Gauge 1 Diesel Multiple Unit

This page last updated: 19 January 2020.

First real run of the DMU, at The Dell House in Malvern on 19th January 2020; it is the "express" because there's something strange going on with the speed controller but what the hey, 'tis running:

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, 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 helped me with additional pictures and Chris Moxon of put me 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 me 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 use of bent aluminium sheet 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, for my purposes, 3D printing could 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 to turn out.  But I have to start somewhere.  It is worth pointing out that the project is portrayed below in a linear fashion for ease of reading but was, of course, the usual tangle of iterations and frustrations. Oh, and I didn't build a trailer composite car since my littul railway is so small that there was a danger the DMU might meet itself leaving if I did that.  It is also worth pointing out that this is by no means the only/best approach to the problem of creating a Gauge 1 DMU, and certainly not the only/best approach to 3D printing a Gauge 1 DMU: since I began this project David Leech has printed whole coach sides in one piece with a modified Creality 3D printer; you just have to experiment.

All the Blender/CNC files created during this project can be downloaded from Github. Note that I've chosen to use 1/32 scale to keep things simple, rather than the exact 30.48 factor implied by 10 mm to the foot.


The dimensions of the vehicle are based on the drawings from enhanced by a visit to the Great Central Railway for a detailed photographing/measuring session.  One point of detail to note, which I got wrong first time around: the hinges of a door are always on the left as you face the door, hence the doors on either side open different ways with respect to the direction of travel of the DMU.

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

Trailer chassis

3D Printing: The Cabin

I spent a month or so designing the 3D printed cabin. It took 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 maintaining a "manifold" object, i.e. one which 3D printing software can understand and print; a real closed shape, without 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, all printed in PLA, the default material for 3D printing work (which is long-term biodegradable).

Cabin in Blender
Cabin printed

The "optimal" resolution (balancing print time and quality) 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.

Rivets in Blender
Rivets printed

I tried increasing the resolution: here is the riveted area, photographed under a microscope, at 0.15 mm, 0.10 mm and 0.05 mm resolution, print times increasing from 3 hours to 12 hours:

Rivets at 0.15 mm
Rivets at 0.10 mm
                resolution Rivets at 0.05 mm resolution

0.10 mm layer height seems a sensible compromise. And I need to align those edges along the x-axis to avoid the rastering effect.

Of course, I also need to start 3D printing in my target material, ASA (a UV-safe version of ABS).  I had originally expected to get the final parts printed on a more expensive, higher resolution, 3D printer, so I sent the front section to be printed on a few other 3D printers (all in ASA):
Dremmel print
Printed on my
                printer (in ASA) for comparison
                printed, detail Dremmel print,
My printer
                for comparison, detail

The Fortus 450MC prints are definitely much higher quality, the individual steps being more finely registered.  The Dremel prints have a higher definition around the window area but are otherwise pretty similar to those from my Prusa printer.  But how much all of this matters will depend a lot on how I finish the prints.  The recommended way to remove the "ribbing" of the 3D print is to use sandpaper, which would be really laborious if I'm going to make loads of 3D printed parts, so I thought I'd try my hand at acetone vapour smoothing.  Placing an ASA (or ABS) 3D print in a sealed box containing kitchen-towel soaked in acetone for a few hours effectively melts the surface of the print.  However, you lose definition along the way.  In a test, I found that if I left the print in the acetone long enough to smooth the ribbing (between 3 and 4 hours) then I also lost the detail around the windows and, even if I might prevent that with some form of acetone-resistant coating, the result still wasn't really good enough, too indiscriminate for such a small and detailed print:

Before acetone
After acetone Before acetone,
                rivet detail After acetone,
                rivet detail

Looks like it's loads of sanding for me.  Here's a test piece after 15 minutes of sanding with sanding sticks, one coat of primer, another 15 minutes of sanding and another coat of primer.  Good enough; the secret is to be bold on the coarse grade (80 grit).  It has somewhat lost the rivets, and in the paint rather than the sanding:

Sanded finish

Having satisfied myself that this was the right approach, I started adding detail.  First, I added a slot to the Blender model of the cabin into which I could insert windows (cut from the 0.5 mm plastic sheet used for dolls house windows); these windows aren't going to be pushed out by mistake when handling the model.  They would have to be masked if I were painting post-assembly but I think I will be able to paint the individual sections before assembly and only then insert the windows.

Window slot
Window slot

Then I added the controls...

Dashboard Dashboard

...and some ridges to the cabin and cabin roof so that they would mate together somewhat...

Ridges in cabin
Ridges in cabin
Ridges in action
Assembled cabin

...and finally, since such an intricate object tends to cause the slicing program to add random support structures which become difficult to break away, I manually added just the supports I needed and spent 18 hours printing out the final ASA object in 0.05 mm resolution.  Here it is, on the left just as printing completed and on the right the assembled article awaiting painting; the gap between the roof and the cab front is for a guttering strip which will be added afterwards.  Note that I later switched to printing the roof in black ASA to reduce the need for painting.

Final cabin
                      before finishing Cab completed


I purchased from Tenmille a pair of AG140W bogie kits and from Fosworks a pair of MOT100 nose-hung Fosmotors, powered from 12 V on 30 mm diameter wheels, plus six plain-old MOT310 30 mm diameter wheels; I tried 34 mm wheels originally but the aspect ratio of the whole thing looked wrong and the buffers to adjacent cars ended up being a few millimetres too high.  Assembling the bogie with the un-driven wheels was fairly straightforward.  I filed off the "SR" emblem from the axle covers of the casting and left out the optional step across the middle (which is only relevant to brake vans).

