Gauge 1 Diesel Multiple Unit

This page last updated: 26 June 2019.

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 go 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.

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 suggested 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 a dashboard...

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 later.  Note that I later switched to printing the roof in black ASA as then there was no need to paint it.

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 required for 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 will 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, didn't want it 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 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.

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 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 for the motor open second portion of the DMU.

                  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 way 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 used one nut (5 mm high) and a washer then the bogie itself followed by a nice large washer and a lock-nut.  The drawings suggest 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, usually on its lowest speed setting.

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 placed in the right order:

Chassis sides (in four parts)

After making sure that the jigsaw edges were nice and clean 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 experimenting 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 2.5 mm diameter heat shrinkable tubing, the kind of stuff you would use to hold wiring neatly in electronics, and some lengths of 2 mm diameter coiled spring purchased off Ebay.  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 extended with an M3 die to 12 mm long from the original 6 mm and an M3 nut was tightened on it once the buffer was inserted into the brass mount and the buffer bar; this 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 counter-sunk 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 a box that is part of 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 towards the left of 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 (which, during assembly, I drilled out to 21 mm in diameter to allow a nice wide connector through).

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 current/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 a 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 formed 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 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:

Forward lights
Rearward 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 also 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 exitted (the shorter lead) so that I would know which end attached to the series resistor 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 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) is 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 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 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 and, by default, for the body to form a closed loop, i.e. including a floor.  This floor is actually only maintained around two sets of holes for more M6 bolts that will hold the chassis detail in place; the remaining portions of the body floor will be cut away (in the Blender model) to allow access.  I created traps in the floor to hold the nuts so that the bolts can come up from below; hence the bolts anchor the body to the 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 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 avoiding removing features, the aim being to remove 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 (from 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.  The image below was the result.

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 copies 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, 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 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 to which the 3D-printed partitions were glued.  The mid-body partitions were printed in pairs, one glued either side of the 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 further 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 (25% 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

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. 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, for each seat 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 and brake van door (6 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

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 black 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 and windows 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 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 matte black (Humbrol 32).

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 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 connector I drilled-out the centre hole, through both the aluminium and the undercarriage, using a 21 mm diameter hole saw, which just came 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. 1 mm square-section brass wire (purchased from Ebay) was cut to size for a guttering strip and test fitted to the body/cabs as test assembled, secured by bending it back into 1 mm holes drilled in the corridor ends; it didn't need to be dead straight as it will be glued into place later, just the right size and relatively kinkless.
Guttering strip bent
                roughly to shape
  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 fittingTest 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 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).
Ready to rub downRubbed downPaintedCab roofs painted
  1. The wiring, including all the LEDs with their series resistors, the 5-way inter-coach connector and the junction boxes in the cabs, was made and test fitted, channels being made as appropriate in the partitions to let the cables (sheathed in 5 mm flexible PET) through.
[from here on still a work in progress]
  1. The sides of the body sections were carefully finished, a test window fitted and removed from each, then 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 matte black (Humbrol 32) to make them disappear.

  1. "Glass" was added to the body sections and cab fronts.

  1. The body sections and cab fronts (but not cab roofs) were placed into position on the aluminium chassis plates (without the styrene sheets holding the seats) and glued to each other with cyanoacrylate adhesive, being careful not to accidentally glue them to the aluminium chassis plate.

  1. The long handles were painted as required to match their locations.

  1. All handles, long and short, were fitted and glued into position.

  1. The internal partitions were glued into position.

  1. The assembled body sections were fitted to the aluminium chassis plates and the painted roofs glued into position on top with a generous quantity of plastic weld, ensuring that the cab roofs could still be clipped into position and removed again afterwards.

  1. The brass guttering strip was fitted into position, glued with thick cyanoacrylate adhesive wherever necessary to keep it neatly in position and carefully painted to match the sides of the body sections.

  1. The ventilation shell tops were painted matt black (leaving the lower portion unpainted in order that it can be glued into the roof).

  1. Holes were drilled in the roofs for the ventilation shells and these were glued into position with thick cyanoacrylate adhesive.

  1. The magnets that attach the corridor joiners were glued into position inside the section 5 bodies and then the final two seats with straight backs were glued into position in the back of the motor open second.

  1. The assembled bodies and styrene sheets holding the seats were finally mounted on the aluminium chassis plates.

  1. The windscreen-wipers were attached to the cab fronts using Loctite 408 with a hair drier running, on cold, blowing over the joint to make really sure there was no fogging.

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:

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