MikeOxon

Your model is a splendid example of historical research. The engraving by T.T.Bird is a reminder that newly-built railways looked more like motorways under construction than the verdant shrubberies that we see today. Those bucolic branch lines, so beloved of modellers, did not look anything like our perception of them today! In the case of Watford Tunnel, the landslip of 2016 led to the cutting being cleared of vegetation and then netted over, which restored something of the original 'bare' appearance - see https://www.can.ltd.uk/casestudies/watford-tunnel-devegetation-rockfall-netting Mike

and hydrogen combustion doesn't just produce water but NOx as well - just like other fuels.

I I think it may be down to Bird misreading Lane's annotations, which can be somewhat illegible. Another example I have found is the case of 'Evening Star', where Lane shows appropriate looking safety valve covers but with figures above them that seem to indicate a much larger diameter. Bird has drawn extremely fat covers, presumably based on his reading but, to me, they do not look 'right'. This is a complex case, because Lane's overall proportions appear 'stretched'. This seems to be a case where Lane's version really is a 'sketch' as many of his marked dimension do not tally with his drawings and his wheel are very small in proportion to the diemensions along the bottom of the sketch One day, I must study this engine in more detail 🙂 Mike

An interesting itinerary. I am unfamiliar with European rail routes and was slightly surprised to see you passed though Cologne (Koln) , which seems a bit of a detour on the way to Brussels but I assume it is where the high-speed lines run that matters. I used to travel on Eurostar quite a lot 20 years ago, when it seemed very modern but I suspect the covid years were not good for business and standards have dropped. Kings Cross was a building site for many years but appears to have emerged very well. Paddington too has had a good clean and shows up well against the older photos. I visit Reading frequently and it looks more and more like a small American city every time I visit - all shopping malls, carparks, and tower cranes! I'm sorry you had poor weather (and grimy windows) for the South Devon stretch because, in the right conditions, it still ranks as one of the great scenic railway journeys - you do have to make sure you get a seat on the seaward side to make the best of it, though. I have poor memories from my last Penzance trip, as it was made just as they were changing from HST sets to the Hitachi sets and no one seemed to have told the booking computer. We ended up in seats intended for disabled in a corner of the restaurant car, surrounded by kitchen trolleys and the like while, on the return journey, the system had failed altogether, with little food available and a very harassed lady trying to do the job of an entire team. At least we were spared a replacement bus service! Mike

