http://www.getwoodworking.com August 2019 The Woodworker incorporating Good Woodworking 83
projectile towards Sterling Castle, are all
created by CGI (Computer Generated Imagery).
In the Netflix photos you see the replica Edward
I called ‘War Wolf’, built by Fergus and his team.
In the 14th century it was believed to be the
largest trebuchet ever built. CGI is later used
in this example to add the detail of Stirling Castle
in the background (not visible here) as well as
simulating the actual firing by the actor (Stephen
Dillance), who plays Edward I, as he cuts the
securing rope of the firing arm with his sword
to release the burning projectile (photos 7 & 8 ).
Overview of the main components
The chassis (base) is a diamond base comprising
of 300 × 300mm Douglas fir beams that measure
8.8m along each axis around its perimeter, which
are held together with mortise & tenon joinery
(photo 9). The perimeter beams are tenoned
into the lateral spine beam and then pegged. The
spine beam uses 400 × 400mm beams and has
an overall length of 12.6m. This is made of two
pieces, which are scarfed together (photo 10).
On top of the chassis is a ladder frame running
longitudinally. The ladder frame comprises
of two beams (12.45m) running parallel to one
another with intermediate crossbeams, 300 ×
300mm, linking them together (photos 11 & 12 ).
The ladder frame is jointed with through-tenons
and wedged keys, and cogged over the perimeter
beams using simple 38mm lap joints. Attached to
the firing end is a guide chute (photo 13). A guide
chute guides the sling through the frame and
supports the enclosed projectile until acceleration
is sufficient to hold it in the sling. At the same
end a trigger arm is to be found (photo 14). This
is primarily a small A-frame on which the firing
arm bears when the trebuchet is tensioned and
ready to fire. A shackle and pin holds the firing
arm down to the A-frame and when released,
the trebuchet fires (photo 15). The ladder frame’s
main function is to support two A-frames, which
are the primary vertical structure of the trebuchet.
These are mortise & tenoned into the frame
ladder at the bottom and wedged and keyed to
the cross member towards the truncated top
(photos 16 & 17 ). A central vertical inner axle post
for the treadmill is mortised & tenoned into the
cross-beam of the A-frame and frame ladder.
There are further axle posts on the outer sides
of the treadmill, and these have a wheel height
of 4.5m (photo 18). By comparison to other
primary components, they are much smaller
in section, typically speaking from about 35-
200mm. Fergus explains how the A-frame,
in turn, provides the support for the axles and
treadmills (photo 19). As the film employed CGI,
there wasn’t any necessity for the treadmills14 Trigger arm
20 Axle block in construction17 Wedged and keyed A-frame19 The treadmills rotate on axles either side
of the truncated A-frames. Note the axle block16 A-Frame wedged and keyed with traditional
joinery18 The treadmills have a height of 4.5m
15 The trigger arm is very visible on the Warwick
Castle trebuchetto turn. Nevertheless, the team made it so
they could. The treadmills rotate on axles either
side of the truncated A-frames and are held in
place by an outer and inner axle post and axle
blocks (photo 20). The outer axle posts also
have supporting diagonal struts to give cross
rigidity to the structure (photo 21).Prior testing
Before any work was undertaken on the
trebuchet, a working scale model was built
by two of Carpenter Oak’s travelling French
carpenters from the Compagnon du Devoir (see
foot note). These trainee carpenters made a 1:5
scale prototype of the trebuchet, complete with a
finely-tuned counterweight, which when tested,
was capable of firing a projectile 45m (photo 22).
“As a result of building a fully working replica
model 1:5 scale, we were confident,” Fergus tells