Someone once said that “I assume ...” is one of the most dangerous statements that can be made.
In my previous post , I described my study of the valve-gear of early locomotives, starting from the Stephenson ‘Patent’ design, which set the template for much of the first half of the 19th century. I managed to find detailed drawings of the valve gear on Gooch’s Goods locomotives and I assumed that the arrangement in the Waverley class would have been similar – after all, the boilers were of the same dimensions and both types were built in the same period.
Just as I had made a sketch of my assumed layout, I saw a drawing of the Waverley class locomotive in Gooch’s own notebooks (now in the National Railway Museum) This drawing, together with those of many other early Broad Gauge locomotives can be found on the web at https://www.gettyimages.co.uk/search/more-like-this/90744559?family=editorial&sort=best#license
When I looked at this Waverley drawing, I noticed that it showed the upper slide-bars, with a fitting, apparently mounted on them, that looked like a trunnion, to carry the cross-shaft for operating the reversing gear, above the rest of the motion.
If my reading of this drawing was correct, it meant that the valve gear was not the same as that on the Goods engines, where the shaft lay below the motion.
Before making any more assumptions, I decide to look for corroborating evidence. One again, fellow members of the Broad Gauge Society came to my aid and provided me with a clearer copy of the NRM 4742 drawing, which I showed in the previous post
Although this is a very ‘busy’ drawing, with a confusing array of components all overlaid on top of one another, I was able to pick out some of the key features of the valve-gear from all the surrounding details. My own interpretation of this area of the drawing is shown below.
Since this NRM drawing is in good agreement with the other drawing from the Gooch notebook, I am now reasonably confident that, taken together, they represent accurately the layout of the valve gear on the Waverley-class locomotives. There are other features on these drawings that remain unclear to me but I am satisfied that I have found answers to my original queries.
So, now I had to decide what to represent in my model ...
For convenience in assembly of my model, I decided to fit my simplified representation of the ‘motion’ to the chassis, thus allowing the body to be separated easily. This meant some re-arrangement of the back of the smokebox (which enclosed the cylinders in the prototype) from the way it has been implemented in the BGS kit for the Gooch Goods (on which my model is based).
I decided to fit my non-working gear into a ‘module’, which could be placed between the sandwich frames, extending forwards from the motion plate to the lower part of the smokebox, surrounding the cylinders. I took material from the nickel-silver fret of motion parts, included in the BGS kit, to make two cross-members at these two locations.
The tops of these cross-members were trimmed, by means of jewellers’ snips, to follow the lower curve of the boiler and thus act as supports for the front end of the upper body. I clamped the two cross-members together and ‘tack-soldered’ their edges, to hold them together, while I drilled two holes to take the piston rods, which would hold the cross-members at the correct distance apart. The piston rods are represented by lengths of 1 mm copper wire. The initial layout of the module is shown below:
The valve rods, which were of thinner wire, were threaded through in the same way, between the piston rods. I can now see why more advanced modellers prefer nickel-silver to brass, as I found it was very satisfying to solder : once flux was applied, the solder ran like mercury across the surface!
I had planned to finish this post triumphantly, with a photo of the final assembly, but I have gone down with a heavy cold and, while I have cut out the various parts, I haven’t actually managed to fit them all together – bleary eyes and trembly hands conspire against such delicate work! This hasn’t stopped me from assembling the parts I have made, with a little help from Photoshop, to show how it will fit together (I assume!)
The slide bars are simply U-shaped ‘snips’ from nickel-silver sheet, held together by a wire running across the engine to represent the transverse lifting rod for the reversing gear. After a few failed attempts at soldering these, I decided it was too ‘fiddly’ for me and resorted to superglue. The problem with trying to solder these tiny parts is that adjacent joints persist in coming apart. I am sure all those amazing 2mmFS modellers find this sort of thing easy but I do not.
I suppose this doesn’t look like much, especially when compared with the amount of research I did, to find out where things should actually go! It does, however, fill a gaping space with some ‘realistic’ gubbins. I shall not continue behind the motion plate, because that area will be hidden by the sand boxes and, at some time in the future, I may wish to fit a gear-box and motor in the space.