Having wandered into South Devon territory with my atmospheric caper, I started to look at some of the steam engines used on that line. I realised that, although I have modelled several early passenger engines, including the Firefly class, I have not tackled any of the early goods engines. The Leo class 2-4-0 were built as goods engines, starting in 1841. It was soon realised, however, that they had insufficient adhesion weight, so all the engines were converted to carry saddle tanks. We are very fortunate that the young draftsman, E.T.Lane made sketches of ‘Leo’ both before and after conversion at Swindon Works in 1849. In fact, his two sketches were dated 13th September 1849 and 21st September 1849, which indicates how rapidly the conversion was carried out! Although these are only notebook sketches, I found that overlaying the two versions showed how similar they are and indicates that the sketches are actually rather accurate. Many of the key dimensions are written on the sketches, although the later one only shows those which changed as a result of conversion. Unusually, he also sketched end elevations for the tank engine. Sketches by E.T.Lane of Leo at Swindon in 1849 I decided that the saddle tank version was the one I would like to model and so I started to examine the available information in more detail. I should mention that there was a later ‘upgrade’ to many of these engines, when larger bunkers were fitted and that there are a few photos available of the larger-bunkered form. They must have been useful engines, because many of them survived until the great cull of Broad Gauge stock in the 1870s. I have mentioned before that caution is needed when taking dimension from drawings. In the present case, G.F. Bird made some more ‘finished-looking’ drawings, clearly based on Lane’s sketches, early in the 20th century. When I looked at one of these, reproduced in Mike Sharman’s book of Broad Gauge drawings, I thought that the tank tops looked very low, in comparison to the Lane sketches drawn from life. This could be seen clearly when I overlaid the Bird drawing over the Lane versions: Three drawings overlaid There are actually three drawings here – the first by Lane as a tender engine (Red), the second by Lane after conversion to a tank engine (Black), and the Bird drawing (Blue). Considering they are described as ‘sketches’, the Lane versions appear remarkably consistent in their scaling but the Bird drawing is very different in its portrayal of the tank. Fortunately, there is a good photo of ‘Aries’ (Leo-class) standing outside Faringdon shed, probably in the late 1860s by which time its bunker had been enlarged. Although it is not quite side-on, it is possible to compare the overall height of the tank with the diameter of the driving wheels (known to be 5 feet). The result looks to be much closer to the Lane sketches than to the much later Bird drawing (overlaid in red). Comparison of photo with Bird drawing To take the matter further, I decided to create a 3D model that I could then align with the photograph, to check how well the Lane dimensions agreed. I extruded the tank body, using ‘Fusion 360’, from one of the Lane end-elevation sketches and created the boiler as a cylinder, scaled from the prototype dimensions of 8’ 6” length by 3’ 6” diameter, as shown below: Extruding from drawings in Fusion 360 I copied the frames and buffer beams, by extruding in my usual way, and ‘borrowed’ a Haycock-style firebox from my earlier ‘Firefly’ model. Next, I assembled all these parts together, within ‘Fusion 360’, and then imported the photo of ‘Aries’ at Faringdon as a ‘canvas’. I could now rotate my basic 3D model until it appeared to be in a similar orientation to that shown in the photograph. Model and ‘Canvas’ in Fusion 360 I then overlaid the model and photograph, in order to compare the major dimensions. The result, shown below, confirms that the Lane sketches are an accurate representation of the height of the saddle tank. Overlay of my 3D model and photo of ‘Aries’ This is one of those rare occasions when one of the early engine designs survived long enough to appear in a good photograph. I have used 3D modelling as a research tool, to validate Lane’s sketch and to show that the much later Bird drawing is not accurate. Having got this far, I suppose can now proceed with a complete model of a Leo-class tank engine. According to Ian Pope & Paul Karau’s book “The Forest of Dean Branch, Vol.1”, the former station master at Cinderford recorded that the line was opened with a Leo-class engine ‘Virgo’, so I even have an excuse to include this engine in my ‘Bullo Pill’ collection . Mike

I should add that ink-jet printable vinyl takes acrylic paints very well - that's now my preferred medium. Mike

It's just possible that it could be one of the five early box wagons built by Braby and Carrs, which were supplied in 1838-39. These adopted Brunel’s original concept of placing the wheels outside the body of the vehicle. Part of one of these early wagons appears in a lithograph by J. C. Bourne of Pangbourne Station. Probably more likely to be a contractor's wagon, though. Old vehicles often seemed to end up on West Country broad gauge lines. Mike

Isn't it strange how, when you want lines to disappear they will not, yet you are experiencing the opposite. In my 3D prints I have tried all sorts of fine surface fillers etc but the layers are still visible. I usually resort to self-adhesive vinyl. You can buy ink-jet printable vinyl, which will absorb inks, so can be coloured as you require.

yes, but that big hole has to contain steam at high pressure, which means it has to be surrounded by a strong cast iron casting - that casting weighs a lot for each cylinder.

Have you consider wood? here are a number of laser cut wooden kits available. A supplier such as Cornwall Model Boats can provide various sheet materials beading, etc.. I have used their materials for building broad gauge track, for example. Mike.

I always find it depressing when I look at a close-up photo of a 4mm scale model. All sorts of 'faults' leap out from the photo, although they are unnoticeable in normal viewing. In my case, a major culprit is the layers in 3D printing - so obvious in a photo but not in reality. For slates, imagine it's been raining - they look much darker then! Mike

Sadly, the museum has closed and the building is now occupied by a fishing and boating club.

I may have exaggerated the framing a bit but it has to be visible on a 4mm scale model! The actual style is uncertain but one of Dawson’ paintings shows it, although not quite as in the dwg found by the BGS. extract from Dawson watercolour

Thank you Annie. I'm very pleased to see that Steve Flanders' model appears to be based on the same sources that I used. It would be interesting to see an operating layout that uses his system. I wonder how the 'magic incantations' for the piston carriage were written? If you look around, there are several videos about both the Indonesian and Brazilian atmospheric railways although few have a commentary in English. The idea of using a concrete box girder as the air duct is neat and I notice that the square plate attached to the carriage is described as a sail at one point.