Undriven bogie
The original

To fit the Fosmotors in the other bogie, I first drilled the 2.25 mm holes as directed in the bogie assembly instructions (2.3 mm is fine) then test-assembled the lot without gluing anything but with everything held together as tightly as the final thing would be.  I checked that the wheels ran freely; if not, the 3.2 mm holes in the side-plates may need to be drilled slightly deeper.  With the wheels visually centred between the side-plates, I marked on the bogie centrepiece where the Fosmotor suspension brackets landed.  I disassembled everything and glued the nylon axle bearings into the holes with cyanoacrylate adhesive; I was sparing with the cyanoacrylate adhesive as I didn't want glue collecting in the hole.  I drilled 6 mm holes in either side of the bogie centrepiece where the marks were made, drilling the 6 mm hole in the centre/top at the same time, and again test assembled the lot, easing the Fosmotor suspension brackets into the holes and making sure that the wires come out over the top of the bogie.  I did this a few times, using a needle file to ease-out one of the holes in the bogie centrepiece sides in order to get everything to assemble nice and square; you can see the shape one of the holes ended up for me in the picture below.

Mark bracket positions Drill holes Eased-out hole
Fosmotorised bogie assembled

I originally tried making the steps up to the cab with folded aluminium (you'll see these in some of the videos below) but they stuck out too much so instead I 3D printed them in black ASA. The steps were adjusted as necessary with a sharp knife, ensuring that the portion which hooked-over inside the bogie did not foul the wheels, and glued into place with cyanoacrylate adhesive.  I found later that if I rolled the model on a surface while handling it these steps had a tendency to hit the surface and break; easily repaired with a spot of cyanoacrylate adhesive but still irritating.  It might be worth reinforcing the uprights somehow or maybe printing these in something like Flexible PLA so that they bend instead of snapping.

Steps glued into position


I decided to CNC cut the base of the chassis on my High-Z/S-400T CNC milling machine from  I began by making a few drawings including castellations that represent the wooden steps up to the doors.

                open second base
Motor open second brake base Trailer
                composite base

Note: the bogie attachment holes are 6 mm and are drilled beforehand in a stand drill so that I could then use the same holes to bolt the plate to the milling machine while it is being cut (and in fact I had to make an additional 6 mm hole in the centre of the plate for that purpose as well, which came in handy later for electrical wiring).  I also added two slots to accommodate a strap to hold the battery in place within the chassis of the motor open second.  Here's a preview of the motor open second base, drawn in VCarve, the software which happens to come with my milling machine, and the resulting work.

                  plate preview Milling in
The milled result

I cut the first version in SWG 10 brass plate (3.2 mm thick, which just about scale-matches the 110 mm depth of the upper part of the visible chassis frame), thinking that I could then braze a length of brass bar to each end to which I could attach buffers etc.  However, this was far too heavy (over 1 kg) so I re-cut it in the 3 mm thick aluminium plate you see above (weighing less than 400 gm) and will attach a bar to the end by some other means.  The spindle was run at 14000 RPM and I used 2 mm and 4 mm Only One PM60 end-mills from Cutwel.  A sacrificial strip of 3 mm MDF was placed underneath the job so that the tools could cut through.

The bogies were mounted on the chassis using 40 mm long M6 cheese-head hex bolts.  I started out using one nut (5 mm high) and a washer then the bogie itself followed by a nice large washer and a lock-nut.  The drawings suggested that the buffer centre should be 180ish mm below the top of the chassis plate, 6 mm when scaled, leaving 7 mm clearance between the tops of the wheels and the chassis base. However, to avoid fouling the buffer bars and lining up the buffers with those of another Gauge 1 vehicle I found that 8 mm was the right choice and so added another couple of washers, leading to the clearances shown below.

Buffer height

I didn't have a speed controller at this point so I just wired the motors directly to a 7.2 V battery pack I had lying around and made a circle of Peco G45 track to see how it would go.  It certainly went; click on the link below to see how and refresh this page if no YouTube video image appears below this text, sometimes it doesn't load on the first attempt.

Having made the main part of the chassis, I spent some time creating and 3D printing the undercarriage, which included a box to house the electronics and some very intricate chassis sides.  Since these were too long for my 3D printer to print in one go, I made them in several parts and created a jigsaw pattern (with 0.2 mm clearance left between the jigsaw edges) to knit them together.

Jigsaw pattern

The key with the intricate chassis sides, even with a high resolution print, was careful finishing: I purchased what became a really indispensable Herzo hand-held rechargeable grinding tool and used it to roughen-out the ridge marks left on the top surfaces of the black ASA by the 3D printing process.  You can see this in the "before and after" picture below where the top part is not yet finished: it has obvious 3D printing horizontal surface zig-zags and stepping, while the lower part has been finished, taking about 15 minutes with the Herzo, mostly on its lowest speed.

One side finished, one not, with the Herzo hand-held
        grinding tool

Here are all four pieces of the sides of the motor chassis finished and arranged in the right order:

Chassis sides (in four parts)

After using the Herzo with a pointy bit to clean up the jigsaw edges I was able to carefully squidge the lot together using a wooden-jawed vice, no glue required.

Jigsaw edge of chassis side
Chassis sides assembly
Jigsaws joined Chassis sides assembled

For the means of attaching the 3D printed parts to the aluminium chassis base, see the body section below.  Here's a comparison with the real thing; good enough for me.

Motor Open Second, right
                hand side.
Motor Open Second, right
                hand side, original

Getting there.

Chassis frame with
                  sides fitted Getting there
Getting there

After some experimentation I decide that the buffer bars were best 3D printed; that way I could incorporate into them all of the necessary retainers/aligners for the buffers and the couplers.  The umbilicals were made from two 35 mm lengths of 3 mm diameter heat shrinkable tubing, the kind of stuff you would use to hold wiring neatly in electronics, and some lengths of 3 mm diameter coiled compression spring purchased off Ebay from  The spring was "screwed" inside the heat shrinkable sleeving and then, with the tube held around a suitably sized former (e.g. a plastic bottle top), heat was applied with a hair drier.  The buffers and couplings were purchased from Tenmille: BR MK1 brass buffers AG312 and screw coupling kit AG257.  They are shown here loosely assembled.

