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Carbon limb stack

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Carbon limb stack

Postby Cutty » Sat Dec 01, 2007 11:12 am

So, I've been following that double carbon limb thread, and following Gilnockie's carbon bow building for a couple years now, and the one thing I can't understand for the life of me is why bowyers would want to reduce the height of their stack to drop draw weight when using carbon?

To me, that's just killing yourself in two ways...the thinner your stack, the less stiffness you are getting out of your carbon-- that's one of the reasons it's used on the outside of limbs (same goes for glass, by the way). Plus, the thinner your stack, the less torsional stability you're going to have, right?

Not to mention, the thinner your stack, the larger percentage of core material you're going to have on the neutral axis, where it's just weight, just slowing you down.

Now, I'm pretty sure the reason guys do this is because they're scared to go too thin on their carbon, thinking about belly failures. But, the one thing that Gilnockie says that has always resonated with me is he's found belly failures weren't the carbon's fault, but the design's fault.

Back to the bamboo rod tapers again-- with bamboo rods, the conventional "step and dip" taper, that doesn't progress continuiously, but incrementally, leave a rod with a whole bunch of "hinges," which even though they're not easily seen, cause a bunch of points that get stressed a lot more.

You with me?

So, in a nutshell, the more R/D you use in your carbon limb, the more hinges you're going to have, because the stiffness of carbon is going to magnify any design flaws.

And why do you need R/D in a limb?

To add stiffness, while saving weight.

But you can get more stiffness with a thicker stack-- IF you can reduce weight from your stack, right?

So, why are bowyers using actionboo as core material, with carbon? That stuff's heavy-- and the 'boo fibers have been compressed by the laminating process, causing a loss of strength and elasticity over natural 'boo. Plus, there are a whole bunch of lesser density woods that seem a lot more promising for core materials, like Poplar, for example. Or beech and spruce...which is typically used together.
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Re: Carbon limb stack

Postby tjdeerslayer37 » Sat Dec 01, 2007 12:23 pm

The reason i thought bowyers reduced the thickness of their stack was because the carbon is so much stronger as far as draw weight that they needed less material to get their target draw. thats just what i thought and i might be completely wrong.

i thought actionboo was quite light? but at the same time isnt boo really fast and super strong? i thought thats why they were using it is because it can keep up with the strength and speed of the carbon.

this is just what i have goin through my brain so who knows i might be brainwashed. :D
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Re: Carbon limb stack

Postby Gino Bruno » Sun Dec 02, 2007 1:49 am

pete- as far as stability goes, there is a point of deminishing returns...... for the most part, even with carbon, a longbow limb will be plenty thick enough to offer far more torsional stablity than even the best ILF limbs...... now, exclusive to longbows, nearly all of them including even radical hybrids like mine have a cord length that is not prone to cause an unstable limb in the torsion department..... what i mean is, take a static tip recurve, when the bow is drawn, the "curve" of the limb is still .......... well .............. curved....... this acts as a lever that easily magnifies release errors because that lever gives a mechanical advantage over a limb that is straight when torque is induced from the string. so imagine a plane where the majority of the limb is at when drawn, any limb that has some or part of the outboard portion of the limb running away from the plane in relationship to the direction that is being drawn is inherently going to cause some instablity...... nearly all longbows and hybrids don't have this issue when drawn. so really, torsional stability is seldom ever an issue........ vertical stability is another story and that is a design flaw if a bow does suffer from that.

with some designs, most core materials can not handle the massive stresses that are applied on them by the carbon..... thus, it is manditory to reduce the stack just to get the cores to hold together. also, in those designs, if the core is not reduced, you will have a bow that even the mighty TJ Craig could not draw :twisted: . but i think a lot of it has to do with some bowyers understanding of the material as well as the multitude of layups that exist with carbon..... not too many guys in our ranks have truly researched carbon and/or the industries that are using it to it's potential.


as far as the neutral axis goes...... isn't that just a very finite line?....... i think guys way over think this one.

hinges are definate points that are getting stressed. for instance, look at a bow that has piss poor fades, or heavy string groove overlays that don't finely taper out...... if the bow is built corectly, hinging should never be an issue...... ever, if so, the guy has a serious issue with his taper sleds or he flat out needs to redesign his bow :D


TJ-
"The reason i thought bowyers reduced the thickness of their stack was because the carbon is so much stronger as far as draw weight that they needed less material to get their target draw. thats just what i thought and i might be completely wrong."

you are exactly right....... the reason that the all carbon limbs perform higher than the glass limbs has little to do with the carbon itself per say, but in the physical weight savings that are gained in the limbs by reducing the core material due to carbon's stiffness..... very little has to do with it's increased recovery rates.

actionboo is actually heavy as a limb wood (grass). pete is right, it is highly compressed which makes it less desirable than the natural stuff because of the increased weight..... as far as strength goes, think of it this way, when it is compressed during manufacturing, it is being crushed........ therefore some of the fibers have been destroyed...... the issue with actionboo and the reason it is really popular is that it is readily available, it is super cheap (if you cut and grind it yourself from bamboo flooring), and it is fairly consistent........ i have weighed the stuff and it is actually slighly heavier than actionwood (the real stuff that is made from maple, not the new yellow birch shhhhhhhh........tuff :D ). but maple actionwood is much stronger and every bit as consistent..... if not more so. my favorite wood combos are walnut with a belly lam of hickory or actionwood in my carbon hybrid...... or padauk with a belly lam of hickory or actionwood....... the fastest hybrid i have made to date was two lams of padauk and one lam of actionwood........ in recurves, it is tough to beat a laminated walnut( "actionnut" if you will).... or just a plain old straight grained board of walnut....... rule of thumb for walnut as well as padauk is look for the lightest colored board possible...... it will usually be the lightest in physical weight as well. just don't use padauk as a belly lam...... it's shear strength is not up to par in a carbon limb.
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Re: Carbon limb stack

Postby Cutty » Sun Dec 02, 2007 7:44 pm

Now we're talking, Gino.

By the way, one fo the first things you can see about carbon in the Trad Bow industry is NOT ALL CARBON IS THE SAME!!

Can't even stress that enough, no pun intended. A lot of the stuff I see offered, say from Gordon's, well, I really doubt if you're going to gain much, if anything in performance over a high quality S Glass. And in a recurve, DEFINITELY not worth the money.
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Re: Carbon limb stack

Postby Hank » Sun Dec 02, 2007 8:42 pm

Actionnut -- what a great pirate core :)

I have a hardwoods place about 45 min from here in Illinois. They harvest, cut and dry hardwoods from the area. Guess I better check out the maple and the walnut.
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Re: Carbon limb stack

Postby Hornseeker » Mon Dec 03, 2007 3:27 pm

I dont think a guy can go wrong using maple. I dont use it much, but it is Well proven, is very strong, unfortunately...a little heavy.

I use red elm, walnut and juniper as much as possible. I have a guy asking for action boo limbs right now. He insists its the best, and thats what he wants. I tried to tell him he cant tell the diff between it and my elm...but he's paying the bills...sooooo...

So...why not use a thicker core, like Pete is saying, and a super thin carbon lam... Like 015???

I am LOVING using my 030's with a single 002 taper, a paralell and a tip wedge...

E
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