Construction of a model Bulleid Light Pacific: West Country Class Locomotive No. 34008 Padstow

Quick links

Photos of Finished model

Final stages

Wheels

Chassis P1
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decisions

Chassis P2
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mainframes

Chassis P3
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coupling rods
- updates for motion, self-powered, bogie & pony truck

Body Part 1

Body Part 2

 


Images of 7mm scale plates produced by GUILPLATES - not to scale

Introduction
Padstow was built by the Southern Railway at their Brighton works and entered traffic on 10th September 1945 with the Bulleid style running number 21C108. From new, it was shedded at Exmouth Junction and employed on the Devon Belle service, west of Exeter. It became BR loco No. 34008 at the time of its 'Light Causal' overhaul in March-April 1949. At its following 'General' overhaul, April-June 1950, it received a 'wedge shape' cab. It was transferred to Nine Elms shed on 11th April 1951 to be employed on WoE and Bournemouth / Weymouth services.


Photo of finished model - see below

On Wednesday 20th August 1952 Padstow pulled one of the Devon Belle stock special excursions to Dorchester, Dorset. The train came on to Weymouth for the turning of the loco and the Pullman Observation & Bar Car. It is the condition of the loco when it hauled this special excursion that I have chosen for my model. The salient features are shown on the following photo, of a sister loco.

These being full Air-Smoothed casing with (A) valance panels forward of the cylinders, (B) removal of the leading brake shoe, (C) no slidebar cover, (D) blanked-off front sanding, (E) fairing to the rear of the chimney, (F) original safety valve arrangement, and (G) modified cab.

 

 

  Final Stages - 9th Oct 2011


Not finished, but getting there!

The target is to have completely finished my model by the 31st October 2011 which will be the 66th anniversary of its naming ceremony. Recent work on model

 

1 Sept 2010 Construction begins - 65 yrs after the prototype  
  Preparation of the wheelsets  
 

Wheelsets assembled and in nominal position

 
 

I'm using Slaters wheels that are supplied in a flat-pack form that contains a pair of wheels complete with axle and wheel retaining (countersunk Allen) screws. Driving wheel packs also include crankpin 12BA screws, bushes, washers and nuts; these are contained in a plastic tray sealed with Selotape. Also, in the above photo are the tools required at this stage. These are a modelling knife with the ubiquitous acute angle blade, a small flat file and an Allen key. The file is needed to 'clean-up' the square ends of the axle; a snug fit is required for the wheels, not too tight as the wheels can be on and off quite a few times before completion of the model.

 
 

Before assembling wheels on the axles it is necessary to remove the small moulding excess close to the rim. In the above photo the small excess can be seen at 9 o'clock on the back of the right-hand wheel; it has been removed with a sharp (modelling) knife on the left-hand wheel - see nominal 3 o'clock position. The axle with retaining screws and the items constituting the crankpins, are on the left in the photo. Here's the Slaters GA drawing...

... and here's the assembly underway:-

From the left in the above photo, crankpin components, wheel with crankpin assembled, and axle fitted to one wheel. Note the 12BA nut holds the steel washer and brass top-hat bearing solid on the wheel; the bearing surfaces for the motion rods being the combination of the steel washer under the nut and the brass top-hat. For the coupling rods, the top-hats have to be reduced in length, to the thickness of the rods plus working clearance. The centre wheels require a further top-hat bearing for the connecting rod, again reduced in length to the thickness of the rod plus working clearance.

 

 
2 Sept 2010 Chassis phase 1  
 


'Here's one I made earlier' - it belongs to my model of 34064 and is virtually identical as far as the principal components are concerned


Here's the starter for 10, the etches: chassis frames, motion rods, bogie fames, and parts to form the cylinders and motion brackets.

Note in the above photo the tools employed at this stage, namely a pair of small (and sharp) side-cutters and a small flat file. The side-cutters are used to carefully separate the various parts, and the file used to remove the excess metal at the attachment points.

Here's some more views of 34064's chassis, with 34008's frames alongside:-

Before assembling the basic chassis, more decisions were required, these are as follows.

  • Electric Motor & Gearbox unit. From previous experience, I've chosen to use the same unit as in the two Bulleid Pacifics I've built i.e. a Crailcrest motor and MSC 14:1 2-stage gearbox. These are particularly bulky power units and, in O-gauge, there's not many locos that afford the room; Air-Smoothed Bulleids being one of the notable exceptions. The performance from these units is really first class in terms of low-speed running and pulling power, as well as a very respectable top speed, again with an amazing amount of power. I haven't come across a better power unit, for O-gauge!

  • Driven axle. The real issue here is whether the chassis is to be compensated. From personal experience, I've found compensation on locos to be a luxury that can be dispensed with, in the name of free-running. However, 3 rigid axles affords far from satisfactory running, mainly due to poor electrical pick up - never much more than 3 (out of 6) wheels in electrical contact with the rails, at any one time. The overall performance of my 34064 is a powerful reason for me duplicating its drive and electrical pick-up arrangement - see later.

  • Electrical pick up. On my previous Bulleids this has been a bit of an afterthought, so for 34008 I thought I'd plan ahead and use Slater's plunger pickups.


The motor position is an over-riding consideration - everything has to fit around it

The above photo shows one frame marked-up with the position of the gearbox and the rim of the driving wheels. Also marked are the positions for the plunger pickups. Whilst the positions appear very close to the edge of the wheel, it has to be born in mind that the rims have a Vee insert for the (electrically dead) centre moulding, to prevent rotational slippage - see back of the wheel rim at 6 o'clock, above. The above photo also shows markings above and below the centre axle bearing (etched) hole; when the holes are opened-out to the markings, 1.5-2mm of movement is provided for the centre axle's bearings. This movement allows a minimum of 4 wheels to be in (electrical) contact with the rails. A slight downward springing will be provided for the centre axle to ensure (electrical) contact of the wheels; importantly it will overcome any tendency of the spring plunger pickups to lift the wheels. Finally, note the business end of a reamer used to ease the holes in the frame for the brass top-hat axle bearings and the axle bearings themselves.

All that remains is to drill pilot holes for the plunger pickups; I've elected to include an optional position for the centre driving wheel, as I shall be fitting additional stiffening to the chassis in the area of the gearbox. Note an Engineer's Clamp used to stiffen the two frames, which are bolted together, whilst the holes are drilled using a mini-drill.

Constructions continues on separate pages - see 'Quick Links' at top of page