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A web-site by Rob Speare

   

'Padstow'   -  A life long ambition reached with this West Country class.


A rebuilt West Country class 'Padstow' meticulously crafted by Bernard North.

Background to the Model

Being born and brought up in Brighton, Sussex, the Southern Region of British Railways was firmly in my blood.

As an ardent enthusiast, many happy hours were spent on the end of Platform 3 on Brighton Station, which was directly opposite the lines leading into the Loco Sheds.

Brighton Loco Depot (Code 75A) was quite a busy shed and the comings and goings of the various locomotives provided plenty of entertainment.

Along with some aged ex LBSCR locomotives and some more modern B.R. Standards, there was always a crop of West Countries allocated to Brighton Shed, used mostly on the daily run to Bournemouth, Plymouth and Cardiff.  Usually the ones allocated to Brighton were the original variety, but there was always a rebuilt version on shed visiting from somewhere on the system.

Occasionally some of the batch would be sent to Eastleigh for rebuilding, and replaced by a further batch of original locos, all except one.

This was 34008 'Padstow', a regular Brighton engine in its original state, which returned to Brighton again immediately after its rebuild.

My interest in railways and steam locomotives in particular, took me into the world of model engineering through the Brighton & Hove Miniature Locomotive Engineers, and their track in Hove Park.  Whilst still at school, I had started on LBSC's Juliet and had lots of ideas of what I would eventually like to build.  I went into engineering as a career, and ended up in the Bristol area working in both the automotive and aerospace industries.  I naturally joined the Bristol Society of Model Engineers of which I have been a member for 40 plus years.

My next locomotive after the Juliet was Martin Evan's 0-6-0 tank locomotive Simplex, which I painted in William Stroudley's 'Improved Engine Green' style reminiscent of the Terriers.  This locomotive has seen many years of active service on the Bristol Model Engineers track at Ashton Court.

I had finished my Simplex in 1976 and was looking for my next project which I wanted to be a large tender engine.  At the time, another of the Bristol members with a Southern interest was also considering his next project.  In a recent copy of the Model Engineer we had both spotted an advert for some full sized works drawings of a rebuilt West Country class.  I managed to get hold of the works drawings ahead of some of the preservation societies.

My mind was made up – I particularly liked the rebuilt version of the Bulleid Pacifics, and hence a natural choice for me was to build a 5in gauge model of West Country Class locomotive.  As for its name, the obvious choice was 34008 'Padstow' – it was a Brighton engine in both its original and rebuilt forms, and it was the locomotive I had seen many times at Brighton Station.

So this was the start of the project, long before the days of Keith Wilson's 'Ariel' design.  Incidentally, my colleague went on to build a 5in gauge model of Merchant Navy class 35003 'Royal Mail' also in rebuilt form.

The Model Design

The basis of the model design is the twenty or so works drawings that I had obtained back in 1976.  These have been a constant source of reference throughout the project.  Having obtained the drawings, I immediately set about producing my own drawings on A0 sized drawing film to 1 1/16in to 1 foot scale, on a second hand drawing board that was a throw out from work.  Most of the chassis was designed in this way and I have produced some 10 or so sheets of drawings covering all the chassis details.

Laterly, in the last 10 or so years, I have used AutoCad LT for all of the remaining design work, including the boiler and the tender.  I have also transferred most of the chassis drawings to CAD, and this is now my prime medium for design.

To supplement the drawings, I found it necessary to make frequent visits to look at a full size version to take photographs and make further sketches.  At the time, Woodham's Scrap Yard on Barry Island, South Wales was still full of locomotives including quite a crop of Bulleid Pacifics, and this was a useful source of information in the early days of the project.  More recently, I have visited most of the preservation lines that have Bulleid Pacifics.

Something I learnt early on was that Merchant Navies and West Countries are quite different machines.  Apart from the obvious differences, it is easy to think that many of the components are common, but beware - often they are not.

As the design progressed, I became aware that I still needed some further works drawings to complete the project, as there were some glaring omissions.  Fortunately, most of the drawings are still in existence at York Museum, and it was possible to get copies from their microfilms, which filled the gap.

Once I had the basis for the chassis drawn, I could not resist the temptation to start cutting metal.  I can't exactly remember when I cut out the main loco frames, but it was probably about 1978 - so the project was on the go for some 34 years including the drawings.

Locomotive Frame Assembly

The frames were cut from 1/8in mild steel plate.  This was before the days of laser cutting, and a band saw was used followed by milling and hand filing to produce the final shape.

The full size locomotive makes extensive of welded fabrications in place of castings.  This is replicated on the model by using steel plate silver soldered together, closely following the full size drawings.

