Reminiscing The Compound Bow, Part 2



Bowhunting.net

Bob Ragsdale

Reminiscing The Compound Bow, Part 2

By Bob Ragsdale

Aug 21, 2007 – 11:12:18 AM

 

MORE ON GALVANIZED STEEL CABLES

Understand that this was only ?phase-one? of what was to be dozens of
phases over the following years to resolve all of stresses and cracks
and breakage to end up where we are now. Every one of the early
manufacturers had to find solutions by trial and error and address
every situation as it developed.

Figure 2. Even as crude as they were we were all amazed at how quiet the rod limb models were. This is a later model made with stock that was made with a flat area on both sides of the rod but still sanded down for different weight ranges. As a dealer I think I paid around $78 for these models. There was another model with forked, flat, laminated limbs.

There was limb breakage, handle riser
breakage, cable problems, string problems and the accessory market
REALLY took a hit. Sight mount screws had to be enlarged from #8 to #10
to stay tight, and essentially every bolt-on accessory was in dire
straights because the recurve stuff would crack and break after so many
shots. If you have ever seen the slow motion videos and watched the
arrowrests, sights and limbs and handles vibrate you have seen what
caused all the stress. For years it seemed to me that you couldn?t go
to an indoor shoot where you didn?t hear at least one scope hit the
floor after its small 3/16ths inch shaft broke from the vibrations.

I remember way back when Olympus Archery in Houston was struggling with
their laminated limbs that were delaminating and they finally decided
they were squeezing all the glue out when they clamped them to dry so
they added tiny grains of sand or glass to hold them slightly apart,
and it worked.

   

For years the steel cables were not even plastic coated. Even years
later after they were vinyl coated everyone was so paranoid about
cables that essentially ?everyone? would replace their cables before
the start of every hunting or tournament season. There was a lot of
money to be made replacing cables back then.

   

The fact that the modern high-tech string materials ended up being so
much stronger the steel cables are only used as ?buss-cable? on a few
models. The ?buss cables? are the 2 matched shorter ones on 2 wheel
models or the one short one on ?one-cam? models that have the easiest
job in town. The buss cables do no more than hold the 2 limb tips
together while at full draw. That is, if they don?t break during the
draw it never gets any worse, because you can?t rip something in half
by suddenly changing it from ?heavily loaded-to-loose.?

   

For many years every bow on the market sported 1/16th inch diameter 7×7
galvanized steel cabling and some still do today. Back then, breakage
in that portion of the cable used as the longer buss cable section was
essentially unheard of, it was the short ?pigtail? portion on the other
side of the eccentric that connected to the Dacron bowstring that had
the hard duty. You guessed it, the reason the cables broke in that area
was because on the shot it suddenly changed from ?loose-to-tight? and
that heavy stress could take its toll anytime the metal fatigue from
the continual wrapping up around the eccentric became excessive.

   

In one of my projects I needed to reduce the fatigue administered to a
cable and during my research I discovered a same diameter galvanized
cable virtually as strong but MUCH more flexible. The 7×7 mentioned
above reflects that the cable is made up of 7 bundles of 7 strands
each. The cable that was 7 x 14 was 7 bundles of 14 much smaller
strands. Wrapping a 7×7 to where it felt tight was about twice as large
as where the 7×14 would begin to stress. The 7×14 solved that breakage
situation and for years after that I used only 7×14 cables on all of my
families personal bows as extra insurance. Strangely enough, to this
day I still shoot my indoor events with my all-time favorite SMOOTH
feeling round wheel, laminated wooden limb bow with 7×14 cables, which
have not been replaced since 1986 when I built it. That?s 21 years you
know.


BOWSTRINGS

Those cable ?pigtail? extensions coming out of each eccentric to which
we attached the short 32 to 43 inch bowstrings was the weak link. It
really became problematic when we found that changing from Dacron to
the earliest modern material (Fastflight) would increase arrow speed by
3 to 15 fps depending on the peak weight. That extra ?free? velocity
was great, until you made the mistake of shooting after forgetting to
load and arrow or shooting an arrow with a cracked nock to essentially
dry-fire the bow.

With a modern bowstring material attached to a steel cable pigtail you
only get one mistake and it?s over. Where the Dacron would stretch out
and absorb the stress as the bowstring tightened, the modern string
material doesn?t give any at all and since it is several times stronger
than the steel cable, BOTH cables will rip in two at the stress point
where it is exiting the eccentric cable groove. The zinc string
attachments fitting would only rip off instead when it happened to be a
weaken fitting from a bad casting.

That ?free? extra velocity is due to the fact that Dacron bowstrings
actually ?waste? a significant amount of the stored energy during the
shot. Once you realize that there is more weight on the bowstring when
it is setting at rest than when it is at FULL DRAW you can understand
what is happening. To prove the point, at full draw you?ll find you can
wrap the bowstring around your 3 fingers but you can?t even come close
while it is still at rest. The situation is that Dacron stretches.
Stretch means ?becomes longer under load, but retracts back shorter
when the load is removed.?

