A comment on my recent post about modelling Rocket reminded me that my first scratch-built locomotive was an Armstrong 2-2-2 that I constructed 10 years ago and described in ‘Railway Modeller’, July 2014 , as ‘Simply Victorian’. I explained in that article that I was encouraged by a drawing of one of these engines in Russell’s ‘A Pictorial Record of Great Western Engines’ with the caption comment that: "The utter simplicity of these early engines can be seen." The idea of ‘simplicity’ appealed to me!

 

Later, when contemplating additional engines for my ‘North Leigh’ layout, I considered other Armstrong types, including the earlier ‘Sir Daniel’ class. At that time, I wrote of my first model that “It really was simple to build - basically a brass tube over a brass plate, with a very simple 'chassis' to hold a set of wheels at the right distance apart! It was really just a wagon that can be pushed along by a motorised tender. I would recommend an early 2-2-2 as a good subject for a first attempt at locomotive scratch-building.”

 

Principal Components of my 1st model

 

Whereas the 'Queen / Sir Alexander' class that I chose to model were the last engines designed by Joseph Armstrong before his untimely death in 1877, the 'Sir Daniels' were his first standard-gauge engines built at Swindon, starting in 1866,

 

Writing in 2015, I decided that “In summary, I can see that I could make a model of a 'Sir Daniel' by using exactly the same methods that I used for 'Queen'. At the moment, I feel tempted but concerned that the two would end up looking too similar! If I do tackle a 'Sir Dan', I shall have to choose a prototype with significant differences from my existing model”

 

I felt at that time that my options were limited by what I could make using the traditional methods of brass-sheet construction. Since then however, my horizons have widened considerably following my adoption of 3D printing which greatly eases the problems associated with matters such as open splashers and other awkward features.

 

Sir Daniel No.378 in ‘as-built’ condition

 

One elephant remains in the room, however, and that is the fact that a ‘00’ gauge model really is a ‘narrow gauge’ model, within which true-to-scale boilers may not fit! In the case of my ‘Queen’ model that meant taking jewellers’ snips to the brass sheet I intended to roll into a boiler – fortunately, it still rolled successfully! It also meant that I had to adopt covered-in splashers to hide the gaping hole that I had created, so my model had to be of the later Dean rebuild of the type.

 

Now, with 3D printing, I felt able to look back to the original design of 1866 for an engine that would be significantly ‘different’ from a rebuilt ‘Queen’ prototype of 30 years later. I still had to take into account the constraints of ‘00’ gauge, with a back-to-back dimension between the driving wheels of only 14.4 mm (3’ 7” at prototype size) against a boiler diameter of 4’ 2” (plus cladding).

 

According to RCTS ‘Locomotives of the GWR’,Part 4, the main dimension of interest to a modeller were:

 

‘Sir Daniel’

• Cylinders. Diam. 17" Stroke 24"
• Boiler. Barrel 11’ 0"
• Diam. outs 4' 2"
• Pitch 6' 11".
• Firebox. Length outs 5' 4"
• Wheels. Carrying 4' 0".
• Driving 7' 0"
• Wheelbase 7' 8" + 8' 4", total 16' 0".

 

For comparison, the later ‘Queen’ class had shorter boilers but larger fireboxes and a longer wheelbase of 17’ 6”.

 

Creating a Model.

 

I started by considering the design of the boiler and the need to accommodate ‘narrow gauge’ driving wheels. My references were the photograph of ‘Sir Daniel’ as originally built, shown above, and a drawing by Jim Champ, which I imported as a canvas into ‘Fusion 360’

 

Usually, I like to make the boiler from a brass tube and add a 3D printed cladding, as on the prototype. In this case, however, I had to accommodate the driving wheels, so I decided to 3D print the boiler itself and add weight by lead strips afterwards.

 

After some thought, I decided on the following procedure:

 

1. create a cylinder of length 44mm and diameter 18mm, to represent the external dimensions of the boiler plus its cladding

 

2. create a pair of 28mm diameter driving wheels, with additional 0,5 mm flanges, and mount these either side of the boiler at the ‘00’ back-to-back separation of 14.4 mm

 

3. Assemble these parts into their correct locations within Fusion 360 to create a visual impression of what modifications would be required to the boiler model, as shown below..

 

Tackling the 00 gauge Boiler Problem

 

I realised that the diameter of the cut-outs in the sides of the boiler would have to be wider than this, because it would simplify the design of the splashers, if I could also recess these into the sides of the boiler. I drew a circle of the required diameter in Fusion 360 and then used the ‘extrude’ tool in ‘cut’ mode to create recesses of the depth required to accommodate the driving wheels.

 

Cutting recesses for driving wheels and splashers

 

After dealing with that problem, the rest of the construction followed a familiar course. I extruded a pair of outside frames from the drawing canvas and set these at a ‘true scale’ distance apart. This means, of course, that the driving wheels are inset, relative to the prototype, but the overall arrangement of the locomotive is correct. If I wanted to run the engine on scale track, this would be possible, simply by extending the driving axles. At this stage, the frames are purely ‘cosmetic’ and I shall consider the design of the real chassis later.

 

All the other parts were similarly extruded from the drawing or, for the dome and safety valve covers, I used the ‘revolve’ tool on a profile sketch.

 

One thing I always have to bear in mind is the ‘printability’ of a 3D model created in Fusion 360. I aim to divide up the component parts, so that each one has a flat surface to lie on the printer bed, from which the rest of the structure can be ‘grown’, For example, I provide flat plinths on the boiler, so that the various boiler fittings can be printed from flat bases. The ‘exploded’ view below shows the collection of parts that can be printed individually.

 

Components shown separately in Fusion 360

 

As usual, I also like to do a ‘test fit’ of all the components by assembling them within Fusion 360 as a final check before printing – they can be seen against the ‘canvases’ from which the parts were extruded below:

 

My model of ‘Sir Daniel’ assembled within Fusion 360

 

The next stage will be to design a chassis, which will be based on an inside-frame for the wheels. As in the case of my existing ‘Queen’ model, I intend this one to be driven from a powered tender.

 

Mike