By the end of Part Two , I had modelled all the most visible parts of the engine and felt tempted to stop there but many of the peculiarities of these engines were below the platform, so I had to keep going ‘down there’.

 

Photo by Snell of B&ER 4-2-4T No.42

 

Although I have collected quite a number of drawings and photos, there are still some difficulties in determining the layout of all the parts, especially since some drawings omit features and others show some profiles, without indicating their locations in three dimensions.

 

Well Tanks

 

I decided to start with the two well tanks, once below the boiler and the other below the coke bunker, since these are well displayed in the three-view illustrations from ‘The Engineer’ supplement, 1910, which I showed in Part Two.

 

I sketched the profiles by using the ‘Rectangle’ tool in ‘Fusion 360’ to trace over the end elevation illustrations. I then extruded the profiles to the lengths indicated on the side elevations. These steps are shown below:

 

Locating model well tanks against ‘The Engineer’ illustrations

 

The above drawings show the internal bracing struts inside the tank under the bunker, which served to reinforce the mounting for the ball on which the rear bogie was pivoted. While I have not modelled these completely concealed structures, they provided me with useful guidance on the placement of similar-looking braces at the font-end of the engine.

 

The drawings show that there were two upward extensions from the tank under the bunker, leading up to the filler caps. These structures also served to separate the crew footplate from the coke bunker itself, behind them. A tool box and brake handle were also placed above the footplate. According to Ahrons: “An arrangement of angle plates, 2ft. deep, was fastened to the side of the fire-box and to the front of the well tank. From this point to the back buffer beam there was no frame at all.”

 

I sketched the outlines of the tank extensions and the toolbox by tracing over the plan view from ‘The Engineer’ and extruded upwards from the sketches to match the illustration of the elevation. The results are shown below:

 

Coke Bunker with Toolbox and Tank Fillers

 

 

Front Bogie Mountings

 

Having secured the rear bogie on its ball and socket joint, it was time to turn to the front end. According to Ahrons: “The ball of the leading bogie was secured to the underside of the cylinders by means of a casting with wings, to which two horizontal tie rods were fastened ; the other ends of the latter were secured to the bogie side frames, and prevented the bogies from slewing round across the track.”

 

I attempted to identify these features from the front-end elevation shown in ‘The Engineer’ illustrations.

 

Front Elevation from ‘The Engineer’

 

I assume that the casting for the ball is the part I have coloured blue, while the ‘wings’ are the parts coloured orange. The tie-rods to the bogie frame can be seen extending outwards from pivots on these ‘wings’. Where, though, is the brace coloured red to be placed? It is shown crossing in front of the tie rods so, perhaps, as at the rear end, there were two braces – fore and aft of the tie rods.

 

I have enhanced the relevant area from the photo of No.42 above:

 

Detail from Snell’s photo of No.42

 

The photo clearly shows a reinforcing bracket on the bogie side fame and what looks like the end of a tie-rod just above the frame. It appears that there were bracing plates either side of the tie-rod, which may be what is represented on the front-elevation drawing. Unless anyone has any more information or I find another drawing, I have to go with this assumption.

 

I created the following support structure by first tracing the profile of the ball and the casting immediately above it, followed by using the ‘Revolve’ tool to create a cylindrical ‘body’. Then I sketched ‘wings’ either side of the central body.

 

For the bracket, I traced the front-elevation profile and extruded it, initially with a rectangular profile. I then used the ‘Cut’ tool across the extruded width to create the sloping sides seen in the photo above and the central slot through which the tie-bars pass. My result is shown below, with the component parts coloured as in the illustration above. I also show the completed model, assembled above the front bogie:

 

My interpretation of the front bogie support frame

 

With the well tanks and bogie attachments in place, the underside of my model now looks like this:

 

My model underside with well tanks in place

 

As an aside, I think this underside view demonstrates why Dean failed in his attempt to create a narrow (standard) gauge version of a 4-2-4 tank engine. There was no room for the large well tanks so he had to resort to large side tanks, which were a source of severe instability. I have previously modelled Dean’s experimental No.9, as described in my Pre-Grouping blog.

 

There’s a lot more detail still to be added to the underside. To gain an overview, I ‘mirrored’ one half of the split plan-view from ‘The Engineer’ and then colour-coded various elements – blue for frames, orange for crankshafts, green for valve gear, and red for wheel bearings. I made a couple of ‘corrections’ to the ‘mirror’ process by moving the cranks on one side to represent ‘quartering’:

 

My Colour-coded plan view, derived from ‘The Engineer’ illustration

 

As I began to examine this underside view in conjunction with the various elevations, I realised that the complex array of brackets and plates was not going to be easy to unravel! On this engine, the motion is very visible in side views, so I cannot escape modelling its main features.

 

It has become clear that it’s going to take me some time to work out how all these parts fitted together in three dimensions, so I’ve decided to take a break before starting on modelling the motion and various underpinnings. This will a new area for me, since I have neglected any detailed representation of the motion on the engines I have designed previously.

 

Mike