At the end of the previous Part, I wrote that I intended to turn my attention to the chassis. Before that, I had broken off from work on the chassis, to give some thought to the problems posed by the curved splashers over the driving wheels.
Now that I have proven the technique of ‘hybrid’ construction, combining traditional etched brass model-making with 3D-printing, I’ve decided to pursue similar methods for the chassis. For wheels, I recovered a spare set from a ‘Mainline’ Dean Goods that I converted into a 2-4-0 ‘Stella’ a few years ago. My conversion was described in the April 2013 issue of ‘Railway Modeller’, These wheels have larger flanges than are desirable, so I shall probably replace them at a later stage but they are useful for setting the clearances for the splashers.
Rather than relying on measurements, I prefer to base my models on ‘templates’ that are derived from the actual components that I am using. In this case, I laid the chassis, with wheels attached, in my flat-bed scanner and made a scale image as the basis for my drawings
Scanned image of mainframe and wheels
I then ‘pasted’ this image as a background layer in my drawing program and drew the splasher outlines to fit around these wheels. I transferred my 2D drawing into ‘Fusion 360’, where I used the ‘push/pull’ tools to extrude the tops of the splashers so that they would ‘frame’ the wheels.
The resulting 3D model only took a few minutes to print, so it was easy to run off a test-print and check the fit before proceeding any further. This proved worth while, since my first print was a little too shallow to leave clearance for the valance to fit in front of the wheels.
While considering potential refinements to my initial print, I realised that some other features could be added to the footplate, including the tops of the springs, which appear from behind the splashers, and the sand-boxes, which are placed alongside the smoke-box. After adding these additional features, my 3D model appeared as shown below.
3D model of splashers with springs and sand-box
I extended the backplane of the print slightly below the top of the chassis, to provide a ‘tab’, so that the splasher assembly could easily be glued to the back of the mainframe.
One very welcome feature of 3D printing is that, in order to produce the splashers for the opposite side of the engine, it is only necessary to click on the ‘mirror’ command and the appropriate part is created automatically.
Once both sides had been printed, I glued them to the sandwich mainframes and inserted the boiler assembly between the frames, as shown below:
Hybrid brass / 3D-printed model of ‘Tantalus’
It was now time to turn back to brass construction and I cut out the etched valances provided in the BGS kit and glued them to the outer edges of the splashers to give the result shown below:
‘Tantalus’ after adding etched-brass valance
There are still many details to be added but I think my model has reached the stage where it allows the rather ‘gawky’ appearance of these early Broad Gauge engines to be appreciated. This might seem to be a short post but most of the work was in the planning - the actual printing and assembly only took a few minutes