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Main Boards => The Bowyer's Bench => Topic started by: Shredd on October 20, 2019, 12:36:50 PM
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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...
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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.
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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.
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Yep, what monte said here, most of my bows are 45-50 and I add 5# to stack to come in...
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Kenny... Are saying that you add about .015" to the stack with Bearpaw to make the same weight as Gordons???
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Depends on the bow, stack change is different on different bows so I go with a 5 lb heavier than Gordon’s makes .
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My guess is a 45 bow with either glass will need a chrono to see the difference.
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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.
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Would be interesting to see the weight aspect between the two
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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.
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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??
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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.
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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 :dunno:
Shredd needs to test more :saywhat:
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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...
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"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.
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All that is why I don't make bows wif glass in em.
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Roy you so confused. :bigsmyl: And I am getting close to. :laughing:
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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:)
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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??
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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.
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You fellers are either purty dang smart, or some of the best BSers ever. :biglaugh: I'm keeping up with this logic for the most part. But then there's that part of me that says "Screw it, put a string on the dang thing and lets fling some arrow!!"
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Thats what happens when you eat PB&J while sniffing glue :knothead: :saywhat:
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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:)
I never had a lunch box.....carried my sandwich in my pocket ;)
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My head hurts :biglaugh: Flem how does that apply when say you put .030 on the back & .040 on the belly ?
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So assuming the core is homogenous and will not be a variable. if you increase the resistance to bending on the compression side, it would move the neutral plane toward the back of the bow, in contrast to a 40/40 or 40/30 scenario.
I want to be clear, I'm not saying that any of this would or would not be discernible, but it still exists as a physical reality. Does it matter? Maybe. Have to ask a Physicist for that answer. It's hard to ignore what you have come to know, unless it could be unknown because those erasers you ate somehow found their way into your brain. :bigsmyl:
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samich musta been in your hip pocket and it B flat :bigsmyl:
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Clem, AH NEVER MIND....
I thunk the glue dun did ya in...
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First I would like to correct one of my previous statements...
I said, "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 had it backwards... It should say, I would also think that the closer that you can get the neutral zone to the compression side the better the performance that you should get out of a limb"...
Flem... I think that you have got it backwards... Contrary to your statement... The more that you strengthen one side you move the neutral plane to that side... So if you increase the resistance to bending on the compression side, it would move the neutral plane toward the belly of the bow...
Here are some videos to prove my point... If you notice where the beam is more reinforced the neutral plane is closer to that side...
https://www.youtube.com/watch?v=asBW0Ojc0bY&t=54s
Go about 5:30 minutes into the video where the 'T' beam is and you will see where the neutral plane is closer to the stronger side...
https://www.youtube.com/watch?v=IyRZ0WIhCdU
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If I gotta worry about all this stuff, I'll quit making bows first...
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I don't think that's an completely accurate representation of the forces at play in a bow. Those examples incorporate 2 axes, we are dealing with one. Also you have to look at the total mass represented in those examples, not just the distance from each surface to the neutral plane. In that "T" cross section there is more mass on the compression side of the neutral plane. So because the compression side has been strengthen with more material, there is less total material in tension. We want more material in tension because it's more elastic, less friction.
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Your quote... "So assuming the core is homogenous and will not be a variable. if you increase the resistance to bending on the compression side, it would move the neutral plane toward the back of the bow"...
In the illustration they did exactly what you said... They increased the resistance on the compression side... Though it is a bit extreme it allows you to see where the neutral plane has moved... You are saying the complete opposite in your statement... And I fail see how this basic law of physics does not apply to a bow limb...
All I have left to say is that I have to respectfully disagree with you on the movement of the neutral plane due to the reinforcing or strengthening of the tension or compression side of a beam or bow limb...