Heat shrinkable sleeving and
Heat applied
Buffer bar assembled

However, that gave me oval buffers not round ones, so Tenmille found me some BR MK1 buffers with round heads, steel this time, which required a little modification: the existing (BA?) thread on the buffer stem was re-cut and extended with an M3 die to 12 mm long from the original 6 mm.  An M3 nut was tightened on this new thread once the buffer was inserted into the brass mount and the buffer bar; the nut served to secure the buffer and provide a surface for the spring to push against. As you can see, I also added two 4 mm holes (with nut-traps on the underside) to fix the buffer bar to the aluminium chassis plate using two 10 mm long M4 countersunk head bolts; these won't obstruct the mounting of the body given the corresponding counter-sinking of the holes in the aluminium plate.

Modified round buffer stems Buffer bar fitted

Just to be sure, I made a segment of track of the worst possible radius for my front garden railway (i.e. 1 metre) and checked that the coupling worked under those conditions.

Buffers operating on 1 metre radius curve


For the electronics I went with a Fosworks rig, built by them to order and including the wonderful Legomanbiffo sound.  The sounds are loaded onto a DCC chip and hence I needed a transceiver that spoke DCC, which made for a lot of small boards and required 12 V power.  The boards all fit into the box in the 3D printed undercarriage design.  Of course, I could probably have made more of an effort myself and put together the system more cheaply but, aside from a pause to charge the battery, this professionally pre-wired rig literally worked out of the box, which was very pleasing indeed.

The electronics

By arrangement with Steve at Fosworks the patch board allowed for connection of forward and rearward lights, two aux outputs that were able to drive cab lights at either end, again direction sensitive, and a further aux output which I used to control the internal carriage lights. Here it all is stuffed into the chassis box with an added 0.1 inch pitch connector strip, just visible inside the box, from which all of the electronics inside the body will be fed, cables entering the box through the hole in the middle of the chassis base drilled out to 21 mm diameter.

Electronics inna box

Click on the link below to see/hear a control/sound test; refresh this page if no YouTube video image appears below this text, sometimes it doesn't load on the first attempt.

I used a patch-board to prototype connection of all the 3 mm diameter LEDs so that I could tune the resistor values to achieve the correct brightness.

Patch-board in use to chose resistor values

Using high-brightness white LEDs that needed only around 4 mA to dazzle me, plus boring ordinary red LEDs, the resistor values came out as follows:

Circuit diagram

Measuring the current at various points in the circuit gave the following numbers (with the battery fully charged at nearly 15 Volts):
Given the LokSound decoder is rated at 1.5 A it was barely getting warm.

In terms of the wiring itself, it was planned such that opening the chassis undercarriage box from below and unplugging the cable from the 0.1 inch pitch connector strip should allow the body to separate from the chassis; all of the rest of the cables forming part of the body.  The 8-way cable that connects to the control electronics in the chassis box runs forward along the floor of the motor open second to a connector in the front cab where it splits: to the speaker, to the various lights in that unit and to a 5-way cable which runs back down the floor of the unit to a 5-way radial in-line connector between the two units.  In the motor open second brake the cable runs along the floor to the rear-facing cab where it splits to the various lights in that unit.  Having these "junction boxes" in the cabs means that there is the potential for them to be accessible if the cab roofs can be made removable.  Series resistors for the LEDs were mounted in-line with the LEDs, protected by appropriate heat-shrinkable sleeving.


The colour coding used by Fosworks, which I maintained throughout, was as follows:

Forwards lights
Rearwards lights
Front cabin lights (aux 1)
dark green
Rear cabin lights (aux 2)
Passenger lights (aux 4)
light green
Speaker red
Speaker black
Common (+ve)

To aid with fixing things in position I 3D printed a holder for the SND-620 speaker which fitted the contour of the underside of the roof, the speaker being bolted into it, and I also 3D printed a load of tiny lamp holders into which an LED can be inserted that can then be glued to a surface.  I made a mark on the side of the lamp holder where the cathode of the LED exited (the shorter lead) so that I would know which end was which and I painted the bowl of the lamp holder gloss white (Humbrol 22) for extra reflectiveness.

Holder for SND-620 speaker
Light fitting


While showing the 3D printed cabin off at work one lunchtime I was asked why I wasn't planning to 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 was worth considering. The entire body of one coach was about 600 mm long while my printer maximum vertical dimension (the body would need to be printed vertically to avoid a large support structure) was about 200 mm, and I'd want to stay well below that as shapes can become unstable and print a bit "raggedy" as they get higher. So each coach would need to be split up into 4 or 5 sections. This was 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 covering material 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 design work required.

Door view Body

I had a quick go at a test print of the "A" section above and that worked out pretty well, see below.  The remaining question was that of access. I wanted to be able to get into the body for maintenance but I also wanted it to be rigid and firmly attached to the aluminium base of the chassis.  In the end I decided to add a rim around the bottom edge with the slightest of clips to attach the body to the aluminium base.  At two points I added cross-pieces to accommodate M6 bolts that will hold the chassis detail in place, traps being made in the cross-pieces to hold the nuts so that the bolts can come up from below; hence the bolts anchor the body to the aluminium base as well as the chassis detail.  The ASA-printed traps had a slight tendency to crack when inserting the nuts but this was nothing a little cyanoacrylate adhesive couldn't fix.  The required holes in the aluminium and the chassis 3D printed parts will be drilled only once the body is assembled to allow for alignment slop.  Note, also, the slots in the Blender image of the body sides for windows to be inserted.

Body test 3D print Closed loop body Trapped nuts

It took several weeks each to design/test-print the body sections before final printing in natural ASA at 0.15 mm resolution.  I abraded the outside of each section pretty vigorously with grit 80 on an abrading stick, while trying to avoid removing features, the aim being to git rid of the "3D printed" look.

Body section
                            D abraded Body section D in

Before I could complete printing the body I needed to figure out how the corridor joiners should work.  I tried 3D printing one out of Flexible PLA which is really flexible and looks good but, despite being as thin as I could make without causing the printer to leave holes in the shape, the square nature of the structure meant that it wasn't concertina-style side-to-side flexible as I needed it to be.

