Continuing the story, time to look under some sixwheelers, first off a pair of my old ones, scratchbuilt for an Irish Line. Contrasting them with a sixcoupled loco, the wheelbase for a loco is around 4.3”/108mm, and for a coach is 5.8”/ 148mm. Generally I build my locos with an uncompensated chassis for the drivers, just some float allowed for the carrying wheels. As long as the driver flanges are all touching down to start, they can run quite well on my track. With a coach the extra length does allow track irregularity to become more of a problem if the wheels are mounted rigidly. If the centre wheels sit on a hump, the leading wheels can rise off the rails, and then it’s only how deep the flanges are that can save the situation, which is where coarse scale modellers score over finescale. Because of this I like to have the centre pair capable of deflecting, with some springing. Then in plan view having the outer wheel sets sitting on a curve, the centre pair have to have plenty of sideways displacement allowed for, much more than a loco needs.
These two underframes meet these needs in two different ways. The one chassis, at the bottom, has the outer wheel sets mounted using Slaters components, one fixed to the coach floor, the other on a rocking mounting, common to a lot of their wagons. Then the centre set has inside bearings, with plenty of side movement, and springy brass strips to keep the wheels in contact with the rails.
The other chassis has a fixed wheelset mounting at one end, and the other two wheel sets mounted as a “bogie”, allowing plenty of movement. Both these work well, I think I prefer the non bogie one of the two, just because it’s easier to put the coach on the rails when the wheelsets are hidden behind footboards.
George Armstrong's Masterpiece
George Armstrong's Masterpiece
In another thread, I explored some of the earliest standard-gauge locomotive to run on the Great Western Railway. The first of these were from the two Shrewsbury railways, which were absorbed by the GWR in 1854. Not only did the GWR acquire a very miscellaneous collection of locomotives from these railways but they also gained a locomotive engineer by the name of Joseph Armstrong.
Joseph Armstrong soon became responsible for all standard-gauge locomotives running north of Oxford, but he had little opportunity to design and build his own engines until the resignation of Daniel Gooch, ten years later in 1864. Then Joseph moved to Swindon, to take on the immense burden of transforming the GWR from a broad-gauge to a standard-gauge railway. When he moved, however, he left his younger brother, George Armstrong, in charge at Wolverhampton, with a high degree of independence, which included retaining the blue-green livery, originally used by the OW&WR.
Thus, it was George who took on the task of renewing the locomotive stock in the Northern Division of the GWR. Initially, his designs followed the ideas of his brother very closely, but then he designed a small tank engine with an 0-4-2 wheel arrangement, which was to achieve a fame and longevity out of all proportion to its size. If I mention that the first of these locomotives, built in 1868, was No.1040, it will probably ring few bells in anyone's mind but, if I mention that the first sixty were re-numbered in 1870 into a sequence starting at No.517, then these will be recognised as some of the true 'greats' in locomotive history - a greatness based not on 'flashy' deeds but on sheer competence and overall utility.
For the modeller, the '517-class' presents both opportunities and problems. Over the years, the class received so many modifications that it would be possible to build a diverse collection of models based solely on this class! On the other hand, there were so many re-builds that applying a running number to a model is fraught with dangers, since the result could bear very little resemblance to any of the many incarnation of its prototype.
A few years ago, I made a rather simplistic conversion of a K's 'autotank' into a loose representation of a '517-class' locomotive. The original model had a Belpaire-type firebox and I wanted to include inside trailing-wheel bearings, so I hit on a photo of No.835, which showed both these features on the same engine. More recently, however, I've started to look at how the prototype engines were developed over the years. Although, there is much detailed information in the RCTS Part Six of 'The Locomotives of the GWR', it is quite difficult to extract the information most relevant to modellers, when it is spread over 12 pages!
For my own interest and, hopefully, of some use to others, I have made the following summary, starting with the original forms of the various stages of construction. I have concentrated on visually obvious changes, such as wheelbase and tanks, rather then on the lot numbers. I based my coloured illustrations of the different stages on original photographs. EDIT Since reading 'Great Western Way' more carefully, I have changed the splasher fronts on Wolverhampton engines to green, rather than brown, as originally posted.
