In my previous post, I described making a 3D print of a Broad Gauge 1st / 2nd composite carriage, based on a prototype dating from 1854. With a bit of ‘Photoshop’ colouring, the 3D model of the body looks like this:
3D-printed Broad Gauge Carriage Body
After printing the body, I have now turned my attention to the under-frame and running gear.
I have mentioned before the many useful ‘out of copyright’ books that I have found on the web, mostly in the ‘Internet Archive’. My latest ‘find’ is a book by Daniel Kinnear Clark called ‘Railway Machinery’, published in 1855, which has proved something of a ‘gold-mine’.
Amongst all the information about locomotives, track, etc., there are details of components such as wheels, axle-boxes, and springs, together with excellent drawings of many early carriages, including some early GWR Broad Gauge designs.
Finding the 1st volume (text) on-line was straightforward but Vol.2, which contains the plates, proved more difficult, since many scans fail to copy the large ‘fold-out’ drawings. Fortunately, I eventually found a free download from Google Books at https://books.google.co.uk/books?id=QQ0cqi6y9vYC
For some reason, I could not download this book from my usual Firefox browser but Internet Explorer worked: Just click on the wheel icon, at top RHS of the page, and select ‘Download PDF’ from the drop-down menu.
These plates show details of the Normanville axle boxes, used on many early GWR carriages, and also the various wheel patterns, used at different periods, as shown below:
Wheels and Axle-Boxes – from Daniel Kinnear Clark ‘Railway Machinery’ 1855
I also found detailed drawings of a GWR Broad Gauge 1st class carriage, which includes details of the longitudinally-divided central compartments, the underframe, and the running gear.
GWR 1st-class Carriage – from Daniel Kinnear Clark’s ‘Railway Machinery’ 1855
By combining information from these drawings with that contained in the BGS Data Sheets, available to members of the Broad Gauge Society, I was able to prepare scale drawings in sufficient detail to design a 4mm-scale model.
As usual, I found that the research took rather longer than actual model building but it is good to retrieve so many otherwise ‘lost’ pieces of information.
As regular readers will know, I do not go for a high degree of mechanical precision in my modelling but like to create a general impression of the prototype, with as many correct dimensions as I can achieve, with my limited equipment.
In creating the chassis, my first step was to prepare 2-dimensional drawings, using my favoured ‘Autosketch’ software. My end result is shown below:
Sketch of Broad Gauge 6-Wheel Chassis
Now, I had to decide how to turn this design into a 3D-printed model. Since it was over a month since I last used my ‘Fusion 360’ software, I had forgotten a great deal about how to begin but, fortunately, I have used my other blog to keep notes on my methods, as I went along. These proved invaluable in jogging my memory over many important ‘lessons learned’.
It’s hard to know where to begin when modelling the complex assembly of parts that make up the running gear of a railway carriage. Should I model the individual components separately and then glue them together, as when using traditional design method? As an experiment, I decided to try exactly the same technique as I used for the body, starting from the ‘floor’, immediately below the main body of the carriage and then using the extrusion (‘push-pull’) tools in ‘Fusion 360’, to create the sole-bars and head-stocks as an inverted open-top box. I then took my 2D drawing of the sides, including springs and axle-boxes, and ‘pasted’ the (DXF) drawing over the sole-bars, exactly as I described, in the notes referred to above, for placing the window-openings on a carriage body.
It would have been extremely tedious to design all the details individually for each wheel but, fortunately, I am becoming more adept at using the various ‘move’ and ‘copy’ tools within the ‘Fusion 360’ software. I must admit that I’m not yet completely au fait with the precise meanings of terms like ‘bodies’ and ‘components’ but, with a little trial and error, I managed to select groups of items, such as spring leaves, and to link them together into a single entity, which I could then copy and move to locations aligned with other wheels.
The copying process is a little cryptic, since it depends on a small check box at the end of a list of options for the ‘move’ command.
Eventually, I was able to complete a reasonable representation of the sole-bar and its various fittings on one side of the chassis. Then, I thought that I should be able to mirror-image the work I had done, to create the opposite sole-bar with little extra effort. An initial ‘Google search’ for how to do this was somewhat dispiriting , until I realised that I was reading some old material, but a later ‘upgrade’ to ‘Fusion 360’ has made the task relatively simple.