The main horns are also welded to the frames on the full size with manganese steel facings.  The frames are positioned centrally over the horns which makes the distance between the frames narrower than normal.  In the model, the horns have been fabricated from steel blocks, silver soldered to frame plates.  Final milling to size was completed with frame plates mounted back to back.

Bogie and Trailing Truck

The bogie and the trailing truck assemblies also make extensive use of fabrications, again manufactured from steel plate, silver soldered together to replicate the original.  Full side control springing is provided using scale detail assembly.

Wheels

When the project started back in 1976, there were no castings available for Bulleid locomotives in 5in gauge scale.  So I had to set about making my own patterns.  As mentioned earlier, my colleague was interested in building a Merchant Navy, so we got together to get some castings produced.  Again this was before Ariel.

The wheels were a particular challenge;  I wanted to produce something that was reasonably representative with some of the undercut features, but without the complication of the complex pattern making of the full size wheels.

The solution adopted was to make the wheels in two parts.  The basic iron casting forms the general shape of the wheel with a 1/16th thick steel plate set into the front to form the external appearance.  Three patterns were required – Driving/Coupled Wheels, Bogie Wheels, and Tender Wheels.

After some filling and blending, the finished item bears a reasonable resemblance to the original wheels.  The photographs show the manufacture and the final result.

The pattern itself was machined from a billet of aluminium using the Myford Super Seven and a Dore Westbury Mill with a rotary table.  The castings were produced by a local iron foundry and over the years, a number of sets have been cast for other people with similar interests.

A similar process was adopted for the bogie / trailing truck and tender wheel castings.  In the case of the West Country class, the bogie and trailing truck wheels are the same size and could use a common casting, but reversed.  The tender wheel is slightly larger in diameter.

Axleboxes and Springing    

The main axleboxes are plain bearings made from cast iron to a split design to enable easy removal for maintenance.  In full size, main driver springing was by leaf springs, and my original intention was to fit leaf springs to the model.  A set of leaf springs were manufactured using a combination of spring steel and Tufnel strip.  However, the adjustment of the springs was found to be difficult in model sizes, and these have been substituted by coil springs.  This will enable the axle weights to be better balanced and hopefully avoid too much slipping.

Cylinders

The locomotive has three cylinders machined from iron castings, two outside and one inside blocks were required.  As I was in charge of the wheels, my colleague set about the patterns for the cylinders to my drawings.  Again, there were subtle differences between the Merchant Navy and West Country outside cylinders apart from just the difference in bore.  By careful adaptation, it was possible to make simple changes to the pattern to provide both versions.

The cylinders are piston valve using outside admission on the two outside cylinders and inside admission on the inside cylinder.  Cast iron liners were used lightly press fitted into the block.

The inside cylinder also forms part of the smokebox saddle and also carries the exhaust arrangement to the 5 jet Lematrie blast nozzle.  The arrangement of the steam exhaust differs slightly from the full size to make for easier assembly.

Exhaust steam from the two outside cylinders is brought together in a common cross pipe using typical model practice and then carried into a receiver cavity in the inside cylinder block ported to the base of the blast nozzle.

The bores of both the main cylinder and the valve liners were honed on assembly to produce a round and consistent diameter.  The piston valves are fitted with carbon filled PTFE rings energised with 'O' rings.  This has been tried with some success by others as an alternative to piston rings.  The main pistons and glands are also fitted with Viton 'O' rings.

The valves are mounted onto adjusting sleeve that allows the timing to be precisely adjusted and locked from within the front valve chest covers.

The drain cocks were manufactured from lost wax castings provided by Doug Hewson, the design being identical to the BR standards.

Lubrication is hydrostatic based on the Fred Cottam design.  The oil tank is under the footplate at the rear of the engine, while the sight feed glasses are between the frames, under the smokebox front.

Valve Gear

'Padstow' is fitted with three sets of Walschaert's valve gear adapted for outside admission on the two outside cylinders, and inside admission on the inside cylinder.  In full size, the outside cylinders are retained from the original design but the inside cylinder was replaced during rebuilding.

The model valve gear is to my own design based on the rules set out by Martin Evans and Don Ashton.  Over time I became interested in the nuances of valve gear design, particularly the properties of the expansion link backset in Walschaert's gear.  I had carried out a complete geometrical analysis of the valve gear, and calculated the backset from a series of equations.

When designing for the West Country, I got to grips with a BBC Micro Computer and developed a complete valve gear design package using my previous analysis.  This proved to be very successful, used for several other locomotives in the Bristol club, though nowadays it is contained in an Excel spreadsheet.

