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Building the Aster 9F

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.


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 that a conversion to a single chimney for a black kit may not be too difficult though this will NOT be an Aster modification! 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 both 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. This was not the only tender fitted to 9Fs; the others being the 1B type for Crosti boiler versions of the loco, 1C type for LMR use, 1F type for ER use and 1K type as specially fitted with the experimental mechanical stoker. The modification of the Aster tender to any of these other types would be a significant task with everything above the chassis needing to be renewed. Should there be sufficient demand, there may be someone prepared to provide the necessary frets to make this possible. 

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. 

I was very excited by the arrival of my kit in mid December. Work began almost immediately to the tune of my wife’s protestations that ‘surely Christmas should be celebrated first’. I reluctantly gave in but couldn’t resist regular visits to my workshop to examine the contents of the box. The result was a completed loco by 2nd Jan 2008!  

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. 

The kit arrives in the usual very strong box with most components separately boxed and packed in 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. I found very few drawing errors in the design and those discovered have been notified and are pointed out in what follows. Section 1 builds the main chassis construction 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 may be a little awkward and an extension of the Pt. 34 may well be an advantage.  

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 make a change; I always 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. 

In Section 4 the valve gear is assembled and here I would 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 alignments are correct, enabling the fitting of the 5-18 pin much more easily. I do recommend you use your finest file to smooth the inner surface of the expansion links to ensure the die-block moves freely. Polish them rather than remove enough metal for a rattle! Otherwise careful fitting in this section will ensure smooth operation of the expansion links. 

Examine Section 5 drawings carefully and be sure you understand how the valve adjustments work. Note that there appears to be an error in this drawing in that the counter bore in the inner face of the cylinders seems to be cut for the fitting of PS3-1.9 rings and not PS4-1.9. This is the subject of further investigation and whilst Markus Neeser, Geoff Calver and I have all shown that the PS3-1.9 rings work perfectly, Aster have been consulted and are still insistent that the PS4-1.9 is the correct ring to use!

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.  

Having achieved this, in Section 6 you must next 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 or any of the blow-by said to have been experienced by some builders. 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. 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 [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. 

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 with the double 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 superheater to the main steam pipes and lubricator and yet making the lower attachment bolt 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. Again I always fit a nitrile ball for the clack here. 

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!  

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 and 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 23 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 will be needed. It remains to be seen whether I’m right. There is nearly always room for adjustment here I find! My pal Geoff Calver always substitutes the Canadian Super Wicks but I haven’t had a problem with those provided to date. 

The tender is a very straightforward build and there is a little on which to comment other than on its beautiful construction and finish. Again nitrile balls were fitted to the pump clacks. 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 of the assembly I’m sure you will be as delighted as I was as the 9F really is a very splendid model and will probably prove to be the best runner yet. Those of us conversant with the Aster line of models already believe it to be the most detailed yet attempted by the factory and quite magnificent. 

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. 

When I notched up I was astonished to discover that I could get it almost up to mid position before it became rough. The regulator was gradually moved up to fully open to maintain the same revolutions as near as I could judge. This is by far and away the best I've ever been able to achieve from my other Asters including the Spam Can, Duchess and King none of which were able to better 5 to 6 turns notched up. I stopped the engine and reversed the mechanism and opened the regulator again and off she went. I was able to notch up in reverse just as far as in forward gear!

A few days later the winter weather here in Cornwall cleared for a few hours and I was able to run it at a friend’s track which is a small oval with curves of constant radius of about 3 to 4 metres. It was extremely cold at about 3 deg C. but there was no wind. The fire was a little difficult to light because of the poor access to the burners but it was soon ignited via the gap behind the rear drivers, the flame spreading forward from the rear without removing the fan.

It took 5 minutes to safety valve blow off and at that point I cracked the blower open slightly after removing the fan. The blower seems very powerful and I only needed a touch to make the fire roar. I next opened the drain cocks followed by the regulator and for about 15 feet there was a squirt of water from the drains but none at all from the chimneys which was a delight. I then closed the drains and she was off lightly loaded with just 5 opens and a NE guard's van.  

Throughout the run I had the by-pass almost closed and the engine ran with a drift of steam from the safety valves. After about 5 circuits it was obvious that the engine was already very free running and I added several more opens and vans to make a load of around 15. There was very little difference to the sound from the exhaust and hardly any more regulator was needed. This engine is going to take a huge load! 

I stopped the engine twice in 55 minutes for a general look around and to refill the tender. I found no loose or damaged fittings and the only small incident during the whole run was a short period of priming when my attention strayed to a cup of coffee when I needed to open the by-pass valve. 

I didn't try running the engine in reverse again but I see no reason why it should not have been just as successful. On shut down there was an almost full oil tank of condensate and only the merest sign of oil in the chimney. Just right and no signs of the gulping sometimes experienced with slide valve engines! 

To say I'm delighted by the engine is an understatement. In my view it is the best yet and I'm confident that the biggest single contributor has to be the new valve gear design. Now I need to keep the Chinese water treatment up on Andrew in attempt to get him to make a GW engine happen next. A 28XX would be just wonderful! 

Note: The 9F kit has steam heating pipes included for both Evening Star and 92214. The lost wax casting includes both vacuum and steam heating pipes at either end of the one casting. If you want to be strictly correct you will need to cut off the steam heating pipes from both engine and tender for Evening Star but only from 92214 if you are modelling it in BR condition.

Permission to post this article by Dave Stick on the Southern Steam Trains website has been graciously granted by the author, Dave Stick.  Also, we express our thanks to Nick Rudoe and Peter Trinder, Editors, Gauge 1 Model Railway Association’s Newsletter and Journal.  Originally published in the G1MRA Newsletter and Journal (Issue 217) Spring 2008.  Also, our gratitude to Andrew Pullen, Aster Hobbies (UK) LLP for facilitating our communication. 




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