Six years ago, in June 2017, I embarked on scratch-building a model of the Broad Gauge ‘Waverley class’ engine ‘Rob Roy’. The prototype was involved in an accident near Bullo Pill, where some of my wife’s ancestors were working for the GWR at the time.

 

‘Rob Roy’ – Accident near Bullo Pill, 1868

 

I took advantage of the fact that the boiler used for the Waverley-class was the same as that on the Gooch Standard Goods engines, for which the Broad Gauge Society (BGS) provide an etched-brass kit.. My old series of posts described in sometimes graphic detail how I constructed the kit, which involved rolling a boiler from rather thin brass sheet.

 

After completing the boiler from the kit, I was then faced with scratch building the chassis, which I also constructed from brass sheet.. The process was not without its problems, especially when fabricating the bicycle-style splashers over the large driving wheels but, after much trial and error, I ended up with a passable model.

 

One major compromise, however, was that I used wheels supplied by Hornby for their ‘Lord of the Isles’ model.  I chose these because they have the required 24 spokes and these exposed driving wheels create a large part of the ‘character’ of the Waverley-class engines. Unfortunately, the wheels are over-size and this not only means they stand a little too tall but also that they had to be more widely spaced than on the prototype. At the time, I felt I had to live with the compromise but now that I have the means to print my own wheels, I felt I should try something better.

 

My first scratch built model of Rob Roy, with Hornby driving wheels

 

 

Enter my 3D-Printer

 

The advent of 3D printing completely changed my approach to model building and I realise that there’s now no need to undertake the tricky fabrication of splashers from brass sheet and nor do I have to cut out the profiles of the sandwich frames by hand.

 

All I had to do was find a suitable drawing – I chose the one by E.W. Twining – and trace over it in ‘Fusion 360’ before extruding the drawings into 3D structures. My methods have been amply described in earlier blog posts but one of the important lessons I have learned is that it is possible to extrude the valances around the outer rim of the splashers without the need for any additional support during printing. This method worked successfully on my ‘Firefly’ model  and I applied it again here.

 

Extruded Frame over Twining 'Canvas' in Fusion 360

 

I then created a mirror image of this first frame and separated the frames at the appropriate distance, linking them be means of a buffer beam and drag bar, as shown below (rendered in Fusion 360):

 

3D model of chassis, rendered in Fusion 360

 

As on my previous model, I filled the open space under the front of the boiler by adding a motion plate and ‘suggesting’ part of the motion. Further back, any underpinnings are hidden by the sandboxes and splashers.

 

 

3D model of chassis with motion plate added

 

 

Printing the Components

 

The next step was to pass the various components to the Cura slicing software and then to my 3D printer, which created the following components:

 

3D printed chassis components, together with my boiler assembly,

constructed from a BGS etched-brass kit

 

Once assembled, the chassis looks as shown below, with the boiler supported by the curved motion plate. An advantage of designing the model in ‘Fusion 360’ is that the ‘fit’ of all the parts can be tested before committing them to print. This was especially valuable for this model, in view of the tight tolerances between the splashers and the driving wheels. Note that, as in the prototype, the hind wheels are flanged but the forward pair of drivers are not.

 

3D-printed Chassis and Wheels after assembly

 

Although I had felt reasonably content with my original fabricated chassis, mainly because I was unable to improve on the over-size wheels at the time, I realise now how ‘wrong’ it looks, when placed together with the 3D printed version!

 

 

My original chassis in front of the 3D printed version,

carrying my original brass boiler assembly

 

Overall, 3D-printing this chassis was a lot easier than using traditional methods, now that I am reasonably familiar with the ‘Fusion 360’ software. Of course, it is an option that was simply not available to me when I built my first model.

 

Now I have to add the brass finishing to the splashers and valances.

 

End of an era

 

This is probably the last model that I shall print with my ‘Geeetech’ E180 printer. It has given a few problems recently, first with the feed mechanism and now the hot-end temperature has become erratic. This printer uses a modular print-head, specific to this model, and Geeetech have informed me that replacements are no longer available.

 

After some thought, I’ve decided to buy a Prusa Mini+, partly because I prefer to buy a European product (although I have no complaints about the Geeetech company). I shall report my impressions once I receive the new printer.

 

Mike