Flexible PLA corridor

However, at this point I had completed all of the 3D printable parts in Blender and, while up to now I had simply been using Blender as a means of creating printable shapes, it occurred to me that I could put all of the parts together, colour them and create a properly animated/rendered video tour.  Here it is; refresh this page if no YouTube video image appears below this text, sometimes it doesn't load on the first attempt.

But back to the corridor joiner; I turned to latex.  I tried 3D printing a mould from PLA and ribs from black ASA, then painting black latex on the inside of the mould, inserting the ribs, painting more latex etc., building up a few layers.  That was messy and still not flexible enough.  However, during a lunchtime conversation at work the subject of origami came up and John subsequently brought in his copy of Steve and Megumi Biddle's The New Origami plus a test folding of their "Troublewit" design, a concertina-shaped thingy which looked pretty much perfect aside from the scale.  After satisfying myself that this could be painted with black latex (much easier than painting the inside of a mould) I set to scaling it down.  Find below the resulting pattern.

Corridor Joiner

The origami corridor joiner was created as follows:

  1. Print two copies of the image 1:1 (i.e. don't let the printer driver scale it) and check that the dimensions of the printed edges are actually as indicated in red.
Checking printed size
  1. Take one of the print-outs and, using a sharpish edge (e.g. the point of a kitchen knife the wrong way around) against a steel rule, score along all of the vertical lines (the faintly blue lines) and then cut out the wanted rectangle of paper with a sharp pair of scissors.
Scoring vertical lines
  1. Turn the paper printed-side down and fold the top edge at the upper bold black line (i.e. the one marked as being 30 mm in); this fold was made as accurately as possible.
First fold
  1. Fold the same edge back up again so that it meets the less bold black line (the one beside the 30 mm one).
Second fold
  1. Repeat steps 3 and 4 with the lower edge, folding it up and then back down again.
Major folds completed
  1. Take the paper in both hands and fold it alternately up and down at the scored edges to form a concertina shape.
Folding the concertina The concertina folded
  1. Here's the tricky bit: pull out the start of the upper edge that was folded down in step 3 and, allowing the concertina to expand so that the paper doesn't rip, work along using a thumbnail to gently push each peak of the concertina inwards so that the concertina can be compressed once more with the folded-out side at 90 degrees: the paper will want to do this, the thumbnail is helping it; if the folded-out part is not quite at 90 degrees, continue to adjust the peaks until it is.
Pulling out fold Pushing
                in peaks with thumbnail Fold
                out completed Right
  1. Repeat for the lower edge that was folded in step 5.
Both corners completed
  1. Repeat steps 2 to 8 for the other sheet of paper that was printed-out in step 1 and then meld the two half-corridors together, tacking them to each other with a tiny amount of PVA in a few spots just to stop them falling apart (making sure that the glue doesn't get in the way of the concertina action); it doesn't matter if the inside is a little wonky, it is the outside that needs to be nice and square.

A pair of end plates were then printed in black ASA and three self adhesive 20 x 6 x 1.5 mm neodymium magnets were glued to each of them (I scraped off the weak glue layer provided on each magnet and used cyanoacrylate adhesive), one on either side towards the bottom and one at the top.  The magnet-sides of these end-plates where then glued to the paper very carefully with cyanoacrylate adhesive.  Finally the lot was stretched out slightly and painted with three coats of black latex, allowing several hours drying time between each coat.  Neodymium magnets of the same dimensions and opposite polarity (i.e. with the weak adhesive on the other side) were fixed around the inside of the door openings on each coach, giving me an easy magnetic fix, shown below in a test fitting.

End plates
End plates glued to
Joiner test fitted
Corridor joiner test

Strong, waterproof and flexible; refresh this page if no YouTube video image appears below this text, sometimes it doesn't load on the first attempt.


Internal Features

The internal features comprised the seating and partitions; I decided not to attempt any form of luggage rack as it would not be visible from the outside in any case.  The seats were 3D printed in natural ASA at 0.10 mm resolution which, handily, needed no finishing aside from a quick rough filing of the horizontal seat surface; the ribs of the 3D printing matched the ribbing of the real seat fabric.  Mounting ridges for the partitions were built into the 3D prints of the body sections.  The partitions were printed in pairs, one glued either side of each ridge, to achieve the correct thickness.

Seats Partition

As well as the seats shown above a few variations were made to accommodate fitting around various obstructions and gluing to different surfaces.

Seating plan

The seating plan amounted to:

Painting And Decorating

I began my first painting experiments with the difficult part: the body, the sides of which I painted separately before assembly.  First I abraded the surface but did not take the time to make it perfect, just removing the 3D printed look, as the first photograph below shows.  Then I cut a couple of 30 mm wide strips of paper and inserted these in the window slots, adding some masking tape inside to ensure no gaps along the top of the slot, and masked the roof and both ends off with masking tape and paper.  Placing the body section in my littul portable Nielsen spray booth I applied two coats of Halfords (i.e. automotive) white acrylic primer from a spray can, leaving 15 minutes between coats.  I later bought a second Nielsen spray booth since they can be placed side by side with the central barrier removed, allowing sufficient room for all the sections of one DMU unit to be sprayed in one go, ensuring a consistent finish.

The finish before
                painting began
Primer applied
After priming

Now that I could really see the imperfections properly (I'll be more careful on that first abrading in future) I started again with the rubbing down, this time using my Herzo on its lowest speed setting to get into the trickier parts and finishing with a grit 400 sanding stick before applying another coat of primer and rubbing that down.  Good enough; I will improve my technique as I progress with the work, going through the sequence of 80 (plenty of this), 180, 320 and then 400 grit abrading sticks, no shortcuts; you just end up doing the stages later anyway.

Another rub-down
Primed again
Rubbed down again

I left this to harden thoroughly for 24 hours; perceived wisdom on the web is that it is OK to apply enamel paint on acrylic primer provided the primer is left to stabilize properly first.

