Over the summer, I had little time for modelling, although I did continue with my reading, especially about the early engines of the GWR. Although these have been widely dismissed as ‘freaks’, this term only really applied to a very few examples and most were simply too small, because the manufacturers were attempting to meet Brunel's weight specifications, which were virtually impossible.

 

At that time in the late 1830s, locomotive design was still in its infancy but a few manufacturers were working hard to raise standards of construction. One that stood out during my reading was Sharp, Roberts & Co. and especially the efforts made by their co-founder, Richard Roberts.

 

Although little known in the locomotive field, Roberts was a prolific inventor in the field of textile machinery, which was the back-bone of the industrial revolution. He had an excellent grounding in engineering from his time at Henry Maudslay’s works, which was at the forefront of contemporary engineering practice.

 

One of Roberts’ many innovations was the use of piston valves, which he applied to three engines supplied to the GWR – named ‘Lion’, ‘Atlas’, and ‘Eagle’. Unfortunately, these were not a success, possibly because of differential expansion between the valve components, which led to excessive steam leakage but, otherwise, these were very sound engines and performed well, once new cylinders had been fitted. Two of these engines survived in branch-line use until 1872, by which time the broad-gauge was in full retreat, with only the West Country main line lingering on until 1892.

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I was interested to note that, like ‘Aeolus’, which I modelled earlier this year, ‘Eagle’ also worked on the Abingdon branch, which happens to be my home town. I thought, therefore, that ‘Eagle’ made a good candidate for my next early broad-gauge model.

 

The spare part for my Geeetech printer arrived from China more rapidly than I had expected, so I was ready to go but, first, there is the task of creating the 3D model in ‘Fusion 360’

 

My Modelling Work-flow

 

It’s a while since I have created a new model, apart from re-furbishing a carriage, as described on my pre-grouping blog. During the interval, I seem to have almost subliminally developed a fairly rapid design work-flow.

 

As I mentioned in an earlier post, ‘Fusion 360’ is designed around the concept of starting from an overall design and then breaking it down into components - a ‘top down’ approach. In my earlier attempts, I used to create the individual parts separately and only bring them together after printing.

 

Now, especially with these early engines, where prototype information is limited, I start from an existing drawing and then extrude each component in turn from the drawing, before bringing them all together within a single overall project file in ‘Fusion 360’.

 

What I have found is that working in this way doesn’t need much computer modelling expertise, beyond what is needed to create a two-dimensional (2D) drawing.  This is because most engine components can be created either by linear extrusion from a 2D drawing or by rotating a profile from a 2D drawing. There is rarely any need to consider more complex shapes involving double-curvature.

 

This method also means that I do not need to make any of my own measurements but simply to rely on the drawing being accurate and traceable by means of the ‘line’, ‘circle’, and ‘arc’ drawing tools in ‘Fusion 360’

 

With this simple concept in mind, I find it surprisingly easy to put together the main elements of a new locomotive in a remarkably short period of time – and it can all be done while sitting in an armchair 🙂

 

My Modelling Method, Step-by-Step.

 

This post describes the steps I have taken in order to create a 3D model of ‘Eagle’ in ‘Fusion 360’, although the methods I shall describe have general application.

 

In the case of ‘Eagle’, all that I had to work from, apart from some references to cylinder and wheel sizes, was the very good side-elevation drawing by E.T. Lane, the young apprentice who provided us with most of our knowledge of early GWR engines.

 

Sharp, Roberts & Co. ‘Eagle’, drawing by E.T. Lane, 1849

 

My first step was to import this illustration into ‘Fusion 360’ as a ‘canvas’. This canvas represents the ‘top level’ concept of my model, which I then break out into individual components.

 

Fusion 360 – Top-Down Assembly

 

I could now start to create ‘components’ by using the ‘Fusion 360’drawing tools to trace over elements of the drawing by Lane.

 

I started with the frames, which are of an interesting design, as used in many of Sharp, Roberts & Co. ‘standard’ 2-2-2 engines. The sloping frames appear to have been used to avoid the need for excessively long supports for the small carrying wheels.

 

My own first drawing of one of these frames in ‘Fusion 360’, produced by copying over the ‘canvas’, looked like this:

 

Drawing the Frame over the ‘canvas’

 

Working on the imported ‘canvas’, I selected the ‘draw’ mode in ‘Fusion 360’and drew a line from the marked start point to the first curved section. Then, I changed to the ‘3-point arc’ tool for the next segment, then back to the ‘line’ tool, and so on, until I had completed the circuit of the frame. With practice, this can be quite a rapid process, as each segment follows the end of the previous one.

