced. It was shown that what was required was a design with greater boiler capacity than previously available capable of sustaining higher speeds both on the level and in hill climbing. For some time the team doing the studies recommended that the new loco should be a 2-8-2 but, after much argument between Robert Riddles, Chief Mechanical Engineer of the Railway Executive and E. S. Cox, Chief Officer, Motive Power, a volte-face resulted in a 2-10-0 being chosen in 1951. The subsequent release of 251 of these fine locomotives starting in late December 1953, was to prove the worth of the studies. Much as these two gentlemen led the planning phase, the development and production of these locos was attributable to others in the engineering team. The 9F’s success was largely due to the locomotive design staff in Derby under the leadership of Frank Carrier. The detail design work however was conducted in several of the surviving design centres of the old constituent companies of British Railways and was therefore a national team effort and something of a magnum opus for British steam locomotive design.   

Hence it is very gratifying that Aster should have made such a beautiful job of scaling their new model. The initial photographs of the prototype released showed that it was to be a model of 92220 Evening Star in its fully lined-out Brunswick Green splendour as seen at the National Railway Museum in York. However, Andrew was quick to announce that there would also be an alternative black version modelled on 92214 which is, of course, another preserved loco whose restoration was completed at the Midland Railway Centre at Butterley in Derbyshire. Both versions being products from Swindon Works. 

As more photographs were released it became apparent that we were about see another step forward in both technical detail and fidelity to the original design. Firstly, there were to be piston valves replacing the usual slide valves, a first for Aster. Next there would be cylinder drain cocks only previously seen on a few foreign models at the more expensive end of the Aster market but pretty well essential for an engine fitted with piston valves. It also became obvious from the photographs, and later the drawings, that the fully reversible valve gear was to be a close copy of the full sized mechanism of the wheel type mounted in the correct plane. 

In most other respects the engine represents a further development of the well tried and tested design and construction. It includes a very rigid, cross-braced and fully sprung chassis with flangeless centre drivers as per the original and is fitted with an axle driven pump. Onto this is mounted a large C type boiler with blower and superheater of the usual design. Both of the models to be produced have a double chimney as fitted to their big brothers when built at Swindon. A first look at the design of the front end of the model suggests the possibility of a single chimney version and this has now been produced by Aster/Accucraft as a later batch. The boiler casing is beautifully detailed with all the ‘bells & whistles’ showing and includes a dummy representation of all the external boiler mountings as far as I can see. The cab is glazed too, another first for a British outline Aster.  

The tender used for the early batch of Aster locos is the BR 1G type as designed for use on the Western Region of BR. Full sized, it had a capacity of 7 tons of coal and 5000 gallons of water. The second batch tender is to the BR1C design of the high-sided type as produced in Crewe for the London Midland Region.  

Other than the features mentioned above there are few variations between the locos. But as usual if you want to build a representation of your particular favourite you must obtain a good photo and work from that. Good sources of both photos and history can be found in two specially recommended volumes – Richard Derry’s ‘The Book of the 9F 2-10-0’ published by Irwell Press and the out of print ‘The British Railways Standard 9F 2-10-0’ by Philip Atkins also from Irwell Press. 

It became immediately apparent that a kit with this level of sophistication and complexity was going to need very careful study of the drawings and rigidly sticking to the recommended build sequence. What follows are my notes taken from what I discovered during the build and where considered necessary, to offer tips on construction as I have done before. I do not intend to suggest in any way excessive difficulty but rather the need to remember how to eat an elephant – one mouthful at a time! 

There are no special tools or equipment necessary for the construction of this kit. Reference to earlier articles that I have written for the Journal and elsewhere will show what I use. Once again I do recommend the acquisition of a set of three hand broaches as used by the clock makers. These are used to ease tight holes usually caused by an excess of paint. In addition, I recommend that builders will find benefit from having taper taps in M1.4, 1.7 and 2 mm size again to clear threads that may have been partially blocked with paint or swarf. 