The valve gear design follows closely the full size dimensions, but is adapted in places to make sure the model will work successfully and (hopefully) efficiently.  The inside valve gear is quite different to the outside, being arranged for the inside admission layout.

Expansion Link brackets are steel fabrications, as is the screw reverser bracket;  this is driven by a gearbox arrangement in the cab via a rotating shaft and universal joints.

Smokebox

The smoke box is manufactured from a thick walled piece of hydraulic tube.  The original thickness was 0.375in, but this was machined down to scale outside diameter and the bore opened out to give a final wall thickness of 0,156in.

The chimney was turned from solid with a separate brazed on flange.  Suitable dressing brought the external appearance to the correct scale dimensions.  The blast arrangements are designed to incorporate the 5 jet Lemaitre exhaust nozzle.  The large diameter of the chimney and the petticoat pipe arrangement have been designed to provide the correct proportions for adequate draughting.  The size of the nozzles has been based on a typical single blast jet dividing the area into 5 equal jets.  This is yet to be proven in steaming trials.  The jets are removable to enable development to be carried out.

The smokebox door presented an interesting challenge as no castings were available.  This is again another unique feature of the Bulleid Pacifics that was essential to reproduce.  From the works drawing, I was able to determine the exact profile.  By doing a bit of geometrical analysis and using an Excel spreadsheet, I was able to calculate the profile of the door in 0.1in increments.  The embryo door started from a 6in diameter piece of free cutting mild steel.  Mounted on the Dore Westbury Mill and using a 0.375in ball ended cutter, I profiled the complete surface of the door in 0.1in steps in X, Y and Z co-ordinates.  This produced lots of dimples over the surface at each co-ordinate point.  These were then blended using a file to produce a smooth surface, very close to the correct profile.

Boiler

The boiler design is to my own drawing, but heavily based on Keith Wilson’s 'Ariel' design with some slight modifications from Les Warnett's 9F boiler.  The main changes are the slight reduction in length and grate area to fit the scantlings of West Country boiler.  The tube arrangement is exactly to the 'Ariel' design.  All of the plate thicknesses and tube diameters are the same as 'Ariel'.

The stays are copper rivets silver soldered in place.  The crown stays are headed rod type stays as are the cross and longitudinal stays, again all silver soldered.

The boiler construction was a joint effort between myself and Peter Carr from Kingswood Boilers.  Basically, I did all of the manufacture of the component parts, plate flanging, bushes etc from material provide by Peter.  I did the 'dry' assembly where necessary using rivets as guided by Peter.  Peter then did all of the silver soldering including the staying.  The boiler was completed before the CE marking regulations came into force.

The boiler was hydraulically tested by the Bristol SMEE boiler inspectors to 180psi for a nominal working pressure of 90psi.  It passed first time with not a single leak which is testament to Peter's excellent silver soldering.

Boiler Fittings

The boiler fittings are a mixture of 'Ariel' and my own design.  The steam turret, regulator and water gauges are straight 'Ariel' design.  The brake valve is of my own design as an approximation to the full size Davis and Metcalf version.

The firebox door is a key characteristic of Bulleid locomotives and I have reproduced this very close to scale from a works drawing of the Ajax fire door.

The water feed is from two injectors of standard model design purchased from Polly Engineering.  These are mounted under the drag beam at the rear of the engine.  One feeds directly through to the pipe work to the front of the boiler.  The second feeds through a dummy injector under the right hand side cab window.  This is manufactured as a close replica of the real injectors complete with stop valves for steam and water.  In fact it is just an elbow in the feed to the front of the boiler from the model injector.  Time will prove if this is successful in operation.

The only other form of water feed is from a large double acting hand pump in the tender.  There is no axle pump fitted.

The clack valves mounted up on one side of the boiler are manufactured from Doug Hewson's lost wax castings as used on the BR standards.

The drain cocks are steam operated though a convention valve located by the driver's seat in the cab.

The superheaters are stainless steel radiant type with return bends welded by Trevor Tremlin at Swindon Boilers.  The fabrication of the steam pipe connections inside the smokebox was done by myself.

The pressure gauge is a standard model type gauge purchased from Polly Models.  A red line has been added at 90psi as the working pressure.

The ashpan is again a scale replica of the full size version directly from the works drawing.  The grate is a conventional model type manufactured from 1/8th stainless steel strip.

Boiler Clothing

The boiler clothing is manufactured from 26g brass sheet and is assembled as a continuous sleeve.  A noteable external features include a complex 'bubble' that covers a stop valve for the steam feed to the steam turret on the backhead.  This feature on the model is dummy as it proved to be too difficult to route a reasonable sized pipe to the backhead.

There are many dummy 14BA bolts over the surface positioned as per full size primarily to hold together the various sheets of the clothing.