 

Once a ‘closed’ outline has been created, it is only necessary to click on the enclosed area and select the ‘push-pull’ tool (shortcut key ‘Q’), to extrude the frame into a solid 3D ‘component’.

 

I moved this first component off to one side, then created a duplicate for the opposite side of the engine. Correct positioning of the two frames can follow later.

 

Next, I created the boiler.  Information from the RCTS booklet on broad gauge engines told me that the diameter should be equivalent to 3’ 6” (i.e. 14 mm in 4 mm scale), so I used the drawing tools to create a 14 mm diameter circle. The cladding lies outside this diameter, so I used the ‘offset’ tool to create another circle 0.75 mm (or 2.5” on the prototype) outside the first. Then I clicked ‘Q’ to extrude the enclosed space between the circles to the length of the boiler – in this case 8 feet (32 mm in 4m mm scale). Then, I used the ‘move’ tool to align the boiler between the frames previously created.

 

Next came the smokebox, which has a larger diameter than the boiler. I took account of the difference by using the ‘canvas’ and created another circle. I added a couple of tangential vertical lines each side of the circle, to create an enclosed space corresponding to the front profile of the smokebox and extruded this to the length of the smokebox. By working over the ‘canvas’, there is no need to make measurements – simply extrude until it corresponds with the ‘canvas’, as shown below:

 

Extruded 3D Components

 

All the coloured items are ‘solid’ (3D) bodies, with their dimensions determined by extruding over the ‘canvas’ – no measurements needed apart from the diameter of the boiler inside the cladding.

 

The firebox was created in exactly the same way as the smokebox and so, after a remarkably short time, I had created all the major components by repeated copying from the ‘canvas’. As mentioned above, I found it easier to move each completed component to one side before starting the next one.

 

After moving them all to one side, the 3D model in ‘Fusion 360’ looked like this:

 

 

Major Components brought together in ‘Fusion 360’

 

Creation of the boiler mountings needs a different tool – the ‘revolve’ tool - but the method is much the same. For the chimney, dome, and safety valve cover, I drew lines and arcs over half of the profile, as shown below:

 

Creating the Chimney

 

A touch of the ‘revolve’ tool and I had a ‘solid’ chimney, complete with flared top and bands between the sections of the prototype. The dome and safety valve followed by exactly the same process, so that my model in ‘Fusion 360’ now looked like this:

 

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Assembled body in ‘Fusion 360’

 

So far, the ‘bones’ of the engine had come together very rapidly but, as always. The ‘devil is in the detail’. Fortunately, ‘Fusion 360’ provide several tools that automate repetitive adding details.

 

One example of this automation is provided by the spoked wheels. I started by drawing circles over the boss and rim of the driving wheel shown on the ‘canvas’. I then used the line tool to trace over the profile of one of the spokes, as shown below:.

 

Drawing a Wheel – First Spoke – in ‘Fusion 360’

 

Completing the wheel is then simply a matter of using the ‘pattern on path’ tool in ‘Fusion 360’, to make the required number of spokes, all following the circular path of the rim. This automated process ensures a pattern of identical spokes, evenly distributed around the wheel – all at the click of a mouse!

 

One carrying wheel followed, by the same process, and I then copied the required number of wheels and moved them into their correct locations around the other completed components.

 

I used the same automated process to create the planked wooden cladding around the boiler and firebox. I simply had to create a single plank and then use the ‘pattern on path’ tool to produce a complete array of planks all around the boiler and around the top and sides of the firebox. The model was now looking like this in ‘Fusion 360’:

 

Wheeled Model in ‘Fusion 360’

 

Apart from detailing, the model is now almost complete except for one glaring omission – splashers!

 

These peculiar bicycle-like splashers, as used on many broad-gauge engines can be a nightmare for modellers because of their complex shapes and close tolerances around the wheels.

 

Again, I think the difficulty is actually less when using 3D-modelling than when using brass or card but it still needs careful thought. I have, however, created splashers of this type before, on my models of a Gooch Standard Goods and of ‘Aeolus’, so I shall finish this post here and continue with the detailing next time.

 

Mike