For the final coat on the body sides I first tried using two coats of Railmatch paints RM207 BR Rail Blue (satin), thinned with an equal quantity of enamel thinners and applied with an airbrush.  This was the first time I'd used an airbrush and I learned two things: (a) it is very easy to over-thin the paint and achieve a runny result (for Railmatch paints add an equal quantity of thinners at most) and (b) one 15 ml jar of RM207 BR Rail Blue is barely enough to spray a single body section.  Later I moved on to using Phoenix Precision Paints P132 BR Rail Blue (Dull) which was available in larger quantities, also spray cans, and should be thinned even less (80% paint to 20% of their PQ9 Quick Air Drying Thinners).  Anyway, I persevered with two test sections, inserted windows and joined the sections with cyanoacrylate adhesive.  The finish was not bad and the join was not visible on the sides.

Painted body
                    segments Body final finish
Join, side view

Much later when I did the painting for real I arranged it such that the painted side was horizontal so that a generous coat of paint could be applied without running and I rotated the coach by 180 degrees between applications to ensure coverage.  My little Badger 250 airbrush took just about enough paint for one coat on one side so, leaving 24 hours between coats and applying two coats, painting was a slow yet satisfying process.  Two 125 ml tins of blue paint were required for my two-coach DMU.

Paint and thinners (not
                    mixed) before spraying.
First coat applied.

I did experiment with inserting the "glass" first and using something called Humbrol Maskol, which I believe is just somewhat thinned latex, to mask the windows before spraying.  This worked pretty well, though spraying before the "glass" was inserted still gave a cleaner finish:


That left the roof.  First I tried applying the same black latex as I used for the corridor joiner with a brush but the finish was awful.  Then I purchase some matt black polyester Solarfilm, the material one uses on model planes, but it proved impossible to apply neatly to a solid plastic surface; no matter what I did (heating and stretching it with the proper tools, applying additional adhesive in various ways) air bubbles always reappeared underneath the film after it was left to stand for a few hours.

Finally I turned to 0.5 mm thick styrene, purchased in large sheets (660 mm x 1370 mm) from 4D Model Shop.  I 3D printed a former the exact size of the roof out of polycarbonate, which is heat resistant to around 140 C, then cut the styrene sheet into a strip 106 mm wide and the length of the straight part of the roof (i.e. up to the start of the curved cabin roof section) and fitted it into the former.  Heat was then applied, in my case by placing the lot into a fish kettle and covering with boiling water for 5 minutes with a weight on top to stop it floating; you could also use an oven turned down to 100 C or you could apply heat evenly with a hairdrier.  After test fitting/trimming the roof was sprayed with two coats of grey primer and two coats of matt black acrylic paint (Halfords/automotive again).  The pictures below show the results of a test run.

I later found that the same styrene sheets were available in black and so I was able to skip painting the styrene roof; I printed the cab roof out of black instead of natural ASA but still sprayed it with a couple of coats of automotive matt black paint as abrading the black ASA to a scratch-free finish was prohibitively difficult.

polycarbonate former
Styrene in position Boiled water bath
Styrene after moulding
Test fitting

The outside of the cab front was rubbed down, masked and spray-painted in the same way as the body sides except this time using Phoenix Precision Paints P134 BR Signal Yellow (Dull) from a spray can for the top-coats; two 150 ml cans were required in total. Then the control-panel area inside was painted with a coat of Humbrol 64 enamel matt grey before the controls themselves were picked out in largely gloss colours: black (Humbrol 21), white (Humbrol 22), metallic (Humbrol 56 to pick out parts of the instrument panel and Humbrol 11 for the handles/wheel themselves), red (Humbrol 20) and green (Humbrol 30).

Cab undercoated
Top outer coat and
                undercoated control panel
Control panel

I left painting the chassis sides, drivers' steps and buffer bars until the weathering stage post-assembly.

For the partitions, I just painted a coat of gloss dark brown (Humbrol 10) on the raised areas that represent the woodwork.

                    painted Brake van

The seats were painted in Humbrol enamels: on all surfaces except the one that will be glued a coat of matt grey (Humbrol 64) followed by a coat over what would be the upholstered area of matt dark green (Humbrol 30) and, on top of the green, three narrow double stripes of matt light green (Humbrol 90), two or three thicker stripes of matt mid green (Humbrol 226) and two or three narrow stripes of matt brown (Humbrol 110).

Green coat
Seats original
Seats model

For the door handles I used Tenmille AG207 T handles and AG209BR grab handles (36 off).  These are brass so, to get the right look, I plated them with nickel using the following procedure (based on this article and this video):

In the last row of pictures below the plated handles are shown beneath their un-plated counterparts and then the test-fitted handles (holes in the body made with a 1 mm drill and a blob of thick cyanoacrylate adhesive applied on the inside of the body to hold the handles in place) are shown beside the real thing; somewhat on the chunky side but they will do.

Nickel acetate Cleaning the brass Plating
Handles fitted
Real door

For the long grab-handles fitted beside the driver's door (4 are required) I purchased some brass strip, 0.4 mm x 1.6 mm, from 4D Model Shop, cut pieces 47 mm long and soldered 24 SWG (0.55 mm diameter) wire to either end and the middle for anchor points.  I haven't done so in the test fitting shown below but, from what I could see from the images on, these long handles are generally painted the same colour as the body where they are mounted so there was no need for nickel plating, I will just paint them before final fitting.

The long handles Long handle test fitted

I had no pictures of the long handles by the brake van doors as the ones on the DMU in the Great Central Railway were removed when I visited.  However, from the picture below it was clear that those handles are made of round bar in two sections so I made them out of 0.8 mm brass wire, which will again be painted before final fitting.

Long handles
                beside the brake van doors
Brake van door handles

The remaining decorations were the ventilation "shells" along the top of the roof, for which I used Tenmille AG243 (40 off).  These were attached to the fitted roof cover with a spot of thick cyanoacrylate adhesive through pairs of 3.2 mm holes spaced 55 mm apart and 12 mm either side of the centre of the roof.  A test fitting is shown below beside the real thing; the shells will be painted matt dark grey before they are fitted.