The kit arrives in the usual very strong box with most components separately boxed and packed in tissue paper and bubble wrap. Care should be taken to only unpack those components needed for the task to be undertaken. Check the parts against the inventory provided and the excellent drawings. Section 1 builds the main chassis and is fairly straightforward. Note that the stars shown on 4 bolt holes indicate the use of countersinks and are on the outer faces of the frames. Build the frames on a thick glass plate and test regularly to ensure that there is no transverse or longitudinal rock. If there is you must adjust the assembly to bring the chassis true, hence ensuring that the axleboxes will not bind. Remember to use a fine file to finish the running surface of the cross heads to ensure smooth contact with the slide bars. I’m of the opinion that access to the cylinder drain cock operating lever locking set screw is impossible after the boiler is fitted. Care should be taken to make sure that the thread UNDER the operating levers is used for the grub screws. They are then easily reached with the loco inverted. I recommend that Loctite 222 or stronger be used. 

Section 2 installs the wheels, axles and the axleboxes. Before fitting each however, the counter-weights have to be fitted to the wheels. It is important to examine these weights carefully as the outer ones are in a package with yellow marking and the blue ones are the inners and are thicker than the outer. If you put them on the outside you will find that the weights foul the rods! The Inners have countersinks on their inner faces to recess the heads of the long screws. The screws which do not have countersink heads retain the weights in place and the screw tails are flush with the weights’ outer faces. Hence they are only just long enough and if you don’t have the countersink on the right way around the bolts will appear to be too short!  

Before you fit any of the wheel sets first install the two Pt. 16 weights to the chassis as you will be unable to fit them with the wheels in place. Also, note that the dummy brakes are not fitted until Section 3 when the axle pump is assembled and fitted. Here I usually make a change; I fit nitrile balls to the axle pump clacks as I find these never let me down, something that I cannot say about the s/s balls provided in the kit. Though it should be added that later balls delivered in kits seem to be better. The option is yours. 

In Section 4 the valve gear is assembled and I would first recommend that you get your taper taps out and run through all of the threads to make sure they are not too tight when pins and screws are fitted and avoid the possibility of a screw or pin seizing!  I would also recommend that you dive into the Section 5 package and extract the Pt. 5-11 and 5-18 pin first. I found it much easier to fit these to the Pt. 4-16 before assembly of the latter to 4-15. If you do this now you can ensure all alignments are correct, enabling the fitting of the 5-18 pin much more easily. It may be necessary to ease the holes in the chassis through which the weight shaft 4-14 slides if it is considered too tight. 

Next use your finest file to smooth the surfaces of the die blocks and expansion link inner radii. These have been manufactured using laser cutting and the rubbing surfaces need cleaning up to reduce friction between them. Careful fitting in this section will ensure smooth operation of the expansion links that is essential. 

Examine Section 5 drawings carefully and be sure you understand how the valve adjustments work. Note that the dimension given for the length of the reach rod is a nominal figure of 181.7 mm and some small variation will result during the valve setting process. This will occur when adjusting for the correct position of the die block in the expansion link. Also note that though the drawing says that it is important to make parts 4-11 and 4-16 appear in phase it is only practical if tolerances allow. Rather, it is imperative to ensure that with the reverser set in the mid gear position, both of the die blocks must be exactly half way down the expansion link.  

In Section 6 you aim for equal Laps 1 and 2 and separately, S1 and S2. This is achieved by varying the length of the valve rod Pt. 5-6 by using a screwdriver in the front of the valve. To achieve this you must have locked the threaded end of the screwed rod INSIDE the valve first using a thread lock. When assembling initially you set the valve rod to 9.5 mm between the back of the valve and the fork end nut. You then loosen the nut to allow the adjustments to be made. Rotating the valve with the screwdriver in the slot in the end of the valve will lengthen the distance set nominally at 9.5 mm. This will vary as the valve is adjusted to give the correct Lap1=Lap2 and S1=S2. On my example Lap1=Lap2=2 mm and S1=S2=3 mm. Air testing will prove whether you have the valves correctly set. 

My air test was completely successful and showed no leaks from either the cylinder drain cocks. I always soak my pistons in steam oil with the rings fitted prior to fitting to the cylinders. But even if this isn’t the whole answer, after a short period of running with live steam in the cylinders the rings ‘swell’ and no further blow-by will occur. 

There are no difficulties in Sections 8, 9 and 10 but don’t forget to keep the nut on the lubricator pipe raised when installing the saddle in Section 9. It is important to make sure that the oil pipe is always sloping upward to ensure a good oil feed.

Before fitting, polish the dummy drain cock castings using a small brass wire brush to obtain the right finish. Also, I would recommend adding a small washer on the shaft of Pt. 9-13/14 behind the Pt. 9-15 dummy Mechanical Lubricator. This will prevent the shaft working in and out of the bearing in what is a very delicate assembly. I hope Aster have lots of spare Pt. 9-17 operating rods!  

