Gordon vs Bearpaw

[Shredd]

What are your thoughts on Gordons vs Bearpaw Glass??  I know someone did some stiffness tests of the glass on one of the forums??   But did anyone do a performance test on two of the exact same bows using both types of glass??  I am not interested in the clarity of the clear glass just the performance characteristics...

[Flem]

Here is what I know Shredd. It's a post from the past.

"Stic, here is what I have found out about Bow laminates. Gordons is 70% resin, 30% fiber by weight.
Bearpaw is 75% fiber, 25% resin by weight. I have discovered thru experimenting that the compressive strength of the resin adds more draw "weight" than the tensile strength of the fiber does".

I have not used Bearpaw glass, so cannot comment on performance. I have tested homemade glass and Gordons with a tensiometer and can tell you Gordon's has less deflection than my homemade glass, but my glass is heavy on fiber like the Bearpaw.

[monterey]

Everything I have built with bear paw has come in about 8% under expectations.  Not a criticism, just an observation.  I  like bear paw if clear is in the recipe.

[kennym]

Yep, what monte said here, most of my bows are 45-50 and I add 5# to stack to come in...

[Shredd]

Kenny...  Are saying that you add about  .015" to the stack with Bearpaw to make the same weight as Gordons???

[kennym]

Depends on the bow, stack change is different on different bows so I go with a 5 lb heavier than Gordon’s makes .

[Crooked Stic]

My guess is a 45 bow with either glass will need a chrono to see the difference.

[Bow man]

As others have said bows will turn out light with the same stack as Gordons, but it is much clearer.  As far as performance we have seen no difference.

[Stagmitis]

Would be interesting to see the weight aspect between the two

[Flem]

I'm thinking the difference is more significant than just the draw weight. Granted I make thick core ASL's, but I would prefer the bulk of the materials I use, especially on the back, derive their strength from tensile properties rather than compressive. Otherwise you are moving the neutral plane toward the back of the Bow. Which is fine if your goal is to make a fiberglass bow with wood accents.

[Shredd]

Flem...  I feel there is something to be learned from your last post but I am not fully grasping it...  Could you explain it in more detail??

[Flem]

I'll give it a shot, but my apologies to any materials engineers.
I work off the premise that a Bow with more fibers in tension will have better cast. Tension being a dynamic property and compression more of a static one. Fibers in tension or compression want to return to a neutral state. Bow fibers in tension are being stretched, the fibers not being stretched are resisting that force. The stretching fibers are being pulled, the compressive fibers are essentially being crushed. So if the back of your bow contains a material with more compressive strength, it's going to move the neutral plane in that direction, which equates to less fibers pulling. Obviously there is much more than that to the properties involved here, but hopefully that explains what I was getting at.

[Mad Max]

That's just the way it is.
If you did not have fiber glass on the belly of the bow it would not work.
So the two working together is what makes it work.
The ratio's needed for both, Don' know 
Shredd needs to test more

[Shredd]

Tension almost always trumps compression when dealing with bow limbs therefore I would think that the neutral zone is naturally more toward the tension side of the limb...  I would also think that the closer that you can get the neutral zone to the tension side the better the performance that you should get out of a limb...

I am not sure That I agree with or understand some of your statements...  Like Mark said you cannot have one without the other in the bending of a limb...  I would think that they are both dynamic...  If you measure the thickness of a limb while it is flexed it gains about .005" that tells me that the compression side is moving, moving more than the tension side... If the tension side was moving more than the compression side the limb would be getting thinner...

 Flem -    "So if the back of your bow contains a material with more compressive strength, it's going to move the neutral plane in that direction, which equates to less fibers pulling."

   The back of the bow is under tension...  Why or how can it have more compressive strength??  Is it going to move the neutral plane toward the back or belly??  Less fibers pulling where?? the back or the belly??   I don't understand this statement at all...

   Maybe what you got in your head is not coming out into words that I can understand...  Or it could just be me...

[Flem]

"Tension almost always trumps compression when dealing with bow limbs therefore I would think that the neutral zone is naturally more toward the tension side of the limb...  I would also think that the closer that you can get the neutral zone to the tension side the better the performance that you should get out of a limb..."
Almost right, you want the neutral zone farther toward the belly, more material under tension.
I was not saying tension and compression are mutually exclusive. Of course all bows will have both properties. Since the original topic was Gordons vs Bearpaw, I was thinking along those lines. Because of the composition of the laminates, Gordon's is going to have more compressive strength and Bearpaw more tensile strength.
So if you are making a bow with Gordon's, the neutral plane is going to be closer to the back of the bow.
Which means less fibers or material in tension/pulling. Compressive forces are always directed inward, causing internal friction and hysteresis, which is lost energy. Of course their is lost energy under tension also. But...
If you could make two bows, each being exclusively under tension or compression, which would you choose? To take advantage of the best properties of each laminate, a bow with Bearpaw on the back and Gordon's on the belly would fit the bill.

[Roy from Pa]

All that is why I don't make bows wif glass in em.

[Crooked Stic]

Roy you so confused.    And I am getting close to. 

[Roy from Pa]

Mike, I'm betten these guys chewed the erasers off their pencils and ate that white glue in grade school and carried peanut butter and

jelly sandwiches in their lunch boxes:)

[Shredd]

Hmm...   So are you saying that a limb built with Bearpaw glass will have the neutral plane closer to the belly of the bow because the glass lams have more tensile strength??
 
 This should also apply to your theory...  Are you also saying that if you take an all wood self bow limb and backed it with glass that the neutral plane will be moved back even more towards the belly side??

[Flem]

Yes. The Bearpaw laminate, because of it's higher longitudinal fiber content is less likely to negate the tensional properties of the material adjacent to it. It comes down to friction. When we apply a force to a bow, we are distorting the materials. In the case of the material subject to tension, it's being elongated. The force is causing the material to move into an external space and assuming we are doing this in a gaseous environment, one that has less friction than the one it previously occupied. Conversely, the material subject to compressive forces is moving into an environment of increasing friction. So the question becomes which material is going to return to it's neutral, resting state faster? I'm working off the assumption the material under tension, subject to less friction, is going to return faster.

So if you increase the cross section of your bow the neutral plane will have to move one way or another, right? Which way that neutral plane shifts is going to be dependent on how much friction potential the added material has, or creates with the material it's in contact with.