Carbon in my longbow limbs

[Brad Isham]

I'm getting ready to lay up a r/d one piece longbow. I want to use two lams of carbon near the back just under clear glass and thin tiger maple; then two lams of action boo; then one belly lam of carbon before a tiger maple taper and clear glass. My concern is the belly carbon if it is necessary or should I put along with the other two at the back. The only thing I have heard from other bowyers is not to use carbon in the core. Please help guys! Thanks.

[Stagmitis]

So,
going from back to belly it would look like this?.....

1) Clear glass
2) Tiger maple lam
3) Carbon
4) Carbon
5) Action boo
6) Action boo
7) Carbon
8) Tiger maple Lam (only taper?)
9) Clear glass

0r,

1) Clear Glass
2) Tiger maple lam
3) Carbon
4) Carbon
5) Carbon
6) Action boo
7) Action boo
8) Tiger maple lam (only taper?)
9) Clear glass


For feedback it would be very helpfull to list the following.....

1) Thickness of each lamination
2) The total rate of taper in the bow limb as well as the rate of each lam.
3) The total stack at the fadeout
5) The total width at the fadeout
6) What pull weight are you hoping for?
7) Bow length
8) Noteworthy Design features; Is this a radical R/D design? How much reflex is there?

[Brad Isham]

I could lay it out either way... I'm trying to figure out which would be best. The bow is targeted to be 64"; the riser is curved so that laying horizontal the riser is 2 1/4" off the bench deflexing down to the bench about mid-limb then reflexing to the tips at 3" off of the bench. If I remember correctly I used a 12 foot radius when making the pattern. I start with 1 1/2 lams but usually work the bow to 1 1/4 " wide when finished and 1/2 to 5/8 wide at the tips. The lams as follows:

1) .04 clear glass parallel
2) .03 maple parallel
3) .02 carbon uni parallel
4) .02 carbon uni parallel
5) .04 action boo parallel
6) .05 action boo parallel
7) .02 carbon uni parallel
8) .10 maple taper @ .002 p/in.
9) .04 clear glass paralell

I'm hoping for weight in the mid sixties or slightly lower, I have a sanding planer and can taper the belly side carbon if necessary , I guess I'm wondering if it is better (the carbon) at the belly or glued along with the other two at the back.

Thanks for your time and your help Stagmitis.

[Peckerwood]

From my limited experience with carbon I do not think you will get any performance increases with your set up. I would eliminate the belly carbon. ( probably a waste of $). Are you aware that in addition to stack thickness carbon can increase # 5 plus per strip? I'm not trying to deter you from your build , I just don't want you to throw money away like i have in the past.

Bill

[Brad Isham]

Yes, that's why my main concern was the belly carb. If it's going to add stack then I'll leave it out or add it to the back. Thanks for the thoughts.

[BenBow]

IMHO from what little experience I've working with carbon I see 2 problems. 1st based on the total stack height I'd guess your draw weight will be close to 100# or more. 2nd using it on the back and belly places tremendous stress on the core and most likely will cause it to shear and fail. Carbon just doesn't want to compress. Frankly you only need one .030 carbon on the back and I wouldn't go over .030 on the glass either. .03 on the belly glass and no carbon. Better do some more research on carbon stiffness before you end up wasting a bunch of money.

[jess stuart]

I have only tried carbon once, I used on both the back and belly, the bow shot great but only lasted about 100 shots before it blew up.  It seems that I read that carbon does not stand up well on the back but will take the tension well on the back.  I am only going what I seem to recall and could very likely be totally wrong.

[tommy6]

I have heard that carbon should be used only in the belly, under the glass. I think I read it in
Traditional Bowyer, More Unnecessary Fun. Jack Harrison is the author, he used carbon in his wolf? longbows, I believe.

[BenBow]

Carbon has great tension qualities so it works great on the back (side away from the shooter) But hates to be compressed therefore overstressing the core. Takes a special design and material to handle it.

[tommy6]

Thats right benbow. By putting it under the fibreglass it actually acts as a backing to the belly fibreglass:

Back\\\\core\\\\carbon\\\\belly fibreglass

[Jesse Peltan]

snakeskin/ carbon/ core/ clear glass

[Stagmitis]

Benbow said;

"Takes a special design and material to handle it." Thats so true!

I found that I typically have to reduce my core stack by a minimum of 30% if I add carbon on the back and belly instead of glass to hit my desire #.

Carbon does HATE to compress so the design is "Crucial" if you place it in the belly. Assuming the design is sound then the next problem is to get a "smooth" draw. A reverse taper from tip to fadeout can work as well as a VERY thin laminate of .20 carbon or a combination of both......

Placing carbon on the back does very little in terms of adding #`s to the bow. The belly does that. The only thing you are saving with back carbon is some weight. Again, I notice a harsher draw and you can taper the carbon or go really thin!

My last bow had a.18 carbon paralell on the back with a .12 s-2 glass parrallel over that to protect the carbon. Belly was .40 e-glass.

You can try a carbon back and belly and still have an extra carbon strip to use on the back for another bow..Or, you can build 3 bows and use the carbon on the back...

Good luck!

[tommy6]

Another option is to decrease the stress on the core and belly by using a trapezoidal cross section, I believe 1:3 ratio (Back:Belly)