Cheltenham Society of Model Engineers

After completing my first steam locomotive (a 5"Gauge GWR Pannier Tank) I soon realised just how heavy these finished items can be. Help would be required to move it around (especially if I still wanted to be moving it around in 5 to 10 years time). So that I could 'go for a steam' on my own I decided that my second project would be a 3.5"G locomotive. I also thought that I would try building a pair of locomotives, selling one to recover some of the cost.

The LBSC designed Pannier Tank had been successful, so another design of his should be OK. The GW 'Hall' Class locomotive, marketed by A.J. Reeves, was selected.

However, one look at the plans and its general appearance left much to be desired.

LBSC General Arrangement View

There certainly appeared to be something wrong with size/position of the smokebox and height of the chimney.

From the GA picture and the photograph above one can easily see that the cylinder steam pipes should be set back from the centre of the smokebox and not in the centre, as depicted on the LBSC GA.

A copy of the actual 'Modified Hall' front end drawing was obtained from Oxford Publishing (I don't know whether they are still around). The dimensions and position of the smokebox were scaled from the drawing and chimney dimensions scaled from drawings of standard GW chimneys. A PC CAD package was used and the separate piece parts (smokebox, chimney etc) were drawn as individual items.

GWR General Arrangement
(Not the 'scaling' drawing)

The boiler drawings were amended to take account of the smokebox changes. Connecting and Coupling rods were fluted and 'fish-bellied', respectively. All piece parts were drawn on the pc and the individual drawings were then 'assembled' to produce a new General Arrangement drawing.

New General Arrangement View
(Incomplete)

'Assembling' the parts together onto a new GA drawing was an ideal way of ensuring that the individual parts were the correct size. Using this technique it was found that the rear section of the Coupling Rods was incorrectly dimensioned by 0.0625".

One distinguishing feature of the 'Modified' Halls is the front bogie which has a plate construction. LBSC uses a casting for both the front and back of the bogie, and on the front at least, this looks completely wrong. The bogie is also short by about 0.0625". Strictly speaking the front of the bogie should be level with the front of the buffer beam. Because we use 0.125" angle for the beam, as against a scale 0.0625", the bogie needs to be increased by a total of 0.125" in order to line up.