Exploding Bow Limbs



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Bear Archery

Exploding Bow Limbs

By Wade Nolan – Bowhunting Biologist

Dec 20, 2008 – 7:08:13 AM

 

If you have been shooting a bow for a while you have heard stories of compound limbs exploding, shattering or splitting. I was at the IBO World last summer and I wasn’t there ten minutes when a friend told me about his top “thin” limb failing. Some bow companies have had entire models recalled because of exploding limbs.  This problem is not relegated to a single bow company because nearly all bow limbs are made by two manufacturers. They use the same old technology that has been in use for a decade. The philosophy is flawed. Do it like you have always done it, and you know the rest…

Here is the crux of the flaw. Fiberglass is made up of a collection of linear glass fibers held together by a filler or chemically activated resin. The pieces are laid up in a rectangular plate form and then cured and sawed into the shape or size stipulated by a manufacturer. Bow manufacturers then try to match them by weight and width. The fact that they were cut into the shapes stipulated by the bow company means that if the limbs utilize a flared design or an engineered shaped width, the billet of fiberglass must be sanded or shaved.

This cutting across the bed of fibers  weaken  the limb. It works the same way when building a Self-Bow. If you cut through a ring of new wood and into another layer the bow will fail when drawn. The integrity of the power of the wood was violated and it will delaminate.

This hobbles bow engineers because shaping the limb means weakening it.  If designers  leave out the engineering, then you have a limb that is operating at the lowest common denominator of performance. It is a real dilemma for bow manufacturers  because the technology they are relying on is out dated.

Bear Marketing director Ross Rinehart (R) and Bear Engineer Ben Blosser (L) show Wade Nolan the new Flare Quad Limbs on the Truth 2.

It is difficult to do a CAD supported Finite Element Analysis  on a billet of sawed inconsistent fiberglass. These poor companies are stuck with a percentage of limbs that will eventually explode or splinter. By now you are wondering if there is a solution to this common problem. There is an answer and it was developed years ago by a pioneer bow company who once operated out of Michigan. That company is now located in Gainesville Florida.

We know it as Bear Archery Fred Bear was one of the first to use fiberglass in recurve limb design. An interesting story is told of a failure he had with his first batch of new fiberglass reinforced bows. Fred had a choice to make and he choose to borrow enough money to replace all of the flawed bows he had made and sold. This showed his customers that he had integrity and helped insure a loyal clientele. The limbs that are made every day at the Gainesville plant are still full of that integrity.

Massimillo of Bear Archery examines the Flare Quad Limbs before they are dipped and installed on the new line of Bear Bows.

The solution that Bear engineers invented and patented is a  system where the same strand of glass reinforcement  extends all the way through the limb from one end to the other. The Bear engineers were able to design limbs with dynamic flares and power positions that had no cut fibers. As a matter of fact, the Flare Quad Limb Technology that Bear uses allows them to do something that no other bow manufacturer can. They can rely on CAD based Finite Element Analysis to predict performance on an authentic computer model that is based on a uniform and consistent limb structure.

Then the Bear engineers  took it another level and developed Compression Molding Technology. Now heat and pressure  are added to the engineered glass filled resin and the limbs are as similar as identical twins.

This consistency and uniform strength allowed them to go one more step that other bow companies haven’t even considered. My Bear Truth 2 has quad limbs … 4 individual limbs. If you notice, the wheel on the top is drastically different from the Perimeter Weighted Modular Single Cam on the bottom. What makes you think that the dynamics at work on the top limbs are the same as the dynamics on the bottom limb? Correct, they are very different and the stresses and power stroke of each is translated into the arrow launch differently.

These compression molded limbs allow you to see the continuous fiber design that gives the Bear limbs the integrity they are known for.


The patented Compression Molded Technology allows the Bear engineers to design specific limbs for individual performance. Continuous fibers in an engineered platform designed to generate limbs with both individuality and power.

That is why the Bear engineers have designed the top limbs to be engineered as top right and top left … and bottom left and bottom right. Four unique limbs engineered to work in unison to produce a smooth consistent launch every time. The kind of consistency you want when you anchor on a quality buck at 35 yards. A formula that will perform the same every time and never explode. You have never heard of a Bear limb shattering have you. Now you know why!

Footnote: I shoot a Bear Truth 2 and it is the most consistent, forgiving and accurate bow I have ever shot. I have been shooting a bow since 1960 and I have never been more confident than with my BT2.

For more go to: Bear Archery

 

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