Assembling the Parts In tackling the assembly of the components that I printed as described in Part 2 of this series, I was reminded of President Kennedy’s words “We choose to … do the other things, not because they are easy, but because they are hard“ I had realised that the assembly of the parts was not going to be easy but it turned out even trickier than I had expected. To re-cap, the parts I printed were as shown below: 3D printed Atmospheric Apparatus Components The tricky aspects arise from the need to align the four axle bearings with the appropriate axles. The locations of these axles are, in turn, determined by the placement of the axle boxes on the main carriage under-frame. My idea was to suspend the hangers, which carry the cylinder frame and the two cylinders, from a brass rod passing across the centre of the octagon. The inboard ends of the longitudinal frames have sockets to accept the ends of this brass road, thus holding together the entire upper part of the apparatus. I included holes in the octagon and hangers, plus sockets in the longitudinal frames, within the 3D models of these components and, rather to my surprise, they actually appeared as required from my basic 3D printer. A little opening out with a reamer was all that was required to enable a 1mm brass rod to pass through the octagon and the hangers, as I had intended. This stage of the assembly is shown below: Octagon, with Hangers suspended from Brass Rod In this photo above, the octagon is actually upside down, as I soon realised, but it does show the method of assembly quite clearly. I used superglue to attach the lower ends of the hangers to the piston frame, then clamped these parts together to allow the glue to harden. Next, it was time to press the longitudinal frames onto the ends of the brass rod and align the whole assembly with the axles of the carriage wheels. At this point, I realised that the octagon was upside down and also that the brass road had to be removed to allow the central axle to pass through the bearings on the octagon – now turned downwards. Getting everything to fit together proved to be something of a trial! [understatement] The parts are small and it was difficult to hold every thing still, in order to set up the correct alignments. Fortunately, the brass rod was quite a firm fit into the ends of the longitudinal frames, so this helped me to wiggle everything into place, without it all falling apart. I think some more thought about this part of the assembly might result in a better method but we are where we are! After a certain amount of cursing and swearing, the assembly looked like this: Atmospheric apparatus attached to Carriage Chassis It was a great relief when I found that the sloping longitudinal frames did not clash with the lateral parts of the carriage frame, although it was close! My 3D model proved itself to be accurate! When in the operating position, the piston carriage hangs below the level of the running rails but, in my model, it is hinged like the prototype, so it can be swung to one side to allow this vehicle to run on normal track. All that remained was to attach the two pistons, connected by a brass piston rod to the piston carriage and the model was complete – hurrah! My 4mm scale 3D-printed model Piston Carriage On the evidence of the contemporary paintings by William Dawson, it seems most probable that the carriages were painted brown overall, so I have adopted this colour for my model. After fettling, painting, and general ‘tidying up’ of the model, I posed it on my short length of broad gauge track. The roof is covered in self-adhesive vinyl. I used a leather punch to create holes in the vinyl for the oil lamp housings. The windows are glazed with overhead transparency sheet. The piston for the atmospheric apparatus can be seen below the front buffer beam of the carriage. My 4mm scale model of SDR Piston Carriage The Atmospheric Train in Operation To add a sense of realism to the scene, I placed a few of my models against a back-scene representing the red sandstone cliffs at Dawlish Warren: Diorama showing some of my Broad Gauge models I think it might be useful to add a few notes on how the trains were operated and how the pistons under the carriage were inserted into the propulsion pipe. The first point is that the system was designed for single-line working only. Because the flap valve was hinged to one side of the slot along the top of the pipe, it had to be raised by the apparatus below the carriage from the side opposite to the hinge. Research by the BGS strongly suggests that the hinge ran along the ‘seaward’ side of this coastal railway, from which it follows that the lifting apparatus must work from the landward side. Surprisingly, the protective metal covers, shown in Samuda’s Patent illustrations, were not fitted, despite the obvious detrimental effect on the leather arising from the seaside environment. Patent Illustration showing hinged leather seal Because of this ‘handed-ness’ the carriage always had to work in one orientation and could not be turned. That is why there had to be two pistons and driving compartments at both ends. Brakes were only fitted to the wheels on the landward side, so the drivers position was towards that side, where the brake operating levers were situated. The propulsion pipes were laid in 3 mile lengths, each length attached to a pumping station. Flap valves at the ends of the pipe were opened in response to a trigger device, operated as a train approached the end of one of the pipes. Once the pistons had entered the evacuated pipe, the driver had no means of regulating the speed of the train other than by applying the brake. The propulsion pipes stopped short of stations and the train ‘free-wheeled’, in the manner of a slip coach, after leaving the pipe until stopped, hopefully at the station platform, by the driver. Under- and over-runs were apparently not infrequent. At that time, manhandling or horse-shunting of railway vehicles were not unusual and these were, in general, the only methods available, if the train had to be moved when ‘off’ the pipe. The exception was for starting a train from a station. An auxiliary pipe was laid alongside the track ahead of each station. This pipe contained a piston attached to a length of rope that could be hooked to the front of the piston-carriage. The rope started the train into motion until the pistons entered the main propulsion pipe, when the driver released the staring rope. The flying end of the rope was a potential hazard to any gangers that might be near the line at the time! Before the train could start, the pumping engine for the appropriate section of pipe had to be operated. This was done according to the timetable so, if a train was late, the pumps had to be run for much longer than was strictly necessary, which increased the costs of running the system. Curiously, although the electric telegraph was installed along the line, it was never used to signal when the pumps were needed! Whenever the piston carriage had to be taken off the main line, its atmospheric apparatus had to be raised, in order to clear any pointwork and crossings. This was achieved by use of a winding handle fitted into a socket on the seaward side of the carriage. All these factors were clearly inconvenient, when compared with the flexibility of steam locomotive working. For any one who wishes to learn more about this railway, I can recommend the book ‘Brunel’s Atmospheric Railway’ which, apart from containing the set of 25 contemporary watercolour illustrations by William Dawson (1790-1877), provides extensive text and drawings, edited and produced by Paul Garnsworthy of the Broad Gauge Society (BGS). A new edition has recently been printed. Addendum Robert Stephenson carried out a technical review of the Kingstown & Dalkey atmospheric railway in Ireland in 1844. Kingstown & Dalkey atmospheric railway His conclusions were: 1st That the atmospheric system is not an economical mode of transmitting power, and inferior in this respect both to locomotive engines and stationary engines with ropes. 2nd That it is not calculated practically to acquire and maintain higher velocities than are comprised in the present working of locomotive engines. 3rd That it would not in the majority of instances produce economy in the original construction of railways, and in many would most materially augment their cost. 4th That on some short railways, where the traffic is large, admitting of trains of moderate weight, but requiring high velocities and frequent departures, and where the face of the country is such as to preclude the use of gradients suitable for locomotive engines, the atmospheric system would prove the most eligible. 5th That on short lines of railway, say four or five miles in length, in the vicinity of large towns, where frequent and rapid communication is required between the termini alone, the atmospheric system might be advantageously applied. 6th That on short lines, such as the Blackwall Railway, where the traffic is chiefly derived from intermediate points, requiring frequent stoppages between the termini, the atmospheric system is inapplicable ; being much inferior to the plan of disconnecting the carriages from a rope, for the accommodation of the intermediate traffic. 7th. That on long lines of railway, the requisites of a large traffic cannot be attained by so inflexible a system as the atmospheric, in which the efficient operation of the whole depends so completely upon the perfect performance of each individual section of the machinery. I remain, Gentlemen, Your most obedient servant, ROBT. STEPHENSON. Stephenson’s assessment, especially his 5th point, is being re-applied with modern technology in both Indonesia and Brazil. See https://www.youtube.com/watch?v=GM2Zxn7ybNQ Mike

