From start to finish it took 11 years to complete
This is Part 1 of the Didcot: A model steam locomotive on 5" gauge (1:11.3 scale) of the Great Western
Railway 0-4-2 14xx class.
1 Part 2
Extra part 4a
The real loco 1420
and train at Riverford Bridge (England). This is one of the few survivors of
Western Railway 14xx class 0-4-2 tank locomotives (1420, 1442,1450, 1466
are preserved). Introduced by C.B. Collet in 1932 to replace the ageing 517
class tanks, of which the 14xx were updated versions. They were originally
numbered in the 48xx series and were fitted for working auto trains. Mainly
for use on branch lines, they were also capable of a fair turn of speed. I
chose this locomotive for my next project because I saw it in a movie "The
Titfield Tunderbold" and liked the appearance of these tiny engines. I
started out with the 7 1/4" gauge version 'Dart', designed by Martin Evans
and serialised in ME, but I found it was too big to handle and to make with
my workshop equipment. So I ordered the catalogue of Reeves (England) and
found there was also a 5" gauge version.
I started with the model locomotive in January 1996, after buying the
(RV 70 'Didcot')
and the wheel castings from Reeves. The design for 5" gauge is from H.N.
Evans, and although the copy isn't very good (sometimes hard to read), the
drawing is fairly good, with lots of general detail. With the aid of a set
of original Swindon work drawings, I should be able to make a close copy of
the real thing in the 1" scale.
casting of one of the driver/coupled wheels as they came from
Reeves (England). Posting and packing costs are very expensive, so I try to
minimise the use of castings. Alas the bosses are to big (according to the
prototype), but that is hard to alter now. The cast iron of the wheels is of
a good quality and easy to machine.
horn blocks in the
frames. My old (1948) American Van Norman no.6 milling machine is put to use
for milling the horn block castings. The blocks are riveted in the frames
with 2 mm steel rivets. Not original GWR, but very sturdy. To prevent oil
from getting between the horn blocks and the frame (which is very
inconvenient during painting) the horns were first fixed with glue (Loctite),
but a thick coat of wet paint before assembly will also do.
of three groves with a saw cutter for the horn cheeks of the
trailing axle. A small piece of scrap metal was used to make a fixture for
holding the cheeks (brass angle) in the correct position during cutting the
slots. In these slots some small webs were inserted and soldered. Only two
small tool clamps were used to actually hold them down during the milling
process. The large saw cutter was used at a slow speed.
trailing frame of the little 0-4-2 engine. The horn cheeks
and axle boxes were built up from brass. Aluminium-bronze bearing bushes are
glued in to the axle boxes. I still have to solve the problem how to make
the working leaf springs. The two small boxes on the rear are battery boxes,
which were used (on the prototype) to power the ATC (=Automatic Train
block for making the smokebox saddle. It takes up some time,
but it's nice to watch the shaping machine at work and it is of course
capable of taking large cuts at a time. Usually I use some suitable scrap
metal for making these parts.
the smokebox saddle on the milling machine. It was first
shaped from solid (again avoiding the casting, due to the high price of
importing). The radius (for taking up the drum type smokebox) was also first
roughly shaped in form, before turning to the boring head. This saves a lot
of time, because the boring head can’t take large cuts.
crank axle on the wheels, set at 90 degree angle. For this
procedure I used ACAD to calculate the height of two pillars, which in their
turn make sure that the crank pins are set at 90 degrees and (more
important) that both wheel sets are exactly the same. It worked out
perfectly, with no adjustments needed on the coupling rods. The set-up for
glueing is made on a machine table (an old spare from a shaping machine),
which ensures that the wheels (of which the flanges fall partly in the
T-slot of the table) are in line and don't roll away during the setting of
the glue (Araldite).
chimney on the smokebox, using a large bolt to press (and
hold) it down on the smokebox. It was turned from solid steel. The bottom
flange of the chimney was turned very thin (approx. 1 mm) and was ‘squeezed’
on the smokebox until most of the circumference was in contact with the
smokebox drum. The bolt hold it in place, when I was beating down the last
part of the flange with the aid of a steel hammer and a brass rod (about 1"
in diameter). No heating up was required.
block under construction, made from solid bronze bar. Due to
high price of the cylinder set, I decided to use bronze bar instead. (At the
beginning I even considered free cutting chrome steel, which I had, but by
e-mail correspondence I got convinced not to use this). Most of the work was
done by the shaping machine, which is able to get a smooth surface (especially
for the port face). The bore (30 mm) was made on the lathe in a 4-jaw chuck.
I am thinking of using O-rings for the piston rings.
on the former
during the beating process. Two steel former plates are used to hold the
plate in place in the vice, during the beating (done with a Nylon hammer).
The former plates are made of 10 mm thick steel. The copper plates are 3 mm
thick. I understand that for 5" gauge it will be a small boiler with an even
smaller firebox. The flanges were made to length, after they were formed. In
this case the blanks can be roughly cut to shape, when starting with
fabrication of the plates.
in a temporary fire hearth for annealing. Heating up was done
by a large Sievert propane torch. The annealing was repeated three to four
times, to get the final shape. The annealing itself is nothing more than
heating up to bright red and let it cool down again. This softens the copper,
so it won’t ‘crack’ during the forming process. The fire hearth itself is
not much more than a couple of firebricks temporarily placed together.
plate after forming from 3 mm thick copper plate. The ring
for taking up the boiler barrel was formed first in a steel ring. A disk on
the former plate (with an outside dimension, the same as the inside diameter
of the ring in the copper plate) held the throat plate in position during
the beating of the outer flange. With this method everything will be nicely
lined up during assembly and the connection between boiler barrel and throat
plate will be strong.
loco as it was at our
'open day' at Breda in June 1997 (the Netherlands), with an GWR 45xx class
Firefly. You'll see there is still a lot of work before she will go.
the loco frame at our annual steam meeting June 1997 in
Breda. Driving my 3 1/2" 'Mona' took up a great deal of the day. But there
was still time to take this photo. Our Steam Society 'Stoomgroep Zuid' has a
club track in Breda, next to some sport fields. It's an all steel (noisy,
but charming) elevated 5"/3.5" track, with a turntable and steaming bays.
Although it is a good track (266 metres long, kidney shaped, almost level)
and open all year, it is alas not much used by members of our society.
look of the locomotive at a show in
Turnhout (Belgium). Here they have a
large 5" and 7 ¼" gauge ground level track trough a large part of a park.
locomotive as it was November 1997.
The frame is on its wheels (not yet sprung) and the brake gear is partly
completed. This took up much time, because the ordered brake hanger castings
weren't very good. I tried to make them look better (rough casting, out of
line and too large) but this wasn't satisfactory. So I've made new ones,
building them up from steel plate and some bushes. The cylinders are already
fixed between the frames. Due to building a home extension, there wasn't
much time for model engineering in 1997.
There are two ways of doing things:
The wrong way or the Great Western Way
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