At the end of my last post, I felt that I had solved all the main problems associated with building my Armstrong Goods engine, although a lot of detailing remains to be done.
To complete the model, I needed to add a tender, which I intended to contain the drive unit. I have made several powered tenders based on 'Hornby' ring-field mechanisms, around which I used components from either plastic or white metal kits. I have used two different 'Hornby' mechanisms: type X9105 with 7' 6" + 7' 6" scale wheelbase and type X2024 with 6' 6" + 6' 6" scale wheelbase. In both cases, only the outer axles are driven, while the centre axle is free running.
There is a very useful overview of GWR Tenders by Jim Champ on the GWR.org website. In this, I read that “The earliest standard-gauge tenders, like the locomotives they were attached to, were a rather motley collection from a variety of manufacturers.” From 1866, however, Swindon-built tenders had iron-plate frames and most had the now standard 6' 2" + 6' 10" wheelbase. 306 were built, typically 1800 gallon capacity.
Typical Armstrong Tender
Note that the overall wheelbase of these tenders was 13 ft, which matches the 'Hornby' X2024 drive unit, in which the centre axle can easily be moved to represent the unequal spacing of the prototype axles. There are many photographs of Standard Goods engines with these tenders, some with or without coal rails but often with remarkably high loads of coal which, in model form, can be used to cover the drive motor! A particularly spectacular example is shown at Widney Manor Station on the Warwickshire Railways website.
I found a drawing of an Armstrong tender at Fig.62 in Russell’s ‘Pictorial Record of GW Engines’, which I used as the basis for my model. There are many differences in detail between different photos but I decided that this drawing was a fair representation of the type.
Whereas my practice in the past has been to prepare my drawings in a 2D program, such as ‘Autosketch’, I decided to try a new approach by using the drawing tools within ‘Fusion 360’, which meant that all my design work was done within the same software package. This proved very successful, as these drawing tools have many features that made it easy to align and replicate the various elements of the drawing. To guide my drawing, I used the ‘Insert canvas’ feature on ‘Fusion 360’ to display a copy of the drawing in Russell, as a background over which I could lay out my own drawing.
By following this procedure, I drew one side of the tender as shown below:
My Drawing of Tender Side in 'Fusion 360'
Drawing all those rivet and bolt heads could have been extremely tedious but the ‘move and copy’ commands in ‘Fusion 360’ made it a lot easier! I drew one short line of rivets and then duplicated these, as necessary, to form long rows or regular arrangements, such as those around the hornguides. A line of five quickly duplicates to 10, then 20, and so on.
Once I had completed the drawing, I could use the ‘push-pull’ tools to raise all the necessary features by appropriate amounts, to create a 3D drawing of the complete tender side. The selection tools make it easy to select many similar feature at the same time, so that these can be raised all together. The resulting 3D model is shown below:
Tender Side extruded from 2D Drawing in 'Fusion 360'
I also continued my method, as used in other models, of designing the complete tender as a ‘kit’ of separate parts that could be printed and tested individually, without involving long print times. Having drawn one side, it only required a single click on the ‘Mirror’ command to create the opposite side
The front and back of the tender were created by using exactly the same methods and all the parts were transferred separately to my ‘Cura’ slicing software to prepare them for 3D printing. Even the long sides only took around 20 minutes to print, so I could make minor adjustments to the drawings without any very long delays.
Once I had printed the individual parts, I could join them together by welding inside the corners with a soldering iron bit set to 210°C. Then I lowered the open box structure over my X2024 drive unit. It proved to be a very close fit and I shall have to re-arrange some of the wiring to pack everything in, within the narrow constraints of the overlays.
Tender Sides fitted around Motor Drive Unit
It is clear that the coal load has a lot of work to do!
A highly visible feature of early tenders was the profusion of tool boxes that they usually carried, either all on the top plate or, in some cases, on a broad shelf immediately above the back buffer beam. In a study of GWR tenders published in the Broad Gauge Society magazine ‘Broadsheet’ vol.18.14, the authors speculated that these extra boxes held locomotive screw jacks.
I 3D-printed a suitable collection of these boxes on a top-plate for the tender, which will also form a base for the considerable ‘coal load’. The two slots, adjacent to the central cut-out for the motor, are to fit over raised strips on top of the motor block. The following photo shows the tender top loosely positioned on top of the tender body, to check the fit of these components:
Tender Shell with Four Tool Boxes & Filler Cap (in primer)
In order both to conceal the motor and provide a base for a coal load, I first wrapped the drive unit in 'cling film'. This was to protect it from water and dust during the following process. I then cut a small rectangle of plaster bandage (‘Mod-Roc’), soaked it in distilled water, and wrapped it closely around the upper part of the motor unit. I laid my printed top plate over the bandage and weighted it down to hold everything in place while the bandage hardened overnight. I only used one layer of bandage since I did not want too rigid a structure but simply a conformal cover that would prove a suitable surface for adding ‘coal’ chips.
Once the bandage had set, I trimmed away all the excess material but left a layer of cling film inside the bandage across the top of the motor. I then painted the exposed surface with dull black acrylic.
The final task was to paint the tender sides and top with two coats of 'Precision Paints' 1881-1906 GWR Green for the sides, Indian Red for the outside frames, and Black for springs and other parts. The final result is shown below:,
My ‘Armstrong’ Tender with base for adding ‘coal’ load
I realise that many people do not like tender drives but there is no reason why my modelling methods could not be applied to any other type of chassis, if I decide to make changes in the future. The more recent 5-pole 'Hornby' motors run a lot more smoothly than earlier designs and I note that ‘Strathpeffer Junction' models list various ‘upgrade’ kits based on the use of CD/DVD motors, although these are currently not in stock. I may try one of these at some stage, to see if they make a significant improvement.
I need to consider the addition of lining and will do this when I complete the detailing of my Armstrong Standard Goods locomotive. In photographs of the prototypes, the lining always seems quite subdued and I feel that many models suffer from over-prominent lining. I shall probably make my own, using my Silhouette cutter, as described in earlier posts.