For you guys in the peanut gallery... :clapper: I applaud you for your tasteless humor... :clapper: If you are having trouble comprehending something I think you need to come up with better jokes... I mean seriously we are talking about the inner workings of a bow limb... The low tech humor did not seem to apply... I think you need to step up your game a little... Because it begins to sound like BS... And I think BS is not needed when two men are trying to have a serious discussion... If you can't step up your game save your humor for where it might apply better... I am just a straight up guy telling it like it is... :shaka:
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My guess is a 45 bow with either glass will need a chrono to see the difference.
x2
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Thats why I said it's not an accurate representation of the forces at play in a bow. You are comparing a symmetrical cross section(1st example), which is what we work with on bows, to a non symmetrical one. Additional forces acting are on the cross section.
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Find a reputable source, other than your own opinion, anywhere on line that says that the neutral plane moves away from the more heavily reinforced side of of a beam, bow limb, ect... And I will be all ears... You make it sound like the laws of physics change when it comes to bow limbs...
Until then I am done with this discussion... Good Luck...
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So in the example you presented, they are working on baseline equations. So we need to pay attention to what is being said in addition to what is being illustrated. It's clearly stated at 5:18 "movement is negative, so tension at top and compression at bottom. Then when they shift to the non-symmetrical cross section, they clearly state, "same span and loading", so tension is still at the top and compression at the bottom.
Even still, I don't think that's the best example of what we are building.
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Lets keep it simple... Just find a source that supports your theory... No more opinions....
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The one you presented did just that Shredd. I could make the same request, since my assertion has been validated by the example you presented. Are you not willing to acknowledge that this statement is incorrect?
" In the illustration they did exactly what you said... They increased the resistance on the compression side... Though it is a bit extreme it allows you to see where the neutral plane has moved... You are saying the complete opposite in your statement... And I fail see how this basic law of physics does not apply to a bow limb..."
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All this neutral plane bow limb crap doesn't mean diddly dip without bringing into play tension wood, compression wood, and reaction wood characteristics.
What side of the tree did the limb materials derive from, the downhill side which is affected by gravity and is compressed already.
The uphill side which is already under tension from being stretched over from gravity.
Or the reaction sections of the wood which is chasing its tail between the compressed and tension actions on it.
Then ya got those wind shakes inside the wood.
For thousands of years, Caveman and Indians made bows from all natural wood.....
Then modern man decides to glue glass onto the wood and all hell broke loose.
I have no clue where the neutral plane is in my bows or if there even is such a thing in my bows.
All I know is my wood/boo bows are faster, quieter, and more accurate than those stupid glass bows:)
Go have a beer and relax.
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I dont know about the faster part but the rest is :laughing: :notworthy:
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First let me say that I am cool with the whole discussion other than the lame jokes...
Well said Roy... Thanks for joining the discussion and sharing your opinion and some valuable info instead of talking about sniffing glue and such... Nothing wrong with some tech talk... We are all in this for different reasons and have different approaches and we are not always gonna agree... But on this topic I agree to disagree and choose not to take it any further... I am glad I was involved in this discussion... I learned a very valuable point through my exploration on the topic... Which will better my understanding how the limbs work... Sorry if it was painful for some of yah all to listen in on the topic... But the jokes seem disrespectful when I am trying to talk some serious tech... If you all prefer I will will take my tech talk to private messaging next time... Just let me know... Or you all could just not tune into the thread...
Sounds like you need the beer... ;)
I prefer wine... :goldtooth:
PS I love this craft and a very passionate about it and my gig is about improving performance...
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:wavey:
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Well... I got a PM from Ol' Flem... We decided to put on the gloves and duke it out... Settle it like Gentlemen...
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I'm picturing another epic battle of Ideology
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Bad Roy :nono:
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According to my simple way of thinking, and it's served me well over the years, and with thousands of bows...
I've used both, and when I use the Bear paw glass I shoot for a draw weight about 6# more than I need. Saying, if I was making a bow with gordon's glass, and on a particular design, a .340" stack gave me a 50# bow, I would use that same .340" stack to get a 44# - 45# bow, of that same design with bear paw.
Also if you really need to hit a certain weight for one reason or another, and you decide to use a product you haven't used yet, be it carbon, a different sort of glass, or bamboo as opposed to wood, just make the stack around .005" - .010" thicker than you think you'll need. Because you can more easily make a bow that's too heavy lighter, but you can't make a bow that's too light heavier, without making it shorter, or gluing more glass on the back.