Primitive Archer
Main Discussion Area => Around the Campfire => Topic started by: tkdHayk on January 07, 2017, 02:16:31 pm
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Unstrung: http://imgur.com/csOL7aw
Strung: http://imgur.com/jVpaNFp
4-5 layers of sinew, red oak board core. Bows is 2 inches at the widest point and tapers to the narrowness of my finger. Bow is in progress. All I have to do is add a belly. I was planning on using horn but couldn't find any so I decided to try fiberglass for the first time. Not sure how well this will work out as it is a curious combination. I'm mostly concerned that the bow will be too light even after the fiberglass belly is glued up. I have pre-tillered the bow before adding fiberglass since I don't want to have to remove lots of material once it is glued up.
I want the the recurves to have extra support as well, so Ill have to heat treat the fiberglass into a new shape, then glue it on. Is this possible/safe? i was planning on using a heat gun and bending it by hand. can fiberglass be molded with heat?
Is fiberglass supposed to be stiffer than wood for its weight? the black fiberglass lamination I got from an archery supply store doesnt seem stiff at all. how much weight do you think it would add to my bow? its 0.04' thick. Thickness with fiberglass held up to the bow: http://imgur.com/rF4VObJ
P.S. is there an easier way to post photos on here other than linking to a 3rd party image hosting site like imgur?
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This is a primitive forum. You'll have better luck asking that question on a different site. Why not just a wood belly? Cheers- Brendan
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Beautifull bow so far.
I don't think the FG is gonna do anything mechanicaly or astheticaly for it.
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I guess fg would be too stiff. what about "toxhorn"?...
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Sorry no f- word allowed
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Move it to the campfire page. No glass fibers on the bow page.
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Is fiberglass supposed to be stiffer than wood for its weight? the black fiberglass lamination I got from an archery supply store doesnt seem stiff at all.
Yes, stiffer than everything else on our bow. Stiffness meaning a higher tensile and compressive strength. In a .04 thickness it seems floppy, but if it was half the thickness of the limb, you would see the "stiffness". I will bet that your choice of materials will also show you what sinew can do, as the belly might "overpower" the back, or at least make the sinew elongate and work more than it usually would, on wood/sinew bow without the f.ff..ff.... (I cant say it here, without ruffling feathers)
BTW, challenging design, and nice job so far.
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This is a primitive forum. You'll have better luck asking that question on a different site. Why not just a wood belly? Cheers- Brendan
I know, I wanted horn because it is stiffer against compression than wood and I could push the bow further than with wood only (longer draw length, more stored energy). because the bow is reflexed, I wasn't sure if wood would hold up at my desired 30 inch draw length. what wood would you recommend? bamboo?
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I guess fg would be too stiff. what about "toxhorn"?...
Why would it be "too stiff"? I have 5 payers of sinew so I don't see the back failing. Is fiberglass supposed to be stiffer than wood?
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Is fiberglass supposed to be stiffer than wood for its weight? the black fiberglass lamination I got from an archery supply store doesnt seem stiff at all.
Yes, stiffer than everything else on our bow. Stiffness meaning a higher tensile and compressive strength. In a .04 thickness it seems floppy, but if it was half the thickness of the limb, you would see the "stiffness". I will bet that your choice of materials will also show you what sinew can do, as the belly might "overpower" the back, or at least make the sinew elongate and work more than it usually would, on wood/sinew bow without the f.ff..ff.... (I cant say it here, without ruffling feathers)
BTW, challenging design, and nice job so far.
Thank you. I think I may have to add more than one layer of fiberglass because the bow is much too light at this point. I'm willing to do that, but fiberglass seems really heave for the amount of stored energy it would add, compared to wood. Is there a drawback to using too much FG in a bow? for example, If i made a bow out of 100% FG, would be physically heavier or lighter than a wooden bow of the same design and draw weight? there must be a reaosn that FB laminated bows have wood in the middle. I'm assuming that wood gives more stiffness for its weight, while FG gives more stability and allows more extreme designs. Otherwise, we would see more bows made 100% from FG. Right?
