We wish all friends and fellow 16mm enthusiasts a happy and
prosperous new year! May our wishes come true and may our worst fears not be
realised. It is also healthy to recall that sometimes it’s better to face the
fear in order to realise our dreams.
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| 16mm Wrightscale Wrens |
We are pleased to say that the latest batch of Wrens is
making progress. They are beginning to look like locomotives. Better still they
have reached the steam test stage, that is, they have nearly become proper
locomotives.
A number of stages mark this journey.
The first one of course is thinking. Well was it said
‘measure a thousand times, cut once!’ NOTED The Wren was built to Imperial
standards so metric equivalents are only approximate.
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| Kerr Stuart Wren nameplate Photo copyrioght MD Wright |
The prototype Kerr Stuart Wren - with a wheelbase of a mere
3’ (90cm) designed to run on 2’(60cm) - was very small. This was intentional.
Competitors abroad, especially Decauville, Jung and Henschel, were world
leaders in compact locomotives and the British couldn’t afford to miss out. In
1905, Kerr, Stuart started to adapt an existing design, the 0-4-0 Buya Class to
produce a locomotive to run on 2’ gauge. The early Wrens were built with
low-slung boilers and cylinders. They had Stephenson’s reversing links. The
wheels were one-piece with a group of four holes. This was a problem. Because
of its dainty weight – 3 ton 7 cwt (just above 3 metric tons) - the locomotive
tended to ‘sit’ on its back wheels when starting off with a heavy train. This
led to uneven wear. Soon, the wheels had steel tyres fitted, making them
slightly easier to re-machine.
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| This 16mm Wrightscale Wren is a model based on the new type built after 1915 |
In 1915, the ‘new-type’ Wren was introduced. It benefited,
dare we say, from improvements inspired by Continental practice. The boiler
barrel was lifted 7 ½ “ (19cm). This made it a little less vulnerable to debris
on the track, but also made for a more robust frame. The cylinders were
inclined, again, allowing greater clearance between them and the track. Proper
cylinder drain-cocks were possible. Previously they drained through the front
covers, an arrangement which encouraged a cloud of steam around the front and
corrosion.
In all, 58 of the old-type were built and 104 of the
new-type before Kerr, Stuart closed. Prototype size Wrens are still being
produced thanks to the engineers at Statfold Barn – but that is a story in
itself! In spite of improvements, the old-type continued to be requested.
Perhaps some proprietors had no truck with nasty foreign innovations.
We chose to model the new-type for various reasons. One is
the light and airy look. Another is that there are more surviving new-types,
therefore they are better known. They would therefore be more popular with you,
our market, and there is more information around. The last is personal. We fell
in love with ‘Pixie’ at Leighton Buzzard on a family expedition back in 1980.
The Wren’s history and our choices inform everything about the model.
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| Part-built 16mm Wren locomotives in the workshop, January 2019 |
The frames for each locomotive are the first part. This
includes fitting the axles and the wheels without which there will be no
movement. As becomes a new-type model, the frames are relatively tall. They
also have a prototypical (sort of!) strengthening web. We know that the
completed model will be treated with respect, but accidents do happen, on 16mm
lines as well as 2’ gauge!
Here has to follow a slight disclaimer. The frames and
strengthening web vary slightly from the prototype – not being completely
faithful 1:19 scale models. In scaling down, some liberties have to be taken.
The overall dimensions, if scaled up, would be too robust. Look at it this way.
A healthy, functioning baby is not a scaled-down version of a healthy,
functioning adult. In the same way, producing a live-steam 16mm scale
locomotive requires some trade-offs.
Next come the cylinders, a surprisingly ticklish job as this
stage includes fitting the connecting rods. Next, the valve chests and pistons
are fitted. This is science and art combined. Each piston has to ‘feel’ loose
in the bore but, of course, not too loose. As mentioned above, for the best
reasons, the prototype cylinders are inclined, which adds to the joy of
building!
Next is making up the valve-chests and steam Tee then the
fitting of each connecting rod. It is vital to get it right. The valve gear can
now go together. At this point, the Hackworth link must be fitted. As we saw
before, this small alteration made a big difference to the Wren. The reversing
shaft was moved to a place above the driving wheels, a reason why the
locomotive has its airy appearance.
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| Batch of 16mm Wrightscale Wrens in the workshop January 2019 |
Fitting the link requires work with a file. ‘Square up and
bevel gently’ is the advice – the artist’s hand is needed here. The valve-gear
assembly must move freely but with very little shake. Only then can the
valve-rod be fitted. A little art is needed here to avoid the opposing evils of
sloppiness and binding.
Now the valve events can be set. Oddly enough, there is
something of the skill of riding bike here. While one side rests, the other
comes into play. There should be two points in the complete cycle where the
ports on both side are open equally. Here, the analogy with a bike breaks down.
A locomotive can operate in reverse; a bike doesn’t. The valve ports must have
their equal points both when going forward and in reverse. Actually, as with the
prototype, you do want the best running forwards. You may achieve this by
beginner’s luck, or by careful adjustment.
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| Wrightscale16mm Wren in green livery |
So far, the locomotive has been put in reverse by holding it
up-side-down and reversing the motion. This is not, to put it mildly, prototypical.
Now the reversing lever can be fitted, then the saddle of the boiler. Once the
boiler is fitted, the locomotive begins to look recognisable. Better still, the
locomotive is on the road towards its first steam test. Stand by for further announcements!