I first ‘cut’ my chassis into two halves, along its length, and deleted the half on which I had not added the details. Whereas the ‘move’ and ‘copy’ commands appear in the ‘Modify’ menu, the ‘mirror’ command took some finding, since it lies in the ‘Create’ menu. Once this was sorted, it was simply a question of selecting a plane to act as a mirror and the other half of the chassis ‘magically’ appeared on the base plane, a little distance away from the original. I then used ‘move’ to bring them together, followed by ‘Assemble’ to join up the halves into a single entity again.
Stages in creating 3D Model
Since I usually work by ‘following my nose’ (i.e. ‘empirically’), I only realised at this stage that it would be a good idea to provide holes in the axle-boxes, to accept pin-point wheel bearing cups. All that was needed was to draw a circle, centred within a face of the axle box, and use the ‘push-pull’ tool to take the opening across the body to the outer face of the opposite axle-box. One of the advantages of my ‘all-in-one’ approach is that the two sides are aligned automatically. I also opened slots in the floor to allow the wheels to protrude into wheel-boxes within the compartments, as on the prototype.
Preparing the Printer
A cause for concern was that the axle-boxes and springs overhang the area defined by the main frame members. This is a problem when 3D printing, because the final model is built up in layers and the printer head cannot lay down filament over empty space! For my experimental prototype, I decided to let the Cura ‘slicing’ software deal with the problem in its own way, by selecting to allow it to add ‘support structures’, where it considered them to be necessary.
‘Cura’ Layer View (152 layers) after ‘Slicing’
The good news is that my first trial print went smoothly and quickly – well under an hour to complete. I am now gaining much more confidence in the printing process and was content to leave the machine to its own devices ‘for the duration’.
In fact, despite some of my ascerbic comments over teething troubles with my Geeetech E180 printer, it is now proving extremely simple to use. I simply copy the ‘gcode’ file produced by the ‘Cura’ software onto an SD-card and place this into the slot in the back of the printer. Switch ‘on’ and select the required model on the touch screen of the printer, press ‘Print’ on the touch screen, then sit back and watch or get on with something else. Since the printer works from an SD card, it does not tie-up my computer when printing so I can get on with other modelling tasks.
The fans start up and the printer pauses for a while, until the head reaches printing temperature (200°C) then immediately starts printing. I now set the ‘Cura’ to add a ‘brim’ around the model, which has two advantages: It (i) fixes the model securely to the (unheated) print bed, and (ii) ensures that any initial ‘blob’ of filament, as the printing starts, goes onto the brim rather than the model.
Looking back, it seems strange that I initially experienced poor adhesion of the model to the print bed as I now have the opposite problem and find it difficult to remove the model without a lot of easing with a knife blade.
My first prototype took under 1 hour to print but was too fragile and two of the axle-boxes broke off, while trying to remove the chassis from the printer bed. The springs had also become muddled with the support structures and were, again, too lightly constructed for a 4mm scale model. The lesson was that I needed to ‘beef up’ the thickness of some of my structures, in order to use plastic for under-frame construction.
Now that I am more familiar with using the ‘Fusion 360’ software, I found it was quite easy to increase the thickness of various components, by selecting the faces I wished to move and then using the ‘push-pull’ command to make the necessary adjustments. The ‘thicker’ versions can be seen in the last frame of my illustrations of the process, above.
Because there are a lot of small details in the model and the overall print time was relatively short, I decided to select the ‘extra-fine’ mode when printing. This lengthened the print time to about 2h 20m but did result in a finer surface finish.
The Printed Model
I’m pleased to write that the finished model exceeded my expectations. I had bought my printer as something of a ‘toy’ which I could use to explore a new technique and, perhaps, make some small component for my railway. I had never envisaged building complete carriages and am pleasantly surprised by how it has turned out.
The underside view of the chassis, as removed from the printer bed is shown below. There were a few fine ‘fingers’ of filament sprouting from various corners and a finger-nail proved to be an excellent tool for removing these. Otherwise, the print had worked well, including the over-hanging springs, which I had thought might cause problems. The ‘extra-fine’ mode showed almost no layering effect at all on the vertical faces of the sole-bars.
3-D Printed Under-Frame
Wheels from the Broad Gauge Society fitted neatly between the axle-boxes and I soon had a ‘rolling’ chassis, as shown below:
3D-printed ‘Rolling’ Chassis
Finally, I brought together the chassis with the 3D-printed carriage body, to complete the overall model of an 1854 Composite carriage, with its internal partitions dividing the 1st class compartments into side-by-side pairs.
3D-printed Model of Broad Gauge 1854 Composite Carriage
With a coat of brown paint, it should fit well into my planned Mail Train. I should be able to use a very similar chassis for my planned 2nd class carriage, although this will also require brake gear.