Ancient Siege Engines
In the catapult I am describing, the dimensions of each winch are :
Large Wheel. - 14 in. diameter across its top surface.
Its bore (i.e. the aperture for the skein of cord), 8 in. diameter.
Total length of the wheel, 8 in.
Length of its flange that fits through the iron plate, 3 in.
Thickness of the flange, 3/4 in.
Pinion Wheel. - 6 in. diameter. Its length, 4 in.
The projecting ends of the spindles of the pinion wheels are each 2
in. square and 5 in. long. On these ends heavy spanners are fitted for
twisting up the skein of cord. See Frontispiece.
The cross-bars fixed across the apertures of the large wheels, and over
which the ends of the skein of cord pass, are each 10 in. in length, 4
in. deep and 1 1/4 in. wide across their tops.
They decrease to 1 in. in width at their lower edges and are, therefore,
slightly sloped at their sides, as shown in IV, fig. 197, page 286. These
cross-bars fit like wedges, into the slots cut to receive them inside the
large wheels of the winches, fig. 197. They are rounded on their exposed
edges so as not to fray the cord they hold and, of course, they equally
divide the apertures of the wheels.
Though this was the method of fixing the cross-bars adopted by the ancients,
I have had my winches cast with their cross-bars solid with their wheels
and not as separate pieces.
The wrought-iron plates through which the flanges of the large wheels
of the winches pass and on which the projecting rims of these wheels revolve,
are each 1 in. thick. These plates are bolted to the sides of the catapult,
fig. 202, page 298.
The round shanks of the spindles of the pinion wheels (secured at their
ends by washers and nuts), also pass through these plates as well as through
the sides of the framework of the catapult, II, fig. 197.
An almost inconceivable strain can be applied to the skein of cord by
four or five men turning the winches of the catapult, a strain so immense
that no arm of serviceable dimensions could be made to withstand the force
that would have to be applied to wind it down.
Some medieval writers describe the devices formerly employed for reducing
the friction created between the rims of the large wheels of the winches
and the iron plates on which they revolve.
In the catapults I have made, I have not however found anything of the
kind - such as ball bearings - necessary, other than plenty of grease inserted
between frictional surfaces. |