Gentlemen & Ladies,
>
I have a question and proposal for discussion. We manufacture fencing
rapier blades for the re-enactor, Renaissance fair,
SCA community. Recently we began manufacturing side sword blades for cut
and thrust fencing and have run into a problem.
>
We previously made blades for parry and thrust fencers and had little
difficulty meeting our customer's requirements. Customers could specify
blade length, stiffness, weight, and balance point and we could pretty much
supply what they wanted. With parry and thrust fencing much of the energy
in a parry or thrust is tied up in the fencer's body and so the speed of an
attack or defence depends as much on how fast the fencer's body can move as
on the motion of the weapon.
>
With the new cut and thrust fencing though the weapon is actually rotating
around the axis of the fencer's wrist. The rate at which an attack or
defence takes place therefore depends partly on the moment of inertia of
the blade. Two blades can have the same mass and the same balance point
but very different moments of inertia. For instance a falchion and a long
rapier blade can have the same mass and the same balance point as measured
from the shoulder of the tang and yet the rapier will have a higher moment
of inertia due to its greater length. It will therefore be slower to
accelerate given the same amount of torque applied by the wielder.
>
What we would like to find is a simple way of comparing two side sword
blades in terms of wieldability. In other words we could tell a customer
that a 36 inch blade he is using has a wieldability of 457 while our 40
inch blade has a wieldability of 503, and another maker's blade 514. In
this way a customer could interpolate and better decide whether or not he'd
be willing to go with a less wieldable blade in order to gain 4 inches of
length. The problem though is that moment of inertia is extremely
difficult to calculate since it involved summing cross sections over the
entire length of the blade. I have therefore been experimenting with
simple products of a blades mass, length, and balance point which are all
easily measured.
>
The best numbers I have come up with for comparison thus far is a simple
product of Mass times Length times Balance point as measured from the
shoulder of the tang. For instance in MKS units a 0.5kg by 0.914m blade
with a balance point 0.241m from the shoulder gives a wieldability of 0.5kg
x 0.91m x 0.241m = 0.110 kilograms meters squared. The lower the result,
the more easy a blade is to swing. Of course this product can't be used in
a formula with newtons of force giving acceleration in meters or radians
per second as the result, but it does give a fencer an idea of how this
blade will behave when compared to another of known mass, length, and balance.
>
Are there any other ideas in this regard? Does anyone have another simple
method of comparing blades?
>
Jim Koch, Alchem Inc.



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The CFML is sponsored in part by Purpleheart Armoury, now carrying rapier blunts and leather gorgets. http://www.woodenswords.com
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