For more proof, the next time you are around a bow with a short Dacron
bowstring measure it while at rest and then measure it while at full
draw and you?ll find it about an inch SHORTER while at full draw
because the load is so drastically reduced. These days the wrong term
is commonly used when fiber strings or cables settle and have become a
bit longer. Since it will never contract back shorter to its original
length, it has actually EXTRUDED, or CREEPED, to a longer length,
proving that it did NOT stretch.

   

Again, when you draw a bow equipped with a Dacron string you stretch
the string out longer and longer as the weight increases, but as it
breaks over and the weight reduces, the bowstring instantly gets
shorter and shorter which means that the bow has to waste some of its
stored energy to stretch it out again during the shot while the arrow
is still on the string. A rule of thumb I?ve used all these years since
the fantastic high performance bowstring materials became available, is
a gain of about 3 fps on very light target bows but with no more than
about 15 fps gained on heavier bows.


LIMB EVOLUTION

In the earliest days of compound bows public demand was for laminated
wooden limbs. At that time, everyone felt that if they weren?t
laminated wooden limbs they were dime-store-junk like the toy bows we
started our kids out on. It actually took years of slow education to
convince the multitudes that ?glass? limbs were the only way to fly.

When I was involved in the project of getting our first molded glass
limbs into production it didn?t take long to make a believer out of me.
I?ll say the odds are that every bow now on the market with molded
composite-fiberglass limbs (molded so that every fiber strand runs
completely from one end to the other uncut) will still be functioning
fine when your grandkids start shooting your same bow. I often tell of
the early tests where I measured the spine reading of each limb and
then built bows and recorded the peak weight and left them for weeks
jammed at full draw on the factory hot black roof in Arizona and found
they still had the same peak weight and limb deflection figures. Plus
always receiving questions about what happens to the limbs in hot and
cold weather I also found no weight or velocity changes after putting
them in a freezer or a hot truck cab. My point being that in extreme
weather all the other things we can do that cause us to miss are still
in effect, so there is no need to inject a new excuse of extreme lousy
weather.

As you can see, the original Allen limb weight bolts were fashioned
with the recurve bow philosophy in mind. They had a T handle welded on
the bolt head so the weight could easily be removed EVERY night. We all
looked and felt stupid standing there counting out the 8 or 10 turns
out and then back on the next morning, hopefully back to exactly where
it was before. In my circle of friends at least that silly drill lasted
only a few weeks before we said ?to heck with that nonsense.? None of
us realized at that time that it was actually the reason we had so much
trouble keeping our sight settings accurate, we had no idea that moving
either limb bolt any at all from where the settings were made would
move our nocking point up or down and move us off our sight scale.

   

A section of stock fiberglass round rod sanded down flat on one side to
weaken them to the stiffness needed was simply glued into a block of
wood on one end with an aluminum plate folded over the other to hold
the eccentric. We often used knives and files and sandpaper to fix
splinters and glass strand ends in gouge damage and then just kept on
using it without a problem. Hey, a pound is a pound wherever it comes
from.

***image3***

(caption 2)

Figure 2. Even as crude as they were we were all amazed at how quiet
the rod limb models were. This is a later model made with stock that
was made with a flat area on both sides of the rod but still sanded
down for different weight ranges. As a dealer I think I paid around $78
for these models. There was another model with forked, flat, laminated
limbs.  

  
MORE FUNCTIONING

The only, real, official velocity rating system is the AMO test. Using
only the 30inch draw, 60pound version of each model, a 540 grain arrow
was clocked at one yard out. It was great in the sense that you could
just figure that no matter what peak weight or draw length you were
buying your draw length would be proportionally slower or faster than
the difference in the 2 models you were comparing. Rule of thumb was
that for every inch different in draw if you used the same 540 grain
arrow it would be 5 fps less and for every inch shorter and 5 fps
faster for each inch longer, so you could compare models in that manner
if you were not a 30 inch draw yourself. All of these early models were
rated from about 190 to 200 fps back then, but no one ever asked, or
cared.

THE RACE IS ON

The ?tweaking? begins. The first mechanical advantage added was to
?ruin? the hard working, smooth drawing round eccentric and then
calling it a ?cam,? which all eccentrics actually are. This increased
the ratings to about 209. Then, the brace height was lowered an inch or
so which added another inch of power stroke and raised the rating to
about 214. Then when Dacron strings were replaced with a modern high
tech no-stretch material about another 15 fps was gained under the same
AMO test which pushed the speed up to about 229 fps where we remained
at a stalemate for some time.

   

Making the ?cams? even harder to draw and lowering the brace height as
low as the traffic will bear has pushed them up to very near 250 fps.
With the speed craze epidemic created by the 3D target crowd, creative
marketing took over and introduced an unofficial rating system that
virtually no customer understands that makes these very same models AMO
rated from about 235 to 245 look much more impressive by using figures
slightly over 300 fps. A very few catalogs do actually list both
figures for their models.

You can see there is no magic, it is all hype and maneuvering. The
capability of every model is simply a matter of how many of the very,
very, few tangible mechanical advantages you allow it to contain.
Essentially, for years now the only game left in town to increase the
velocity rating is to muddy the water with specs and to further ruin
the efficiency of the wonderfully smooth ROUND eccentric to make the
archer draw and feel more weight during the draw. That ?free? extra
velocity doesn?t come easy, NOTHING is free. 

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