Roof vents test fitting
The real thing (picture used
                with permission)

Oh, and at the last minute I decided to add a tiny pair of windscreen wipers, printed in black ASA, which will be glued to the cab front using Loctite 408, a glue which is purported to vastly reduce the chance of the fogging that one often gets when using cyanoacrylate on perspex.  The last two pictures below show a test fitting, to a test location on the test-painted body from above, where the wiper was placed into position and a large drop of Loctite 408 was allowed to land on the attachment point then, to hide the glue, the surface of the wiper was very carefully painted matt dark grey (Humbrol 32).  Note that though I printed both directions, only the one with the wiper blade to the left is actually required as that seems to be the usual resting position.

windscreen wipers Wiper glued
Wiper painted


And so to final assembly:

  1. The chassis undercarriage and sides were printed (minimum 50 hours of printing time), finished and squished together.
Chassis undercarriage
                and sides assembled
  1. The printed/finished/assembled buffer-bar/buffers/couplers were attached to the aluminium chassis plates.
Buffers added
  1. The final versions of all the body sections where printed (minimum 240 hours printing time) at the appropriate resolution (see Github for detailed instructions) then tested/fettled to ensure a loose join with the aluminium chassis plates and a tight join with each other at the body sides (ignoring any gaps between the roofs); the ASA of sections 5, in particular, had shrunk at the corridor end and hence the "clips" needed some easing to fit easily over the aluminium chassis plate.
Body sections printed
  1. With body sections 1 and 4 fitted to the aluminium chassis plate the positions of the fixing holes were marked, then the body sections were removed and the 6 mm holes were drilled in the aluminium chassis plate. The chassis undercarriage was loosely fitted to the aluminium chassis plate (supported by resting the buffer bars at each end on blocks of wood) and, using a bolt in the central 6 mm hole to keep it still, the positions of the holes were traced on the undercarriage.  The undercarriage was then removed and 6 mm holes were carefully drilled through it too at the trace marks.  15 mm long M6 bolts were pushed up through the undercarriage and the aluminium plate holes then square nuts were test fitted to the bolts in the nut traps of body sections 1, 2 and 4, ensuring the body sides (now all of them fitted) were not pushed apart by the nuts and trimming away any parts of undercarriage that fouled the clips along the base of the body sides when the bolts were tightened.  I spent a long time on this so that I would have to handle the painted end-product as little as possible.  For the powered unit, the central hole in the chassis is used for wiring so I drilled an additional 6 mm hole, about where the two undercarriage halves join, to hold the undercarriage firmly to the aluminium chassis plate, the square nut in this case being held in place on the aluminium plate using cyanoacrylate adhesive.  To allow room for a wide electrical connector I drilled-out the central hole, through both the aluminium and the undercarriage, using a 21 mm diameter hole saw, which just fell within the boundaries of the undercarriage box.
Test attaching the body
                to the chassis21 mm hole for cablingInside the attached
  1. The final versions of the cab fronts and cab roofs were printed (minimum 50 hours printing time) then tested/fettled for fit.
Cab fronts and roofs
  1. Enough units of polycarbonate mould were printed for a complete DMU roof and then, to hold them in place, they were glued in a line to two lengths of scrap aluminium (left over from the milling of the chassis plates) using an epoxy that specifies it can withstand temperatures of 100 C.  Note: I tried cyanoacrylate adhesive, which said it was good to 180 C, and an epoxy that was meant to withstand boiling water but both allowed the aluminium to came away once submerged in boiling water, maybe because the polycarbonate flexes under heat; it didn't matter too much though - the styrene sheet, once fitted into the mould, kept the polycarbonate sections in place.
Polycarbonate formers
                glued together
  1. Two pieces of black 0.5 mm thick styrene sheet 106 mm by 567 mm were cut to form DMU roofs and these were moulded in the polycarbonate moulds under heat then test fitted to the body sections.
Styrene in formerIn the boiling waterTest fitting
  1. The battery was strapped into place using three cable ties with some fabric electrical sleeving pushed over them to ensure the battery was not pinched; use of a nice narrow cable-tie means that there was no fouling of the seats that will be inserted later.
Cable ties and fabric
                sleevingTies in positionBattery in position
  1. The control electronics were positioned in the chassis box and the LokSound unit (with its very delicate wires) and patch-board were fixed into position with sticky pads; the other boards it was sufficient to just wedge into place.
Control electronics
  1. The assembled bogies, powered and unpowered, with their printed/finished driver's steps, were attached to the aluminium chassis plates; before doing so I made a final check that the mounting holes were dead centred on the aluminium chassis plate and corrected with a round file as necessary. I also re-checked the height of the buffers against another item of rolling stock and ensured that nothing fouled the bogies.  I made a short cable terminated in a JST connector to connect to the motors, ensuring it was unable to foul anything, using a mains terminal block cable-tied to the bogie as an intermediate.
Bogies attachedPower to motors
  1. All of the seats, in the types/quantities required by the seating plan, were printed (around 40 hours printing time), finished and painted.  I used a file on the straight-backed seats to remove the splaying from the 3D printing process at the base of the back, making them completely flat for gluing.
Seried ranks of seats
  1. Two pieces of black 0.5 mm thick styrene sheet were cut, one 73 mm x 570 mm (for the motor open second) and one 73 mm x 403 mm (for the motor open second brake) to fit on top of the aluminium chassis plates and between the body sides.  Holes were cut in the sheets for the various fittings, including the battery strap, using a sharp knife.
Stryene sheets cut
  1. The seats with curved backs were glued to the styrene flooring sheets according to the seating plan using plastic weld, test-fitted body sections being employed as necessary to achieve correct alignment and ensure no fouling.
Seats glued to stryene
  1. The internal partitions were printed, painted and test fitted.
Partitions printed,
                finished and painted
  1. The seats with flat backs were glued to the partitions according to the seating plan using plastic weld, test-fitting the body as necessary to ensure no fouling.
Seats glued to
  1. The cab fronts and cab roofs were very carefully finished (again, a test window fitted and removed) then painted (including the control panels).  The underside of the cab roofs were painted with a metallic paint (Humbrol 11) in order to reflect the internal cab lighting.
Ready to rub downRubbed downPaintedCab roofs paintedReflective paint on iunderside of cab roof
  1. The wiring, including all the LEDs with their in-line series resistors insulated with 1.5 mm heat-shrinkable sleeving, the 5-way inter-coach connector and the junction boxes in the cabs, were made and test fitted/powered, the main cable inside a 5 mm diameter expandable PET sheath.  I took particular care to get the passenger lights into good positions, not fouling the partitions or the speaker.
5-way connector18 way 0.1" pitch
                connector block in front cabin8-way 0.1" pitch connector block in rear
Wiring looms for lights
  1. The forward and rearward headlights, forward lights on top, were glued into position in the cabs with cyanoacrylate adhesive.
Wiring sideLights side
  1. The sides of the body sections were carefully finished, a test window fitted and removed from each, then masked and painted; the roof will be covered with styrene sheet and so required no finishing. Note: any hinge or door stop that had been accidentally shaved off was reinstated before painting with a tiny piece of ASA scrap, glued into place with a generous amount of plastic weld and then shaped with my Herzo.  The outside of the "clips" and the cross-struts inside the body were painted matt dark grey (Humbrol 32) to help them disappear.

