Trad Gang
Main Boards => The Bowyer's Bench => Topic started by: Bvas on June 04, 2018, 09:27:45 PM
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Lots of the guys here build glass bows and probably nearly as many build all wood bows. Each has there own reasons for their preference. And I think that’s great. Some sway towards simplicity, some towards performance.
As I enjoy reading about and looking over all types of trad bows, I’ve noticed that there is no huge performance difference between either type as a whole.
Most wood bow builders pay more attention to grain, species and overall quality of the wood going into their bows than most glass bow builders.
So.......If a glass bow builder used the same high quality wood in their bows, could the glass thickness be reduced to increase performance?
.040 glass is probably the most common for hunting weight bows. If quality wood is used, could .030 glass be used to improve performance, but still maintain the durability and reliability that glass gives us.
Just some food for thought. And before anyone says it. I know.....try it and tell us how it turns out. :biglaugh:
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"So.......If a glass bow builder used the same high quality wood in their bows, could the glass thickness be reduced to increase performance?"
Not really. The performance - power - of a glass bow basically comes from the distance separating to two pieces of glass; not so much what holds the 2 pieces of glass apart. About 88% of the power of a glass bow comes from the glass itself, and only about 12% from the wood between the glass; whereas all of the power of a wood-only bow comes from the kind and quality of the wood itself.
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"I’ve noticed that there is no huge performance difference between either type as a whole."...I'm sorry but I just don't know where you are getting this from. I know that there may be a few top self bowyers that can build a self bow to rival a glass bow of the same design, but for the most part, there is a pretty substantial performance difference between a self bow and a top glass recurve. I mean I would imagine there is an average of 30+ FPS difference between the two. That to me is substantial.
in regards to the glass differences, there is a ratio of glass to core that needs to be maintained. Too much glass makes the limbs physically heavy which robs performance. Too less glass and you start to lose the benefit of having it. Pretty much the standard is 040 for up to 60# bows and 050 for bows over 60#.
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From an all wood perspective, the quality of the wood doesn't really affect it's stiffness, which is where you get a certain draw weight per thickness. The stiffness may be a little more or less within the same species but there's no way you could tell that just by choosing quality bow wood with straight grain.
I was interested in the numbers so I just looked up the strength of bo-tuff fiberglass and compared it to some woods that I use in bow making. Fiberglass actually has a pretty average strength to weight ratio, with some woods like purple heart and bamboo actually having better ratios. But fiberglass is around 2 or 3 times stiffer and 10 times harder to break than most bow woods and has no memory. From what I gather looking at this data, the bow building community has found a perfect balance between the fiberglass handling the majority of the stresses in a bow while keeping it thin enough not to be too heavy to slow the bow down.
And there's a sub community of wood bow builders that focus on performance (mostly on PA), but I don't hear too many FG guys talk about performance. Is this something you guys talk about among yourselves or am I missing something? I personally would love to see some of the speeds you FG builders are getting and what designs are producing the best results.
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a couple years ago over on another site they were really pushing FG design to build fastest bows that they could. there is more research and discussion there than you can hardly absorb lol. basically it seems that FG bows are bottleneck performance wise limited mainly by materials. designs for FG bows have pretty much maxed out until some breakthrough are made in new materials. selfbows however are highly dependent on the craftsmanship. not like FG which is more scientific formula based
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Ken-
I'm not disputing your numbers, but where did you come up with the 88%/12% ratio? And what percentage of glass is used in the stack to get this ratio?
Tim-
I was referencing more on the side of wood laminated bows.
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I was gonna say I got that 88/12 from TBB, but I'm not sure, now. Maybe it was one of the books in The Archery Library. Ben Hunt? Sorry -- Senior Moment...
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try it and tell us how it turns out. :laughing:
Use the best you can on either type. No idea on how much work the glass does in percentage.
Hmmmm. .. if the core only spaces the glass, maybe make a solid glass limb and test it out? Bet the same stack would produce more #s :o :)
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Ken, I remember that from one of the TBB volumes. Probably by Baker. It pertained to all wood bows I think. It's probably applicable to FG bows too.
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With my limited exsperience I have always thought the mass of the core was the most important for performance , but I think there is a growing trend in the self bow world to post chrony numbers on fresh bows in my exsperience there can be as much as a 12 fps drop after breaking in a self bow ,here is a example the osage bow below was shooting with a 6 strand FF plus string fresh ,arrow 20 ,180-181 fps 530 grain arrow , 400 arrows later 10 strand string 172 fps 530 grain so arrow 20 as good as glass, arrow 400 not so much...lol the glass bow 16 strand D97 550 grain topping 187fps when I get a good release all of my self hunting bows this year are in the low 170 fps for my limited skills ,the only natural bows that I have seen that keep up with glass are composite horn bows !
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Wood bows generally lose 3 to 5 pounds of weight after 400 arrows.
Glass bows do not.
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That osage bow didnt loose any weight sense during tiller it has actually gained weight by 1 lb sense I made it the stave was only off the stump 1 1/2 years every osage bow I have made gained weight from younger staves one I had to re tiller it was to heavy for me !
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Cool, then it must be the larger strand string then?
Or your getting older and can't pull it back as far?
:laughing:
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LOL... :biglaugh:
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You guys must be talking to Mrs Yellowood :biglaugh:
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Yup..
Cause she's the only one smart enuff to listen..
:laughing:
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Maybe my original post was a little vague. That and you guys just like to take things right off topic. :laughing:
My main point is.......Is there an optimal glass thickness? And knowing that glass is usually the heaviest component, can this glass thickness be reduced if high quality material is used as “spacers”?
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NO
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Brad I have had the same questions as you and have looked for books on glass bow designs , not a lot ,I have found Jack Harrisons probably the most informitive but I have read tons on natural material designs of laminate bows, Adam Karpowicz book on composite bows , that might cross link some,he goes into great detail of design and limb thickness ratios but it seems there is always a trade off between stability & performance I have often thought about experimenting with differnt back/belly glass dimensions sorta a trapping effect or the guys using foam cores seem to get a bit more performance sorry for going off topic I thought you where asking about performance differences between self/glass to !
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Sorry guys. Didn’t mean to confuse you about the selfbows.
I was comparing laminated bows. With and without fiberglass.
Let me ask the question in a different way.
If you have an all wood trilam design with outstanding performance ....Would it improve if you were to add very thin fiberglass to it? Say .020 glass?
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Heck dude, then it would be ah gwass bow..
:laughing:
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It probably depends on the design and over all mass of it ,most woods are stronger in tension then compression wonder how a glass belly sinew or hickory backed maple core would work ? The high compression belly allowing high reflex design to stay that way, probably great especially if you drum sanded the belly lam 0.015 or so , ok back on topic 😝 But your OP got me thinking if guys that are making HH follow bows make them on a strait form and allow the set of the lams to create the follow in the bow then obviously the lams are taking some set and doing some work so lighter stronger lams I would think would improve performance, weight/work ratio aka (mass) I have herd maple core glass bows tend to have the best performance , but I dont know I have only made 1 glass bow its just like most things with bow theory you really never know tell you build it !