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gibson 787
08-12-2010, 02:25 PM
I read this on AT. It comes courtesy of Joe PA. Hope he doesn't mind but I found it very interesting in light of the changes Martin have introduced.


The limb stores energy by having the "belly" side of the limb, the side toward the shooter, compress. The "back" (terms used by traditional self bow makers) of the limb, the side toward the target, stretches. In addition, in "solid" single limbs, you have the fork of the limb which must be reinforced so that it does not split due to imbalances and/or stress to the individual sides of the "Y". A ton of bowmakers have used single glass blanks to make "solid" limbs for a long time, and it worked fine. Now that we are expecting even "slow" bows to shoot over 300 fps IBO, those limbs are getting stressed pretty hard and there can be problems. Also, the parallel limb design causes the bowmakers to shorten the limb a good bit over older, more traditional limbs. The higher prestress to get speed compounds the stress on the limbs. There are different grades of glass from gordon, but I think S glass is the highest grade. The laminated limb, like a Barnsdale, shines in the "solid, short" limb because the laminations can be built so that each layer is suited to its job. A higher carbon layer can be added near the "back" of the limb, because it is good in tension. The six layer limb would have thinner laminations, allowing you to customize the material to the part of the limb that it was put in, but you would have more glue surfaces to hold up. The solid, short, prestressed limb has good resistance to twist or torque, but it has to be very well made to live long, since it bends a lot in a very short part of the limb's length. The Y part of the limb doesn't really bend much, if at all. The laminated limb can be stronger in this type of design. It is limited in strength only in the materials used, and the strength of the laminating process itself. One danger to laminated limbs is the possibility of delaminating in the heat of a trunk or car interior. PSE makes probably the most prestressed limbs on any bow today with the X-force series. They are supposed to be solid glass (I think S-glass, but that is a guess). I have read that PSE limbs could not be made of laminated construction, and survive that prestress and severe bend. One thing here is that they are split or quad limbs. They don't have to have that "dead", reinforced fork area, so nearly the entire limb can flex instead of just a short portion of it. Hoyt's limbs are laminated, split limbs, and they have an excellent rep for durability and performance. They are just not as highly prestressed as the PSE limbs. Hope that helps a little and someone with more technical knowledge will add to it.

Hope you all enjoyed the read.
Dave

Destroyer
08-13-2010, 03:47 AM
Hoyt's limbs are laminated, split limbs, and they have an excellent rep for durability and performance. They are just not as highly prestressed as the PSE limbs.

I think it would be hard to make such curved limbs as PSE laminated, but not impossible. If anyone could its Hoyt. I think that the 'pre-stressed' is just marketing hype. Having the shape they do allows for low brace height, past parallel, nothing more.

I read that the X's limbs are machined, don't know what grade or Gordon glass they are. Would be good if Martin uses Gordon but I'm not holding my breath.

Quads are good. ;)