    This step took by far the longest time, probably around a month of evenings including time off for good behaviour
                        painting underway. Final coat
All painted
  1. "Glass" was added to the body sections and cab fronts, each strip 30 mm wide for the body sections and 35 mm wide (subsequently trimmed with a scalpel) for the cab fronts.
Body with glassCab fronts with glass
  1. After clearing any overspray off the edges with my Herzo, the body sections and cab fronts (but not cab roofs) were glued to each other with cyanoacrylate adhesive and, afterwards, any visible plastic was touched up.
  1. The long handles were painted as required to match their locations.
Long handles paintedReady for mounting
  1. All handles, long and short, were fitted and glued into position with a blob of thick cyanoacrylate adhesive and touching up any visible plastic around the drilled holes with some paint on the end of a cocktail stick.

    WARNING: when applying cyanoacrylate to the rear of the door handles in particular, fogging may result on the nearby window panes.  This can be largely removed with rubbing alcohol on the end of a cotton bud.  Since I was modelling a train with single-glazed windows returning full of people from their Cardiff shopping trips on a damp Saturday afternoon, the remaining fogging was merely scale-accurate condensation for me but if it is undesirable consider using Loctite 408, blowing air through the carriage while gluing or masking the inside of the nearby windows with Humbrol Maskol.
Handles, left hand
                sideHandles, right hand
                sideBrake van handles
  1. For the guttering strip running along the sides and around the front of each carriage I was originally intending to use 1 mm square-section brass wire but it proved very difficult to get kink-free so, at the last minute, I changed my mind and purchased three 1 metre strips of 1.5 mm square-section ASA from 4D Model Shop, used the heat of a hair drier to allow me to bend it appropriately, carefully glued it into place along the sides with cyanoacrylate adhesive and then equally carefully applied a couple of coats of paint to match the body in each area.
Bending ASA stripPositioning guttering
                around cabGuttering strip glued
                and painted
  1. The moulded black styrene roofs were glued into position.  Plastic weld alone didn't work as it did during testing, possibly because there was now paint around the edges of the roof above the guttering, getting in the way of the weld.  Instead I applied a generous quantity of plastic weld on the centre of both roof surfaces (where there was no paint), positioned the roof so that it fell within the guttering, ensuring that the cab roof could still be clipped into position and removed, then weighed-down the roof to affix it.  Then I turned the carriage over and applied cyanoacrylate adhesive at the edges, working my way along and holding until fixed.  Afterwards the guttering needed touching up again.
Roof weighed downCyanoacrylate around
                the edgesRoof gluedRoof glued. rear view
  1. The ventilation shell tops were painted matt dark grey (Humbrol 32), leaving the lower portion unpainted in order that they can be glued into the roof. While I had matt dark grey paint handy I also painted the exposed ASA where the main roof joins the cab roof to stop it shining through the crack between the two.
Ventilation shells
  1. Holes were drilled in the roofs for the ventilation shells and these were glued into position with thick cyanoacrylate adhesive, applying just a small amount of glue to the stem to tack them in place and then turning the carriage over and applying a further blob of glue into the hole.  The shells were arranged such that their line of symmetry ran along the length of the carriage. Once mounted they were given another coat of paint.
Ventilation shells
                fittedGetting close now
  1. All of the remaining electronics bar the cab lights were fitted: the passenger lights and the speaker in its holder secured with cyanoacrylate adhesive, the "junction boxes" secured with Araldite standard; the wiring was arranged such that it was as invisible as possible when viewed from the outside.  Since there was very little space I plugged the cab lights in as well at this point, even though they won't be glued into position just yet.
Passenger lights and
                speaker gluedJunction box, frontJunction box, rear
  1. The two main internal partitions were fitted next: grooves were filed in them to accommodate the passage of the electrical wiring and then the partitions where glued into position, cyanoacrylate adhesive being applied at the roof and the base, the sides left unglued to ensure no fogging of the nearby windows.
Partitions fitted
  1. With the cab lights plugged in, the cab partitions/walls were filed/fitted/glued into position behind them.  The cables of the cab lights were then glued to the cab partition walls, arranging them such that the cables/lights did not foul the cab roof when it was clipped into position and again care was taken to avoid fogging of the windows due to the cyanoacrylate adhesive.
Rear cab partition
                fittedRear cab lights
                fittedTop view of front cabFront cab, front view
                of wiring
  1. The magnets that attach the corridor joiners were glued into position inside the section 5 bodies (existing weak glue scraped off and replaced with cyanoacrylate adhesive) and then the final two seats with straight backs were glued into position in the back of the motor open second with cyanoacrylate adhesive.
Magnets fitted in
                motor open second brakeMagnets and rear seats fitted in motor open secondCorridor joiner
                between coupled carriages
  1. Following a test fitting of the bodies to the chassis plates the long internal cables were tacked to the body's cross-pieces/partitions here and there with cyanoacrylate adhesive in an attempt to keep them at floor level.
Tacking points
  1. The windscreen-wipers were attached to the cab fronts using Loctite 408 with a hair drier blowing air away from the "glass" over the joint to make really sure there was no fogging, then the top surface of the wipers was carefully painted matt dark grey (Humbrol 32) to hide the glue.
Windscreen wipers
                attached and painted
  1. The visible parts of the bogies and the visible sides of the aluminium chassis plates, in particular the sticky-out step bits, were painted matt dark grey (Humbrol 32).
Bogies and visible
                chassis plate painted
  1. After using some rubbing alcohol to clean all of the windows of any fingerprints etc., no smoking signs (Fox Transfers FRH10019/3) were applied to the inside of the windows according to the markings section below.  Moving each transfer on the end of a toothpick, I arranged the lines on the tea-towel I was resting the body on to make initial alignment as easy as possible before turning the model the right way up to make final adjustments to the position of the transfer while looking at it from the outside.
Window decal positionedMore no smoking signs
  1. The assembled bodies and styrene sheets holding the seats were finally bolted onto the aluminium chassis plates.
Bodies attached to