According to Alan Peck's "The GW at Swindon Works", Dean wrote to the electrical engineer, Crompton, in 1892 that he had been instructed by the Chairman to discuss the subject of electrical haulage through the Severn tunnel. It seems that Dean showed no enthusiasm for the idea - perhaps he saw it as another potential 'atmospheric railway' type of disaster - and the correspondence fizzled out. I explored what might have happened in the Imaginary Locomotives thread: https://www.rmweb.co.uk/topic/14790-imaginary-locomotives/?do=findComment&comment=1358729 Mike

I'm writing Part 3 at present and will include something about these 'features'. In those early days of railways, manhandling and horse-shunting were commonplace activities at stations and yards. Lack of operational flexibility was a major reason for the 'atmospheric's' failure. When the continuous leather valve failed and needed replacement, the Directors decided to cut their losses and opted for steam locomotives instead.

Thank you very much Dave. Actually, there was no 'return track' - another great limitation of the system! - it was just a single line. The offset in the hangers meant that the carriage could not be turned. Manoeuvring the carriage at stations was another nightmare! I'll write something about it in my next post. The good news is that I have managed to assemble the parts but I shall aim to complete the whole thing before I post again. I'm so pleased you enjoyed it, Annie. The research was really done by BGS members and I interpreted their work for the model. I felt that the information the BGS unearthed has been unjustly neglected, so people are still making models based on that illustration by Robert Barnard Way - there was one in Railway Modeller, July 2023.. The model making was a bit 'Brunellian' - great in principle but a pig to actually realise!!! I think I'm on top of it at the moment - the next post will tell! Mike

