At the end of the previous part, I had printed the main body components but was experiencing difficulty in printing small boiler fittings. The difficulty was that, on their own, these had no flat surface to lay on the printer bed. My next idea was to ‘slice’ these components just above the curved flanges that fit around the boiler and print the upper and lower parts separately, so that they could subsequently be glued together across their flat faces.

To my surprise, the tiny components printed remarkably well and could be glued together as I had anticipated. Considering that my E180 printer had only cost me £185 (it was on offer at the time), I considered this a remarkable achievement. Below, I show a couple of these tiny parts in the palm of my hand.

3D-printed Dome & Safety Valve Cover

I have always tried to arrange items for printing so that there are no overhangs, which are a major problem for fused-deposition printers like mine. This is because they cannot lay down plastic filament over empty space. I’ve found, however, that my printer appears to be fairly tolerant of small overhangs, where the new layers can adhere to adjacent layers in the same plane. I found that this was the case when printing flanged wheels, when the flanges were reproduced without any support below them.

As another step along these lines, I decided to try printing the flange below the chimney of my current model as an integral part of the smokebox and found that it worked very well. I followed this by re-printing the boiler with protruding flanged bases on which to mount my flat-bottomed dome and safety-valve components. The revised boiler and fittings printed successfully, as shown below:

Boiler & Smokebox with flanged mounting points

Printing the chimney raised some interesting new challenges. Since the mounting flange was already printed on the smokebox, the main task was to produce the flared cap. I started by extruding a cylinder and then, as shown below, used the ‘fillet’ and ‘chamfer’ tools in ‘Fusion 360’ to create a suitable cap.

Stages in 3D-printing a flared chimney

Some of the finer points are beyond the resolution of my printer but it’s good to know how to do them. Once I had worked out the methods, the actual design went very smoothly and the chimney printed successfully in less than 10 minutes. When printing, I included a wide brim as a support structure at the base, in case the chimney toppled during printing. I suffered this experience with one of my boiler test prints, when I forgot to provide a brim and ended up with a messy blob of plastic on the printer bed!
 

Chimney with support brim on printer bed

It was by way of light relief from the design effort I had expended on the chimney that I also printed the smokebox front, with a sloping cover for the fronts of the cylinders. The smokebox door has a very shallow curve, which is obviously layered in the 3D print but I’m hoping that priming and painting will minimise the visibility of the steps.

The next, more complex task, was to print the cab. I had decided to provide the later style of cab with a roof, rather than the vestigial version originally fitted by Armstrong. It is said that Armstrong believed that enclosed cabs were unhealthy, which was probably true when coke was the fuel and considerable amounts of carbon monoxide were produced.

I designed the cab so that it would lie on the printer bed with the flat front downwards. The first stage was to extrude the cab front and rectangular sides. I then copied a drawing of the side of the cab, including the shape of the side openings and the wheel arch. I overlaid this drawing as a DXF import over the cab side and used the ‘push-pull’ tool in ‘Fusion 360’ to open out these shapes. I also added an arc to the top of the cab front and extruded this to form the roof.

Having extruded a drawing of the outline of the back-head and used the ‘fillet’ tool to create the rounded edges, I started adding representations of various controls and pipes, with reference to photographs. In 4 mm scale, I feel it is sufficient to trace the general outlines, rather than attempting to add too many details. I illustrate the steps below:

Stages in printing the Cab

After printing all these items, none of which took very long to print, although the design time was much longer, it was time to see if they would all fit together and clear the 00-gauge wheels. There are rather large gaps around the wheels, which will be filled when I add the tops to the wheel arches, either from brass strips or plasticard.

current stage of my Armstrong Standard Goods

I think the result has captured the ‘look and feel’ of Armstrong’s prototype rather well. There are of course, many fittings still to be added but I think my work so far has demonstrated the feasibility of making attractive and robust models by means of a combination of brass sub-structure and 3D-printed overlays. This is not an example of skilled model-engineering but it demonstrates that pleasing results can be obtained from low-cost equipment operating in a domestic environment.

The difference in ‘character’ between the Armstrong Standard Goods and its successor, the Dean Goods, came across very clearly when I placed my model head-to-head with my ‘Mainline’ Dean Goods, as shown below:

my models of Armstrong and Dean Goods engines head-to-head

The boiler of the ‘Dean’ is both shorter and higher in pitch than the earlier design, which give it the ‘pugnacious’ look that I once commented upon in an earlier post, The ‘Armstrong’ has the less robust look of an engine from the mid-nineteenth century. One of the pleasing aspects of ‘rolling your own’ is that you do not have to accept the compromises that are inevitable when relying on ‘bought in’ components, which are rarely designed to meet the needs of the modeller of 19th century prototypes.

Mike