Building the 'Mad Mallet' 'River
Mallet 'River Avon'
click on image to enlarge
click on image to enlarge
The 'Mad Mallet' began as a joke on the
Lynton and Barnstaple forum about articulated locomotives that could
been built. I was stuck with my work and had a spare hour to get bored
and watch telly, so I drew an L&B Mallet on my laptop with the company
of Judge Judy. Rather embarrassingly, I fell in love with the design.
line drawing of 'River Avon' and 'River Brue' - click on image to enlarge
I have always rather liked Mallets. As a
kid I had the privilege of seeing Challengers blast through the Rockies.
You never forget a thing like that! Garratts might be a better design
but I have never warmed to seeing locomotives with two backsides.
The Mallet has its origins in France. The design minimised the number
of flexible high pressure steam pipes and limited their movement by
having the rear power bogie fixed to the boiler so only a small
flexibility was needed. The design really favoured the use of
compounding. The system reused the low pressure steam to operate a
secondary drive using much larger cylinders. By the time this engine was
built (1920s) greater efficiency would have been extracted by the use of
Mallet locomotives were used with success
on a number of European lines, mostly narrow gauge, but really came into
their own in the USA. Here they were a huge success as they permitted
the Americans to have the biggest in the world without needing any
imagination of their own!
The heavily graded line of the L&B required
double heading if any sizable trains were mustered: an expensive
business. Had traffic been greater, it would have been quite possible
that Eastleigh would have contemplated building more powerful traction
units that still had to operate within the loading gauge and go round
the numerous tight curves.
The L&B benefited from the development
experience of Welsh narrow gauge railways. The one mistake made was the
relative lightness of the track. The only way to get more power would
have been to have more wheels. The Mallet could have been considered.
This is not a complete step to step
instruction sheet, but hopefully a guide as what you can do with etched
kit bashing, in this case a Backwoods Miniatures Manning Wardle was attached to two ROCO outside frame chassis. 'Avon' is
freelance. Its looks ring my bell but not necessarily those of others.
Hopefully, though, it does give a stimulus to others to 'have a go'.
Anyway, if you mess up the Backwoods chassis (like I had), this is a
possible use for the remaining body!
Sadly, the Roco chassis gear mechanism
turned out to be 'not fit for purpose' and after a few hours of
excellent running began to develop gyrations every bit as good as binge
drinkers falling out of a pub! I had intended to rebuild this locomotive
with the new N Drive outside frame six coupled chassis. I have seen the
prototype and in my view it is an excellent basis to start with. Sadly,
some production delays have arisen and the rebuild will use two Bachman/Grafar
08 class diesel no 371-015 incorporating the cylinders and valve gear from the
scrapped Roco chassis.
I do not have specialist equipment and this
locomotive is made using the most basic of tools. Most were bought from
25 watt soldering iron with 2mm end.
needle nose pliers
larger needle nose pliers
set of small screw drivers
set of small drills
fine craft saw and modelling knives
small set square
small engineers block
wife's best scissors
Dremel tool with attachments
set of small burrs
Badger air brush
thin multicore solder
plumbers liquid flux
5 minute epoxy
Remove the two cab sides from the fret. The
cab sides of the MWs as delivered are used.
After removing the bunker top, squarely cut
off the rear bunker and solder into position. Cut out two pieces of
brass 10mm X 22mm. Tack solder them accurately together and transfer the
curve of the original bunker to the replacements. Sand the new bunkers
to that profile with a Dremel and separate. The new bunker can been seen
in the photo above, top right. These are then soldered to the rear of
the cab sheets. I solder panels with the work lined up against a steel
rule to ensure straightness.
Now cut the front of the cab down as shown
in the photo above.
Remove the vertical bars from the cab side
windows and file to profile and solder to the cab sides. Solder in the
bunker doors and the cab side handrails.
Now cut the tank sides, 65mm X 12mm. Solder
these accurately to the cab sides, 2 mm from the bottom.
The bunker back is fabricated from two of
the etches, including the one which has etched lines to make following
the curve easy. The excess is cut off. The cab back has had the lower
section removed to allow for the mechanism. The small return is saved to
The cab front is soldered into place. Great
care is needed to ensure that the whole assembly remains aligned. I
always solder on the spectacle frames is first. I line these up by
pushing a paint brush handle through the hole!