Introduction In Part 1 of this series, I described my model of the piston-carriage for the South Devon (SDR) atmospheric railway, based on drawings by Paul Garnsworthy in the Broad Gauge Society (BGS) Journal ‘Broadsheet’Nos 44 and 46. It’s been great to receive so many positive comments – clearly some of my viewers like reading about ‘forgotten’ corners of railway history. They spurred me into getting on with the next phase. Thank you! The carriage body was relatively straightforward, being similar to other broad gauge carriages that I have already modelled. I felt, however, that I should attempt to understand the workings of the system and I find that the best way of doing this is to build a model. There are several drawings in the Patent Application by Clegg and Samuda but these were only intended to illustrate their ideas and contain features that were never used in practical applications of their idea. It was pointed out to me recently by a fellow member on this site @drduncan that the principle is the same as that used in the steam catapults on aircraft carriers in the Navy. It was in that context that I found some very clear drawings that illustrate the principle very well: Slotted Pipe for Steam Catapult In the SDR application, the sealing flap was made from leather strips that were hinged along one side of the slot. This meant that instead of being lifted bodily, as in the illustration above, it had to be raised at an angle, from the side opposite the hinges. As a result of research by members of the BGS, negatives of drawings of the original SDR piston carriage were found in Bristol Museum and re-drawn by Paul Garnsworthy for the BGS Journal ‘Broadsheet’. This was no mean task, as the originals were not only very faded but consisted of a series of partial or split views, typical of the period. There are various plan and elevation views of the mechanism, which I found needed careful study to determine how the various components were arranged (N.B. I’m no expert in reading engineering drawings!) The description in the two ‘Broadsheet’ articles helped to shed light on the various complexities. The following is based on those articles How it Worked The chassis framing beneath the carriage was quite conventional for the period, except for the central bay, where a wide space was left for the atmospheric apparatus. This apparatus was carried by bearings on the wheel axles, with two bearings on the central axle and one each on the outer axles, The atmospheric apparatus. had its own substantial frame composed of iron plates, In the centre these formed an octagon, carrying the two bearings on the middle axle. From this octagon, longitudinal plates extended to single bearings located centrally on the outer axles. Two hangers, pivoted from the octagon, suspended a longitudinal plate, which hung below the carriage and passed through the slot in the top of the main propulsion pipe, set between the running rails. These hangers were angled to raise the leather sealing flaps on the opposite side from their hinges, running along one side of the slot. Once the hangers were inside the propulsion pipe, they were attached to a pair of 11 foot long piston frames. Between these frames there were five rollers, which functioned to raise the hinged sealing flap, fitted along the upper slot of the propulsion pipe, and let it down again, once the plate connecting the pistons to the carriage had passed. There were two additional rollers mounted on the main assembly, above the pipe, to ensure that the flap valve was pressed down firmly after the carriage had passed. Piston rods extended from each end of the piston frames, inside the propulsion pipe, to the pistons themselves, which were located towards each end of the carriage. The two pistons allowed the carriage to be operated in either direction, so that it did not need to be turned at the end of a journey. In operation, the propulsion pipe, set between the running rails ahead of the carriage, was evacuated by stationary steam engines. Atmospheric pressure acting on the piston from the back of the carriage then pushed the carriage and its train forwards. Behind the leading piston, the rollers on the piston frame raised the sealing flap so that the blade connecting the carriage to the pistons could pass through and then, towards the back of the piston carriage, a top roller re-made the seal, so that the pipe could be evacuated again for the next train. Creating my Model Once I had worked out how all the gubbins were supposed to work, I could start to create a model. The drawings show lots of additional rods and levers, not all of which are understood, so I concentrated on the major elements of the system. As usual, I started by importing drawings as ‘canvases’ in ‘Fusion 360’ and extruded the various components by tracing over these. Although the following description may seem straightforward, the actual design and fitting together of the various components involved a great deal of trial and error! I started with the main carriage frame, which provides an overall orientation reference and defined the mounting points for the wheels and axles. I added the springs and axleboxes by the same methods as for my earlier designs. 3D sketch of carriage underframe and wheels With these key reference points in place, I could then start to create the atmospheric equipment, described above, around them. As usual, I extruded these parts from a drawing. I placed axle bearings on the central octagonal plates and on the longitudinal plates, in their proper locations over the three axles. The frame (red) carrying the atmospheric equipment underneath the carriage The next major component to create was the piston frame and pistons, which ran inside the propulsion pipe when the train was operating. This component is made up of several parts: two frames, the piston rods, the pistons themselves, rollers, and the hangers which couple this component to the octagon and thence to the train.. The piston assembly that runs inside the propulsion pipe In the prototype, the hangers were connected to the octagon on pivots. These allowed the complete piston assembly to be raised clear of the track, in case the piston-carriage had to be attached to a normal train or simply to negotiate points and crossings (which were another problem for the atmospheric system) Having created the various parts separately by tracing over the drawings, I then used the ‘move’ tools in ‘Fusion 360’ to bring them together into the correct alignment. At this stage, it became apparent that several minor adjustments to dimensions