After consulting Noel on the Welsh Railways Research Circle forum, studying a very long thread on the Class 116 by ChrisF on RMWeb and with the help of Robert Masterman and others on the "Railways In South Wales" Facebook group, I determined that the markings on the DMU should be as follows:


Basically the BR logo goes under the window nearest the cab, "Private" goes on the driver's door, "Guard" on the guard's door, the 5 digit ID number (these chosen from page 17 of ChrisF's thread to be C334 coupled to C301) with a regional prefix of W for Western Region goes under the right-most window and the "no smoking" compartments I judged from this picture and this picture.  No lettering on the cab front (e.g. "C334") was applied during the all-BR-blue livery days.  One of my pictures from the Great Central Railway shows a spec plate on the rear left hand side, for which I used Fox Transfers F10360.

Right hand
                side 1
Right hand
                side 2
Left hand side
                1 Left hand side

On the destination boards I chose to apply, with some poetic license, "RHYMNEY" at one end and "CARDIFF" at the other. For these I used Fox Transfers Gill Light (FG1000) 3 mm high, applied to the 3D printed inserts that fitted into the destination display, then the inserts were pushed into their mounting holes.  All of the transfers were given a coat of Phoenix Precision Paints PV72 Satin Varnish to protect them from finger damage.



Finalising consisted of finishing the painting of the chassis and adding weathering as appropriate to the entire model, often useful to hide its imperfections.

All of the features of the 3D printed chassis were painted some colour or other in order to make them stand out from the supporting structure.  The Humbrol colours I used are indicated in the pictures below.

Chassis paint
            left hand side
Chassis paint
          right hand side

Where Humbrol 29 was used apart from on the exhaust pipes it was dry-brushed to give a rust-like effect. Where Humbrol 19+10 is shown this was a coat of Humbrol 19 followed immediately (i.e. without waiting for it to dry) by a coat of Humbrol 10 to achieve a reddish brown.  "As cab" indicates P134 BR Signal Yellow (Dull) from Phoenix Precision Paints.  The steps up to the cab, the buffer bars and the connectors between the coaches required no painting.

To add weathering I dry-brushed Humbrol Dark Grey Wash over most of the painted surfaces apart from the yellow area (which I felt needed to be garish), particularly addressing the light grey parts, applied Humbrol Rust Wash to the springs of the bogies and Vallejo Rust Texture to all of the exhaust pipes.  Where surfaces that weren't meant to be shiny showed some glossiness this was subdued with a coat of the very matt indeed Vallejo Matt Varnish.

Left hand side
        with weathering
Right hand
        side with weathering

For comparison here's a left-hand side view of the real thing, not in service and hence probably more on the grungy-side, from our photographs at the Great Central Railway:

The real thing

The other areas which I thought needed attention were the roof and the rear of each coach.  The ventilation shells I gave a very light dry-brushing of Humbrol Rust Wash, any areas of glue overspill on the roof were painted either the same or with dark green Humbrol 30 to represent mildew and one particularly bad spot of cyanoacrylate overspill was covered with a small patch of matt black insulation tape edged with spots of gloss black Humbrol 10 applied with the head of a pin to represent rivets and Humbrol Rust Wash around the side, all intended to represent a repair job.  On the rear of each coach I dry-brushed Humbrol Dark Grey Wash to represent the marks left by water run-off from the guttering.

Roof repair job
Coach end

And with all of that done, here's a "live" tour to go with the 3D modelled tour, though obviously only around the outside.  Refresh this page if no YouTube video image appears below this text, sometimes it doesn't load on the first attempt.
The video at the top of the page is of the first real run of the DMU, at The Dell House in Malvern on 19th January 2020.

Lessons Learned

The things I learned from doing this project included:


In the interests of getting my life back, this model omits the following features:

  • the two large ugly digits between the headlights on the front of the cab: if less poetic license is allowed these should be present however they make the DMU so ugly I chose to leave them off and stick with a C334-style cab but in the all-BR-blue livery,
  • the lamp hooks above each buffer: though I had the materials to make them they were just too fiddly and likely to break for me to fit them,
  • luggage racks: wouldn't be visible so no point,
  • vertical pipework on the body ends: too fiddly again,
  • the actual brake inside the brake car: wouldn't be visible so no point,
  • people: I ordered some painted seated figures from Hong Kong but the smallest man was 6' 4" tall and all the figures sat with their elbows sticking out so I had great difficulty fitting them sensibly onto the seats.

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