Add the tank tops, 7.5 mm X 52 mm
Solder in the tank bottoms 7.5
mm X 64 mm. and the tank backs 65mm
X 12mm. Then close off the back of the bunker as shown below. Cut excess
off flush once soldered.
Now build up the bunker sides using strip.
Prepare the boiler barrel, solder on the
bands made in thin strip and solder the barrel into place. Solder in the
floor and enlarge the central hole to accommodate the chassis.
Now add the boiler supports, water fillers
and the smokebox, (made from the same material, slit at the bottom and
opened out a little.
9 hours into project
The tank is drilled to take the handrails,
and lamp irons and foot steps are fitted. Cut the cap off the chimney
and reduce height so the complete casting remains in loading gauge and
The MW smokebox is just too small. A plain
disc was made by cutting one out of thin sheet with scissors
(wife's best), drilling the centre, spinning in the Dremel in a mandrel
and sanding until round and the right size. Then a second disc was made,
a tad smaller than the first , one side covered with solder and sanded
on the Dremel until the right door profile was obtained.
Drill a hole in the smoke box top in the
correct position and glue the chimney into position.
The two steps on the tanks' fronts are
The new door is then epoxied into place.
The door hinge and straps are made from thin strip and wire, soldered up
and glued on.
The rear coal bunker retaining rail ,
whistle, safety valves and interior cab details are then fitted . The
roof is then soldered on having been trimmed to size and the roof vents
soldered in. The sanding pipes are then soldered into position. The
'Russell' sandpots will be mounted on top. Also fitted is the plumbing
for the steam draincocks. The front bogie support footplate has been
added. The thin wire rubbing strip has been soldered underneath in an
arc the radius of the front chassis pivot.
click on image to enlarge
17 hours into project
click on image to enlarge
The front pilot is built from spare bits of
Backwoods cabs (with an etched fold line) and awaits the cowcatcher. The
pilot will be attached to the front chassis.
Piping strips are added, using very
thin brass strip. The 'Russell' dome is not attached until after
supporting brackets soldered onto
finished bar one sandbox - click on
image to enlarge
I hate white metal vacuum
connectors. This is particularly the case with MW locomotives which have
these items unsupported on the front buffer beam. I always make these in
brass wire and wrap 3 amp fuse wire. Flanges and connectors can also be
modelled by wrapping a ring of fuse wire at the location of the flange
and touching with solder.
When soldering a small bit onto a larger
bit, tin both surfaces. Sand the surface of the larger bit smooth, add
flux, place on the small bit and heat with clean iron (wipe off solder
with cloth) until you see the solder fuse.
If you get solder where it should not be,
(and you will), it will sand off with the sander attachment of the
Dremel or using a burr, you can use 150 grade freecut sandpaper, and for
small spaces use a modified craft blade, break off end and use as a
First things first. True
Mallets are compound locomotives, so the front cylinder shape has to be
modified. From the Backwoods fret, select another rear bunker which has bending
lines and cut two rectangles to the correct size and bend them to obtain the
Sand or file off all the
details of the cylinder ends of the front chassis.
the retrofit of two new
Grafar 08 chassis
The Grafar chassis is easy to dismantle and
the first was cut back and the high pressure cylinders fitted with epoxy. Great
care is needed to position the cylinders to ensure that the correct movement of
the valve gear is possible. They have to be as close to the front crank as
possible. The rear coupling rod pin was removed and the hole opened out
slightly on the crank to accommodate a brass wire pin. The chassis is well made
and the drive is on the centre wheel. This does mean that additional strain is
taken on the rear axle with the valve gear.
The Roco valve gear easily grafted onto the
chassis and seems to run very smoothly.
I have experienced several loose wheels. This
is what I suggest:
On initial stripdown, degrease axles and wheels and run into the wheel
boss, a small quantity of Locktight 603 and leave overnight. This should
prevent these stupidities.
Several phosphor bronze are often on in contact with the wheels....check
Positioning of the Roco cylinders. Remove
motor. Use 5 minute epoxy to attach and have the return crank already
fitted into the rear crank. There is then a short window of opportunity to
ensure that there is free movement of the gear.
Once the cylinders are fastened, push the chassis along to check for any
binding between the coupling rod and the slide bar support bracket. Only
then replace the motor but glue this in position as well, as the extra
weight of the valve gear can cause the motor to 'jump' and strip the
the new chassis arrangement with lead weighting
the loco after successful trials and ready to
return to service - click on image to enlarge