were necessary, to ensure that all the parts fitted together neatly in the correct orientations. I made two screen shots of the assembly: first with the pistons in the operating position and then hinged to one side by 45°, in order to clear normal trackwork. The Atmospheric Equipment in raised and operating positions I should re-emphasise that these 3-D sketches are simplified, to illustrate the basic operating principles of the atmospheric equipment. The raising of the piston assembly was achieved by pinion gears and shafts, which could be operated by a removable handle, rather like the starting handle on an old-fashioned car. Other control rods could adjust the pressure applied by the flap-closing rollers, as appropriate for the direction of travel. There may also have been linkages to open relief valves in the pistons since, apart from applying the brake, there was no provision for regulating the speed of the train. This last factor once caused a major panic for the crew of a train on the Kingstown and Dalkey Railway, when they forgot to attach the piston-carriage to its train before starting. It is said that the carriage, operating as a ‘light engine’, reached a speed of 80 mph but, fortunately, was stopped before there was a disaster at the top of the incline! In addition to the atmospheric gear, a braking system, controlled by handles in both the driving positions at the ends of the carriage, was fitted to operate on one side only. Printing the Model It was immediately apparent, from the small sizes of some of the components, that a working model in 4mm scale could not be created solely by 3D printing. In particular the various rollers and the piston rods would need metal components. Unless, however, I was also prepared to build some miniature slotted pipe and flexible valve strips, the model would not be operational anyway so, simply as a demonstration model, I felt that a realistic ‘impression’ could be obtained by taking a few ‘short cuts’. These applied mainly to the piston assembly that runs inside the propulsion pipe. I decided to embed the rollers within a solid piston carriage and run a brass wire longitudinally to connect this part to the two pistons. This proved more awkward than it sounds, as I also wanted a flat face, to lay on the printer bed but, after much trial and error, I found a solution that involved splitting the piston carriage into three printable pieces. I similarly embedded the two flap-closing rollers into the upper frame and fitted another brass wire across the length of the octagon, to carry the pivoting hangers. Now, at last, it was time to think about making some trial prints. Once I had a collection of what I considered to be ‘printable’ parts, I passed the drawings to the ‘Cura’ slicing program. At this stage, a few more problems emerged. I still don’t know how it happened but some parts were inclined at very small angles, such as 0.3 degrees. I do know that I have never experienced this problem before so, perhaps, there has been some change to the ‘Fusion 360’ software that allowed this to happen. Fortunately, it could be corrected by simple rotations in ‘Cura’, until the components lay flat on the printer bed. Another problem emerged because I had failed to note that the body of the piston carriage was unusually narrow for a broad gauge vehicle, at only 8’ 4” wide. I should have been warned by the comment in the ‘Broadsheet’ article that “Nevertheless, [the frames] came perilously close to the wheels (7’ 7 ½ ” over wheels / 7’ 8½ ” between solebar flanges”. I had left insufficient clearance between the body sides in my original design to fit around BGS wheelsets, so I have had to widen and re-print the carriage body. I knew that I was taking risks with some of the ‘printable’ parts I created but, in fact, my old Geeetech printer coped admirably with some rather small dimensions and awkward shapes. The first step was to print the main chassis members and fit the wheelsets. This went well, as shown below: My 3D-printed underframe and BGS Wheelsets The next step was printing the octagon and longitudinal members that carry the atmospheric apparatus. I designed these to be linked together by a brass rod passing across the width of the octagon, which I intend to use for suspending the lower parts of the equipment. Since these are all small parts, I added the piston frames to make a ‘set’ of parts for printing together. The complete set printed in just 19 minutes. As mentioned above, I simplified the design of these parts so that they all had flat faces that could lie on the printer bed. The ‘rollers’ are not movable but printed as integral parts of the frames. After printing, the complete set appeared as below: My 3D-printed Atmospheric frame parts I printed the remaining small parts as a separate group, since they all involved more complex shapes, which I anticipated might prove difficult. To minimise the possibility of these parts toppling over while printing, I selected the option in ‘Cura’ to surround each part with a ‘brim’. I prefer to avoid support structures whenever possible, as they can be difficult to remove cleanly – even very thin layers of printed PLA can be remarkably tough! In fact, even the very small ‘hangers’ came out better than I had expected, though the brim was not easy to remove from these. I find the only successful tool for this job is a finger-nail. I show these parts still in place on the printer bed - note that the cylinders are only 11 mm long. Note also the holes in the hangers, to allow them to be suspended from the octagon. The thin strips attached to the hangers are to allow these very small parts to be glued to the piston frame (the one with 5 rollers) shown in the previous illustration. My 3D-printed cylinders and hangers on Printer Bed As I mentioned above, I had to re-print the carriage body a little wider, in order for it to fit over the wheels, after which the whole kit and caboodle looked as below: All parts for my model Atmospheric Piston Carriage As with many jobs, it all looks quite simple now it’s done. Perhaps it’s down to my increasing age but this one cost me more “tears and sweat” than anything else I’ve made since I started trying my hand at 3D printing. I shall pause here for a stiff drink and then tackle the job of assembling all those small pieces, which will disappear out of sight underneath the carriage! I’m still thinking about the colour of the carriage. I think it looks nice and rather ‘rustic’ in brown. Mike Feature Photo - William Dawson, "From the Station in St Thomas to the Alphington Meadows", detail