A few things remained constant throughout : the mainframes, the layout of cylinders and motion, the principal boiler dimensions, and the coupled wheelbase : 7' 4" throughout. The wheel diameters were 5' 0" and 3' 6" for the coupled and trailing wheels respectively, although both these dimensions grew by 2" over the years, as a result of fitting thicker tyres.
First Group - built between 1868 and 1870
The first 60 engines were saddle tanks, except for the final six, which had side tanks from new. They were numbered from 1040 to 1087 and from 1100 to 1111 until July 1870, when they became Nos. 517 to 576. (I'll use the later numbers in the following descriptions of the changes)
Even within this first group, the overall wheelbase started to increase; first from 13' 7" (Nos. 517 - 522), to 13' 8" (Nos. 523 - 552), and then a jump to 14' 8" (Nos. 553 - 576, which includes the first engines to be built with side tanks : Nos. 571 - 576)
No.517 in original form, with short 13' 7" wheelbase
shown in Wolverhampton livery
No.556 in original form, with longer 14' 8" wheelbase
also in Wolverhampton livery
Second Group - built between 1873 and 1885
This was the largest group, comprising 90 engines, mostly turned out in batches of a dozen at a stretch. Numbers lay in various ranges: 826 - 849 (24 engines), 1154 - 1165 (12), 202 - 205 and 215 - 222 (12), 1421 - 1444 (24), and 1465 - 1482 (18). All these engines had side tanks and a common overall wheelbase of 15 feet (7' 4" + 7' 8") Other developments in boiler and tank details occurred during the build period.
No.1164 with side tanks and 15' wheelbase
shown in Wolverhampton livery
Third Group - built 1885
This was a small group of six engines, Nos. 1483 - 1488, which were the first to be built with outside axle-boxes to the trailing wheels, together with a further increase in the overall wheelbase to 15' 6".
No.1487 as built, with outside bearings and 15' 6" wheelbase
shown in Wolverhampton livery
Set out like that, it all looks fairly simple but then the modifications and re-builds began, with all the improvements made in the later groups being applied to earlier engines.
The first step was the conversion of saddle tanks to side tanks, which was (mostly) accompanied by increasing the wheelbase to 15 feet. (Occasionally the two 'operations' were staggered). This applied to almost all of the first group between 1876 and 1886, with most being converted at Wolverhampton, although four were done at Swindon. I guess that the Swindon conversion may have resulted in a livery change to the Swindon style - they certainly acquired polished brass dome covers.
No.551 as re-built at Swindon, with outside bearings and 15' 6" wheelbase
shown in Swindon livery
By the end of the 19th century, there were only two wheelbases, 15 feet and 15' 6", with all the latter having outside bearings for the trailing wheels. Reconstruction continued at Swindon until 1915, providing new frames and the longer wheelbase, with outside bearings. Meanwhile, at Wolverhampton, lots of changes were also being made, to improve bunker capacity, for example. This involved lengthening the frames by 6 inches, without any change to wheelbase or bearings. The most noticeable differences, below the footplate, between Swindon and Wolverhampton engines were in the depth of the valances and the shape of the footsteps.
Above the footplate, cabs and bunker designs were constantly evolving. The variations are really too complex for a brief summary here so, I fear, one is forced to look at information for each individual locomotive - much of which can be found by carefully scouring the pages of the RCTS Part Six of 'The Locomotives of the GWR'
In the case of my own model of No.835, I now know that this started out in December 1873 as a side tank with 15' wheelbase. It was re-boilered in 1894, again in 1910, and then received a Belpaire boiler in 1916. For some reason, it retained its original inside bearings and wheelbase throughout, being finally withdrawn in 1935.
No.835 after receiving a Belpaire firebox in 1916
Shown with black frames (post 1906)
So, my model is quite wrong in combining Indian Red frames with a Belpaire boiler and it certainly should not have wing plates on the smokebox. I still enjoy it as a model, though, and perhaps one day, I shall be inspired to build a more authentic version ....... but, which to choose?