As an interesting aside, whilst visiting the West Somerset Gala a few years ago I had a storming run behind 92214 from Bishop’s Lydiard to Minehead. I went down to chat to the driver and whilst talking I drew his attention to a badly bent operating rod [the full size Pt. 9-17]. A fitter was called and it was found to have been caused by a very tight fit in the rod end bearing causing a partial seizure. It could have been expensive if not fixed! 

Building the boiler assembly is straightforward and the only note I would add to Section 11 is to ensure that when you fit the regulator you should engage the thread at the backhead end of the boiler far enough to ensure that the restrictor Pt. 12-10 can be fitted in the centre of the access hole in the top of the boiler. Use your new pump handle provided in the kit to centre the upper and lower water gauge fittings Pts. 12-2 and 12-7 before inserting the glass. Since I always drive my engines from the left hand side where possible, I fitted my regulator handle at the 9:00 o’clock position and not the 3 shown in the drawing.

It’s helpful to anneal the pipe 12-4 before fitting as softening it will make bending it to the correct shape easier and avoid kinking. 

The subject of boiler insulation should next be considered. I always fully insulate my boilers and I did so again this time. Aster don’t provide enough material to do this in the 9F kit and additional material will have to be purchased from one of our suppliers. I make up a paper template and use this to avoid wasted insulation material. This can be ‘faced’ with a sheet of baking foil for added advantage and greater efficiency. The dressing of the boiler outer casing or cleading is fairly straightforward though care needs to be taken to avoid damage to the beautiful paintwork. When installing the inner boiler to the outer casing take care to ensure that you have the front ring Pt. 14-1 properly fitted with the holes in the right position. Check against the saddle and smoke box casing.  

In Section 15 be careful to align the superheater and blower assemblies so as to have correct alignment of the blower with the chimney. This may need adjustment later but will be very difficult after closure of the smokebox top half. When fitting the boiler assembly to the chassis, be careful to align both the superheater header to the main steam pipes and lubricator and yet making the lower attachment bolt M2.6-6 locate correctly. I recommend loosening the boiler to backhead plate bolts to make it easier to fit the two locating M2-4 support bolts at the bottom edge. Be quite sure that when you fit the Pt. 16-6 water connection bolt that you have the correct one with the slotted end.  

Cab assembly and fitting in Section 17 is without difficulty but note that the dummy reach rod guide is not fitted until Section 20 by which time you will have got used to fitting 1.2 mm screws! Note also that the reach rod 20-2 is only just long enough to mate with both ends and I used an epoxy glue to hold it in place. 

Section 18 goes without significant problems but note that the disc of insulation fitted to the inside of the smokebox door is 50 mm in diameter not 60 mm. When fitting the smoke deflectors in Section 19 make sure that the upper supports Pt. 19-1/2 are the right way round. The gap between the middle leg and the back leg is the shorter. Before bending the copper pipes Pt 19-9 anneal them to make bending easier but remember to polish them afterwards to remove the inevitable oxidation. 

All pipes and wires should be bent to shape using the scale templates at the back of the drawings. No annealing was found necessary for these as they are of smaller diameter. The wonderful casting provided to simulate the injectors and associated pipes on the right hand side under the cab needs careful polishing with a small wire brush to reduce the too bright finish. I use a gun blue to make the finish look more weathered and realistic. The valve bodies should be painted satin black. 

Much to my surprise the burner for the 9F has smaller diameter tubes than I expected. I have fitted 25 strands of wick material to each tube and they protrude from the top by 13 mm which is my own assessment of what I think is needed. There is nearly always room for adjustment here I find and your fuel and operating conditions may vary. 

The tender is a very straightforward build and there is a little on which to comment other than on its beautiful construction and finish. In Section 24 don’t fit the dummy pipes to the 24-1/2 strainers until after fitting the horn-cheeks and axleboxes as it hinders access to the fixing bolts. 

On completion the next step was a run on the rolling road where it worked perfectly straight off. There was no blow-by from the pistons or the valves and no leakage from the drain cocks either. I ran it for 50 minutes on one tank of meths and it consumed 2 1/2 tenders full of water. Each time it was filled up to just under the by-pass return pipe. I thought this a spectacular performance straight off the work bench.





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