I'm still not sure about adding FG to this bow until i make sure that FG offers more stiffness for its weight. i want my bows as physically light as possible while storing as much potential energy as possible. I didn't want to use wood on the belly because the bow is reflexed, so i wasnt sure if wood would hold up at my desired 30" draw length. Horn or fiberglass seem to be the only viable solutions for this design since they resist compression better than wood (supposedly).
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Horn is stiffer than wood?
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Horn is stiffer than wood?
it resists compressive forces better than wood as far as I understand, and prevents the belly from crumpling under compressive forces.
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What types of wood do you have access to and how long is the bow? You might as well ditch the glass idea if you want more feedback on here.
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What types of wood do you have access to and how long is the bow? You might as well ditch the glass idea if you want more feedback on here.
the bow is around 60 inches and has a somewhat hinged limb design with the inner midlimbs doing most of the work as you can see in the photo.
I have access to hickory and bamboo "backing strips". But my goal is to make the best/fastest bow possible, so whatever material works better, Ill use it, even if its FG. Form my understanding, wood is stiffer than fiberglass for its weight, but breaks more easily. So ideally, i should have a wood core, sinew backing, and fiberglass or Horn belly. Do you think bamboo or hickory could really do the trick for the belly? keep in mind this bow is reflexed and will be drawn to 30 inches.
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Depending on the total length of the bow and the desired draw weight, heat treated bamboo might work. As fiberglass is not allowed in this forum for philosophical reasons, you really need to try harder to use bamboo at all cost. If you only have bamboo backing strips, you might have to use more than one layer of bamboo. Good luck.
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Hopefully this will be moved to another section soon..
About stiffness- forget about stiffness. Bow building is all about compression and tension. Sinew has no stiffness, yet it is used on the back because it resists tension. The bow's belly is under compression- so use a material that resists compression (wood, horn, FG). Fiberglass is very resistant to compression, while sinew is quite stretchy- therefore if you put on a FG belly, the sinew will stretch way more than the FG compresses (this is what's meant by "overpowering the back).
The reason wood is used between FG laminations is that it's lighter than FG. Whatever material you have in the center of a bow does almost nothing- it's just there to hold the back and belly apart- FG would work for this, but the added mass would slow the bow.
The reason your FG lam doesn't feel stiff is because it's thin. If you could slice it into two strips that are even thinner and then put a wood core between them, it would feel very stiff. Even if this core was made of dry pasta, it would still feel the same.
You ask- "would wood work for the belly? Yes, of course- bows have been made this way for thousands of years.
If you want the best and fastest bow, it doesn't matter if you build it from wood, horn, sinew or FG- it's all about design. The best FG bows outperform wood bows by only a tiny amount.
If I were you, I'd try to laminate a hickory or osage strip to the belly- this will be quite difficult to achieve a good glue line because the bow is mostly built already.
Next time, I recommend using a method and design that has been proven successful. Once you get a few bows under your belt, you can try something radical.
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the term "stiffness" is being used with two different definitions in this thread, and hopefully aarons explanation helps to point out the difference.
The reason your FG lam doesn't feel stiff is because it's thin.
and the same can be reasoned for the bow it's self, and that is why a belly of bamboo may be the best recommendation, it adds thickness faster than the fiberglass would with less weight
I want the the recurves to have extra support as well, so Ill have to heat treat the fiberglass into a new shape, then glue it on. Is this possible/safe? i was planning on using a heat gun and bending it by hand. can fiberglass be molded with heat?
No, not moldable after the resin has cured, but if you're minds set on fiberglass, a fresh layup with a few strands of roving, set in epoxy or polyester would be possible. However, you should realize that you may not get the performance you seek, as most of the work would still be happening in the sinew......
which ever way you go, the results will be informative at least and the sinew can be salvaged if you choose to use it in a more traditional design.
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You can get Asiatic buffalo horn from James Parker at Huntworthyproductions. He usually has whole horns or slats for horn bow bellies. James is a sponsor here on PA.