Introduction

 

Having worked my way back to the very beginnings of the GWR, it’s been hard to think of where to go next. I’ve enjoyed exploring those odd-ball engines that Brunel ordered for his new concept of a railway, even though they proved to be disastrously undersized. Nevertheless, several of them had quite long lives as branch-line engines.

 

I do enjoy ‘bringing to life’ forgotten areas of railway history and, for the broad gauge, the ultimate in odd-ball ideas was, perhaps, the atmospheric railway that Brunel decided to recommend for the South Devon Railway.

 

Atmospheric Railway showing Pipe and Pumping Station at Dawlish
by Nicholas Condy (1793-1857)

 

The basic idea was to move things along a pipe by evacuating air from the pipe ahead of the vehicle, so that atmospheric pressure would push from behind. This concept found some long-lived applications in shops and other businesses, where it was used to carry paperwork and cash in small canisters around a building.

 

In 1840, two engineers, Clegg and Samuda, laid out a half-mile long track at Wormwood Scrubs, where railway carriages were drawn along by a piston, placed within an evacuated iron pipe set between the running rails. Several engineers were invited to view the demonstration and, whereas Stephenson dismissed it as a ‘great humbug’, Brunel was captivated and went on to propose it for use on the South Devon Railway.

 

He wasn’t alone and the idea was adopted by a few other railways, including the Nanterre to St Germain railway in France. The first to be built, in 1843, was the Kingstown & Dalkey Railway, on the outskirts of Dublin. It was only one and three-quarter miles long and the atmospheric system was used to take trains up an incline, from which they returned by gravity. A trial was also made on a 5-mile stretch of the London, Croydon & Epsom Railway, authorized in 1844 and opened in January 1846. Many problems were encountered and in May 1847 the whole line was converted to locomotive operation.

 

Typically, Brunel’s plans were more grandiose. On Brunel’s recommendation, the South Devon Railway laid fifteen miles of single track from Exeter St David’s to Teignmouth, later extended by a further five miles to Newton Abbot. The intention was to apply the atmospheric system all the way to Plymouth, so Brunel allowed some unusually steep gradients along his surveyed route, on the assumption that they would be operated by atmospheric traction ... but matters never got that far!

 

Atmospheric operation of the line was very short-lived: public operation began on 13th September 1847 and within the year it was all over!.  The last atmospheric train arrived at Exeter during the night of 9/10 September 1848. This isn’t the place to go into all the reasons for such a catastrophic failure – suffice to say that the multiple reasons were both technical and economic in nature.

 

Misconceptions

 

So why do I want to make a model? My main reason is that there are serious misconceptions about what the railway actually looked like. A lot of credence was given to images based on Clegg and Samuda’s Patent Application, which actually bear very little resemblance to what was actually built. The illustrations were only intended to indicate the principles of operation, as shown below.

 

Schematic diagram from Samuda and Clegg’s Patent on atmospheric railway. 

 

Unfortunately, a commercial artist and writer, Robert Barnard Way, active from 1930 to 1958 created an atmospheric railway scene based on Nicholas Condy's painting of Dawlish (above), with the addition of a train headed by a simple flat car, as shown in the Patent diagram. There are now a great many copies of this image in circulation, so I shall avoid perpetrating this error.

 

A true description of the piston carriage used on the SDR came to light during a meeting of the Broad Gauge Society (BGS), held at Bristol Museum in 1993. There was an opportunity while they were there to browse through the Woodfin Collection, where some BGS members were astonished to discover a real bombshell. Negatives 14471, 14894-14896 and 16141-16150 actually recorded drawings of one of the elusive South Devon Railway piston carriages. Paul Garnsworthy of the BGS created new drawings from the rather faded images and published a pair of articles, including his drawings, in the BGS Journal ‘Broadsheet’ issues 44 and 46. (available to BGS members in digital format)

 

In order to set the record straight, I decided to create a model based on these drawings, using my usual methods of extruding from drawings by means of ‘Fusion 360’ software.

 

Creating my Model

 

The first step was to import the drawings from ‘Broadsheet’ as a ‘canvas’ in ‘Fusion 360’. After scaling to 4mm/foot, I copied the main outlines of the sides and ends, before adding details of doors, windows, and panelling. All these were created by means of the ‘rectangle’ and ‘3-point arc’ drawing tools

 

My sketches of the carriage side overlaid on the ‘canvas’

 

I then used the ‘push-pull’ tool to raise the mouldings above the main extrusion of the side, to create a solid model.

 

The ends of the carriage were created in exactly the same way from the appropriate drawings. The sides and ends were all created as separate ‘bodies’ within ‘Fusion 360’.

 

The floor was created as a simple rectangle and the roof was similar except for an arc profile. I added two oil lamp housings to the roof, placed to be shared between the 2nd and 3rd class compartments, This was a common practice in the early days, when any sort of lighting was considered a ‘luxury’!

 

Once all the parts were extruded, I created a rendered image of the complete assembly in ‘Fusion 360’. The colour of these carriages is unknown. Brown was the standard colour used on both the GWR and the SDR but there is evidence that at least some 2nd class SDR carriages were painted green. I decided to use green, simply to provide a contrast to my usual stock.

 

Accommodation in the prototype comprised two 2nd class compartments towards each end and a central area for 3rd class passengers. The piston carriage was designed to be bi-directional and was not turned at the end of a journey. Because much of the SDR line ran along the coast, the two sides can be referred to as the ‘seaward’ and ‘landward’ sides. Brakes were only fitted on the landward side so the driving position was offset to this side at both ends of the carriage.

 

my rendered piston-carriage body created in Fusion 360

 

For printing, I divided the components into just four parts – 2 sides, roof, and a floor combined with ends and partitions.

 

The four components ready for ‘slicing’ and printing.

 

This division into components allowed me to lay the sides flat on the printer bad, so that there was no need to provide additional support to the window openings. The roof is flat on the underside and the other parts are printed from the floor upwards. I could separate the ends, if this proved necessary to achieve clear window openings but, in practice, I have found that my printer copes well with small simple rectangular openings like these.

 

Printing my Model

 

The printing all went smoothly, including the floor and partitions, where I had hoped that the window openings would print reasonably cleanly without additional supports. There is a little stringing visible (I used the Geeetech printer) but nothing to cause any difficulty.

 

Floor and Partitions on Geeetech E-180 printer bed

 

I then printed the two sides and the roof, which included two oil-lamp housings, shared between adjacent compartments. I continue to be amazed by what my printer can achieve. In this case, I could see light through the small holes in the lamp covers that I had included in the 3D model,.

 

My 3D-printed Piston Carriage Body with oil-lamp housings

 

Of course, this was just a straight-forward carriage design. I now have to tackle the underframe, with its attachments to the atmospheric pistons. On the prototype, these were pivoted such that they could be raised if the carriage had to pass over crossings in ‘ordinary’ track.

 

I intend to represent them in the raised position or, if I can manage to do so, I may even make them hinged! I anticipate that creating them, such that they can be 3D-printed, will be a challenge and I suspect that some ‘hybrid’ construction methods will be necessary.

 

Mike

 

Feature Photo: watercolour by William Dawson (1790-1877) - "view of Newton station, via Brunel's Atmospheric Railway"