An excellent example of pictures being worth thousands of words. I've really enjoyed browsing this post 😃 Mike

Thank you for such an enthusiastic response, Crompton. I have though about propulsion, possibly by using a magnet to connect the car to the piston, but my current problem is to create a model of the apparatus under the car! The did run goods trains and the last one to run was in fact a goods train to Exeter. The late Eddy Brown, who contributed so much research to the BGS, made a drawing of a goods train, which can be seen in 'Broadsheet' no.44 (Autumn 2000). Brunel certainly had great powers of persuasion. He frequently managed to convince otherwise staid bankers to support his idealistic schemes. He always seemed to have a blind spot concerning railway engines, though, since his specifications for steam locomotives were disastrous when implemented.

I like to try and correct 'fake news' 😄 I agrrr that it must have been an exciting day for the BGS. I suspect there are quite a few followers of the 19th century GWR who hope that some drawings of the semi-mythical 4-2-4T No.9 will eventually turn up somewhere. Mike

I've been on a steep learning curve and intend to write about it in Part 2. The truth is that it didn't work well in practice and not just because the appropriate materials weren't available. There were just so many shortcomings, when it came to adapting the idea to railway operations. No points, no cross-overs, and very little control for the 'driver' of the train.

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"

as Beerbohm put it - " that antique station, which, familiar to them and insignificant, does yet whisper to the tourist the last enchantments of the Middle Age."