Newsletter - National Field Archery Society

8
The Birth of the Compound Bow
IT’S hard to imagine any other single invention that has
so impacted any sport like the compound bow has influenced
archery.
But Holless Wilbur Allen’s new bow design did just
that, it revolutionised archery. But the invention didn’t
come easily.
Holless, a mild mannered Missourian, was frustrated,
like many archers, with the low speed of his arrows. He
set about trying to increase arrow speed by designing
and building different types bows and testing his ideas.
First he built a recurve bow, laminated with fiberglass
rovings which he bonded to the limb core with epoxy. No
luck. He then tried fabricating a long handled bow with
very short, extremely recurved limbs to increase arrow
speed. Again, with no success. He finally tried shooting a
short, lightweight arrow down a track attached to his
bow. He had some increase in speed but poor penetration.
This testing broke his bow, too! But nothing gave
him the speed he was looking for.
Wilbur Allen was a tinkerer, and his innovative spirit
drove him to while away many hours contemplating a
better way of building a bow that would shoot arrows
faster.
It really comes as no surprise that lightning would
strike one evening in 1966. The eureka moment came
about while Wilbur was studying his drawings of a pulley
bow, designed after reading up on kinetic energy in a
physics book borrowed from a neighbour.
“What if,” he thought, “I positioned the pulley’s pivot
hole off-centre?” That was it! Within two days, Wilbur
Allen had built and tested his compound bow. It was
crude, even by Allen’s standards – the eccentrics were
of wood, the handle of pine boards, limb cores of oak
flooring, and welded T-bolts held it together with the
help of Elmer’s Glue and epoxy-impregnated fibreglass
threads. But, it worked!
Allen achieved significant increase in arrow speed over
a recurve bow of equal draw weight, relaxation of draw
weight at full draw of 15%, and a bow that would shoot
lighter arrows than the equivalent recurve. His compound
produced impressive performance.
Allen filed for a patent on his new bow on 23rd June,
1966. It was granted in 1969. By 1977, there were 100
different models of compound bows available, only 50
recurves. After only eight years in production, two
thirds of the bows on the market were compound bows.
As Holless experimented with different ways of using
the pulleys, he discovered that by using one with an offset
axle (eccentrics), he created one of the biggest
advantages of compound bows - the let-off. When coupled
with a cam shape instead of a round pulley, the
draw length, weight and force curve could be changed
and improved.
by Derek Scaysbrook
After several years of trying, Allen couldn’t find anyone
to manufacture his new invention, the compound bow, so
Allen began making his own bows, sure in the knowledge
that they would catch on.
However, when he was making his own compound bows
he realized that he had a error in the design, as he kept
on stripping the fletching off his arrows. The crossing
cables in the centre of the bow were interfering with
the arrow's flight. By 1967 Allen had figured out that
he needed to add an extra set of ‘idle’ wheels that were
mounted at the centre of each limb. These idle wheels
were set at 90 degree angles to the limb-tip, and this
allowed the cables to now cross to one side of the centre
line so that they no longer interfered with the
arrows' flight path. With more research, Allen added
riser-mounted adjusters so that the archer could use
different cable lengths to attain different weights.
These adjusters were gear-driven and acted very much
like the machine heads for tuning a guitar.
Holless Wilbur Allen had laboriously contrived a rather
complicated device that performed a relatively simple
task – to shoot an arrow faster.
Derek Scaysbrook