It was triggered by a post on @Annie’s thread about modelling one of the B&ER 4-4-0ST engines but now I’m not sure whether this is the prototype I want to model. While thinking about the possibilities, I came across an appraisal of Broad Gauge 4-4-0ST engines in an early issue of the Broad Gauge Society magazine ‘Broadsheet’ [No.17, Spring 1987].
The ‘Broadsheet’ article pointed out that there were 96 of these engines, all derived from a design by Gooch, originally created to meet an urgent operational requirement on the South Devon Railway, following failure of the atmospheric system. The first two engines, built in 1849 set a pattern for all these engines, in that the leading bogies swivelled on a ball-and-socket joint attached to the bottom of the boiler. The boiler provided the only structural link between the cylinders and the main frames, which terminated at the leading coupled wheels, although some later versions had full-length frames.
In order to help modellers, the article divided the engines into four main groups, as follows:
1. GWR and SDR ‘Short-tank’ Engines : together with the first two by Gooch, there were 27 engines in this category, from many different builders. These engines remained substantially as built throughout their working lives, except for the addition of weatherboards, modified front foot-plating and, it is believed, circular smokebox doors.
2. SDR ‘Long-tank’ Engines : there were 16 engines, widely known as the ‘Hawk’ class, which were initially hired by the SDR from contractors. In 1866, the SDR purchased all these engines and ordered 6 more from the Avonside Engine Co. These later engines had full-length plate frames. A further 4 engines were built in 1872 and 1875, designed to be convertible to standard gauge, although this was never carried out. Two of these engines actually outlived the Broad Gauge, when they were used to shunt BG stock at the Swindon ‘dump’ until 1893
3. Bristol & Exeter Engines : There were 26 engines in this group, generally more standardised than the SDR engines. Although attributed to James Pearson, the engines followed the Gooch design quite closely but with full-length main frames and a very long (9’ 2”) coupled wheelbase. Access to the footplate on all except the first six was over the top of the rear driving wheels, by means of a metal step-ladder.
4. Oddments : The Carmarthen & Cardigan Railway hired 2 engines of this type, which were all eventually sold to the SDR. The C&CR also had two side-tank 4-4-0 engines which were converted to saddle tanks after sale to the SDR. One 4-4-0ST was built for the Llynvi Valley Railway by Slaughter, Gruning & Co., sold to the SDR in 1868, and converted into a six-coupled machine in 1874. The Vale of Neath Railway operated 9 short-tanked locos, very like the 'Corsair/Comet' types, but with neater, straight-bottomed tanks.
After considering this ‘Broadsheet’ article in some detail, I moved away from the B&ER engines. There are potential difficulties in modelling the step-ladders, which have to clear the outside crank-pins while, at the same time, the valances of the splashers have to clear inside the coupling rods. Taken together, these present a major challenge to clearances in 4 mm scale. Apart from that significant factor, I also dislike the appearance of these engines with their cramped sheet-iron cabs (although these were later removed by the GWR)
On the other hand, I was drawn to the shapely curved sides of the bunker on some of the SDR engines, although some others had straight tops. So, after much deliberation, I decided to have a go at modelling ‘Aurora’ from the SDR ‘Short-tank’ group, precisely because it has so many interesting shapes to challenge my 3D-modelling ability!
The main dimensions, as listed in the RCTS booklet were :
- ‘Aurora’, built Jan 1852 by Longridge & Co, Bedlington
- wheelbase 17’ 9” (5’ + 5’ 1” + 7’ 8”)
- coupled wheels 5’ 9” dia
- bogie wheels 3’ 6” dia
- boiler barrel 10’ 6” x 4’ 5” dia
- firebox casing 5’ x 5’ 3”
- height 14’ 9”
- boiler pitch 6’ 8”
I used the same method that I described in my previous post to extrude the saddle tank from a drawing – this time a pencil sketch by F.J.Roche, reproduced in the ‘Broadsheet article. This drawing was useful for the front elevation but I feel the drawing in Mike Sharman’s compilation by the Oakwood Press is more dependable for the side elevation.
I imported the drawing into ‘Fusion 360’ as a ‘canvas’ and then extruded the length of the ‘short-tank’. I added the downward extensions in the central part of the tank by extruding rectangles and then used the ‘fillet’ tool to produce the rounded corners, as visible on the prototype photo above.
‘Aurora’ short-tank extrusion
I was especially pleased with the cut-outs since John Brewer, the author of the ‘Broadsheet’ article, commented that: “These earlier engines had short saddle tanks. leaving the firebox uncovered. Most had odd and asymmetrical cut-outs in the lower edges of the tanks, which might almost have been purposely designed to thwart the modeller.” Fortunately, the convenient features of 3D-modelling software came to my rescue!
Interestingly, the Longridge-built engines were taken by truck to Gloucester and tried out on the Cheltenham line, so they did fall loosely within the orbit of some of my other BG models, also based in Gloucester.
In his article, John Brewer wrote quite a lot about the difficulties to be faced by modellers of the time (1987) in attempting to create one of these engines. Reading his comments made me sincerely grateful for the advances in technology that have provided me with a 3D-printer! John also used an expression regarding these engines that I had to look up: he referred to their 'jolie-laide' character which so endeared these machines to the author. Now that I know what it means, I have to agree
I shall continue to construct my model along the lines described in my previous post – assembling the 3D-printed components around a brass tube representing the boiler. I hope to show more progress before too long.
Edited by MikeOxon