Gauge 1 Diesel Multiple Unit

This page last updated: 8 October 2018.

Having begun the construction of my front garden railway on a postage stamp (intended to reflect the Rhymney Valley line in south Wales from around 1964) at the start of 2018 I needed to resolve how it carries passengers.  The Rhymney Valley line was converted to diesel multiple units in around 1958 and, with the help of Noel on the WRRC forums, the immensely detailed www.railcar.co.uk, and my memories, I determined that I needed a class 116 DMU, gangwayed (i.e. converted to have a corridor running all the way through) in all blue livery except for yellow-painted ends.  However, no-one makes such a beast so I had to construct one myself.  I began work from these drawings:
Stuart Mackay of www.railcar.co.uk helped me with additional pictures and Chris Moxon of preserved.railcar.co.uk helped me get in contact with Alan Pitt of the Great Central Railway near Nottingham where Dave Watts, the co-owner of a class 116 DMU (one of only two that remain) very kindly allowed my to take detailed pictures and measurements.

For the modelling part, I joined the Gauge 1 forums to ask for advice.  David Halfpenny pointed me towards David Leech, a Canadian modeller who has a retirement business scratch-building coaches and has attempted to build a class 121 DMU using 3D printing.  David Leech has given me lots of great advice on the use of 3D printing, the more traditional bent aluminium sheet method and many, many other aspects of Gauge 1 coach building.  I also purchased a copy of "Carriage Modelling Made Easy" by David Jenkinson which describes another method for making coaches.  I decided to 3D print the ends and initially I thought I would make the body of folded aluminium sheet but in the end it turned out that 3D printing would work for the entire body.  Drive will be provided by a couple of fosmotors on one bogie, the power and control for which David Leech believes can be hidden underneath the DMU.  Here's what I think I have to do:
Having never done this before lord knows how it is going go turn out.  But I have to start somewhere.

Drawing

I have begun collating the dimensions of the vehicle.  These are based on the drawings from www.railcar.co.uk but have been much enhanced by a visit to the Great Central Railway for a detailed photographing/measuring session.

Motor
                Open Second Body
Cabin dimensions
Motor Open Second Brake body
Motor chassis
Trailer
                Composite body

Trailer chassis


3D Printing: The Cabin

I have spent a month or so designing the 3D printed cabin.  It has taken some considerable time to get my workflow correct in Blender, the de-facto free 3D design package (primarily intended for animation); it is arcane and complex but there is a lot of community help out there which makes it ultimately useable. Since Blender is intended for animation it is not so good at helping you to maintain a "manifold" object, i.e. one which 3D printing software can understand and print; a real closed shape, not something with one or two-dimensional protuberances, which can very easily appear when creating complex meshes.  Anyway, here is the finished article and the final print from my Prusa 3D printer, along with many of the test prints.

Cabin in Blender
Cabin printed

The resolution of my printer is only 0.15 mm and you can see this very clearly in the rivets, probably the part of the model which took longest to get right.  I plan to get the final print sent away to be done on a much higher resolution machine.

Rivets in Blender
Rivets printed

Now, while showing this off at work one lunchtime, I was asked why I don't 3D print the rest of the body.  Given what I've learned about 3D printing, and what I don't know about folding aluminium sheet, it is worth considering.  The entire body of one coach works out to be about 600 mm long while my printer maximum vertical dimension (the body would need to be printed vertically to avoid a large support structure) as about 200 mm, and I'd want to stay below that as shapes can become unstable and print a bit "raggedy" as they get higher.  So it would need to be split up into 4 or 5 sections.  This is quite possible since the coach side is split vertically at each door section (see below).  I could use a guttering strip around the top and tape of some form on the roof to hide the rest of the joint.  And the bodies have repeating sections which would reduce the amount of work required.

Door view Body
                permutations

I had a quick go at a test print of the "A" section above and that worked out pretty well. Before I continue, though, I need to work on the chassis so that I can mould-in the connection between the two.

Body test 3D print

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