Among the challenges were the separate pieces of clothing over the stop valve, and the steam pipe feeding the backhead.

Handrail knobs and boiler washout plugs were all manufactured by myself.

Padstow's Cab

The cab is fabricated from steel sheet silver soldered together.  The construction follows closely the full size design again from the works drawings.  An opening slide out piece provides access to the backhead controls for a comfortable driving position.  The layout of the cab is a compromise between full size and practical operation of a scale live steam model.

The cab windows are made from a close grained hardwood stained to look like the original frames that were mahogany.

Under the cab on the left hand side is a dummy steam turbine generator.  This has been closely scaled from measurements of the full size version – a drawing could not be found and hence lots of photographs and sketches were required.

Attached to the drivers side of the cab is the reverser gear, mostly fabricated by myself but using some of Doug Hewson's lost wax castings.  The reverser gear drives the screw reverse via a rotating shaft along the side of the firebox clothing.  The universal joints were purchased from RS components.

Transfers on the cab sides were obtained from Fox Transfers.

Platforms

The platforms (or running boards) along the side of the engine again closely follow the full size version from the works drawings.  Dummy lubricators are provided on each side of the engine.  These lubricated many points along the engine including axleboxes, and cylinders.  The dummy lubricators were fabricated from sketches and drawings of the full size versions.

The nameplates, smokebox number and shed code plates were manufactured by Alan Gettings (the former owner of Diane Carney's nameplate business), fitted to home made backing plates.

Also mounted on the left hand platform is the Smiths Speedometer Drive.  Although a dummy, it is a scale representation of the full sized parts.

Locomotive Brake Gear

The locomotive brake gear is a clasp design with two brake shoes per main driving wheel, and is fully compensated with adjusting links between the middle and rear drivers.  The locomotive brakes are steam operated and steam cylinders are provided between the frames.  The brake gear is fully compensated with adjusting links between the middle and rear drivers.

Tender Chassis

The Bulleid Pacifics were fitted with a range of different tenders and care is needed to select the correct version for the actual locomotive being modelled.  34008 Padstow was fitted with the 4500 gallon tender for most of its life as attached to this model.

The chassis again makes use of many steel fabrications.  No castings, apart from the wheels are used on this model.  Components were either fabricated or machined from the solid.  The SR lettering on the side of the axleboxes was a thin etched brass plate also produced by Alan Gettings, soft soldered to a brass front piece on the axlebox.  The leaf springs are manufactured from spring steel and Tufnol leaves.

The tender brakes on the full size locomotive are vacuum operated.  On this model the arrangement is dummy, but the screw hand brake is operational.

Tender Tank

The tender tank is constructed from brass sheet soft soldered together.  Internal frames are provided at the correct locations to help with the profiling of the side sheets.  The tool cupboard and roof section is removable to allow access to the controls for driving.  A large double acting hand pump is fitted to the tender; to access this, the vacuum cylinder section can be lifted off.

The small filler cap to the right of the main tender filler cap is for the TIA water treatment.  In full size, special briquettes of chemicals were added through this cap to treat the water and extend the time between boiler washouts.  The lights fitted to both the tender and smokebox are dummy.

Paint Scheme

The locomotive has been painted throughout using Precision Paints synthetic enamels.

In general, their two pack etch primer has been used both on steel and non ferrous parts.  The BR emblem transfers on the side of the tender were also supplied by Precision Paints.  The 'ex works' paint scheme is based on British Railways West Country paint scheme of 1957, where the main colour is BR Post 1954 Loco Green lined out with orange and black.

A Badger air brush has been used for most of the painting, while a lining pen produced by Bob Moore was used for the lining out.  As always with paint schemes, there were local variations and some running sheds added different features depending on the Paint Shop foreman at the time.  For instance, some had guide bar brackets and inside motion painted red,  some had painted wheel rims on the loco; while others did not.


Finale

This locomotive represents almost a lifetime's work for me with lots of highs and lows along the way.  I am pleased that at last it is finished – if ever anything like this is ever completely finished – there is always one more job.  The Bulleid Pacifics are quite complex machines and have a significant number of unique features that identify the breed.  I hope that I have captured a reasonable representation of the Rebuilt West Country class complete with some of Bulleid's original features whilst producing a working live steam model.

At the time of writing, the locomotive had not been steamed, but it has run many hours on compressed air at Bristol exhibitions in the past.  Once the initial steaming teething troubles are sorted out, it hopefully will be put to useful work on the Bristol SMEE track in Ashton Court, and on other tracks around the Country as the opportunity arises.

Now perhaps I can get on with something else, not quite so complicated !

    Multum in Parvo     -   Bernard North