Whats this talk about foam in limb cores

[Cody Roiter]

Hello guys, I may be reading something wrong but what is foam in limb cores. what dose it do or made of and why is it used....
Thank's
Cody

[Bob Sarrels]

It is very hard foam that is actually cut and ground into core lams for bows.  Have not tried it in any of my bows yet but have heard good things about.  Might give it a try but I am still stuck on boo.

[katman]

According to my readings the foam core limb has two advantages, first it is more temperature stable, that is to say poundage is not affected as much shooting in extreme variances of temperature (important to long range shooting like Fita Olympic).Second it is of lighter weight than wood cores so this should make a faster limb. Some have reported foam core to be a little louder than wood core.

[KentuckyTJ]

Talked with Bob Morrison about them and he is getting 2 ft/sec speed increases with foam cores over boo. He shipped me a set of foam limbs and they are lighter. They are smoother to draw and quieter. He also just finished testing on foam cored limbs covered with carbon veneers and he is getting a 4 ft/sec increase in speed over boo limbs.

[owlbait]

Sorry for posting irrelevant information, i am a  

[Dartwick]

The most quantifiable difference is its lighter so you have more efficient energy transfer from the bow to the arrow.

[KrEn]

Foam core limbs give from 0 (or negative) to 2-3 fps of speed gain. This i have from several written sources, also talked to Sid at Border Archery.
Generally foam core cost ~200$ over maple cores, or maybe 150$ over boo.

The difference in feel drawing must be extremely slight, on release shock is possibly reduced due to lower mass.

However, the reason people are paying for this is 70 and 90m FITA competition. Your # of sight clicks is far more constant on foam limbs. This makes a difference, when you shoot a day full from morning till evening + finals @3 different (long) distances. Come sun, come rain, you hit in the same place. On wood you must compensate for temperature.
This is what the FITA fellows says. What Sid Ball said, was it was no improvement whatsoever defending the cost if you are not sight shooting @ long distance.

Now on factory ILF limbs the price diff is not what it is on custom limbs. The fastest ILF limbs available are still wood, Samick Masters I hear.


K

[O.L. Adcock]

K, your's and Sid's conclusions are closer to correct then any expresed so far!    Much is marketing of properties that can't be measured by the ave***e archer, therefore can't be proven. An example, I had some foam cores used by Hoyt, weighing them, they weighed the same per square inch as red elm. Folks only think they are light cause they call it "foam". Many of the foam limbs are "light" but that's due to the carbon, not the foam....O.L.

[jack benson]

Cody...

Ron and Gregg had a foam core/carbon limb'd Shrew in Kalamazoo. Give Ron or Gregg a call and get their input.

Catch you around...

jack (Smith's Dad)

[KrEn]

OL, i'll elaborate, since ive studied this in my process to buy myself superfast recurve limbs, that are ALSO all the other things, result is i have sold and traded and do not even own a complete modern material bow right now
   

I have a pair of Hoyt 900CX foam limbs right here, i havent weighed them. But i have chroned arrows shot w them, on a Hoyt Helix riser.
They are no faster than my own Winacts, and significantly slower than a a pair of old FX-limbs, both wood core.

However, the new Hoyts ARE smoother at the end of the draw, and they have more torsion resistance, and different tiller. They are shot full of crossweave and doodahs to make the shot more forgiving to the archers errors. Such as
- bad release
- inconsistent draw
- inconsistent hand placement
- etc.

Point is, you cannot compare directly unless you know what else is in the limb, to achieve other things than speed.
Also modern tiller is different, as both better machining makes other tapers than oldfashioned "straight taper" possible, as well as more accurate, newfound (crossweave)  torsion stability has also given the possibility to make limbs narrower, and new tiller shapes are seen as well. Do not hang everything on "foam", as in all bowmaking perfect tiller is king.

The main point is, as said before:
*Syntactic foam does not vary in draw weight nor cast at anywhere near the extent wood does - mainly in temperature changes.
Even this effect is small, but noticeable, at 70 and 90m.

Moisture resistance  have been mentioned, but the wood in bows are usually thoroughly sealed anyway.

K


*Since the material in the foam that does the work
(the work is to do no work..) is glass usually and sometimes mixed w/ carbon or glass fiber, some (Border) has a foam that supposedly is purely polymer,"strenght" is normally proportional to weight anyway.

The term syntactic comes from tha fact that the "bubbles" in the foam are "made", they ar fabricated from a (usually) different material than the continuous phase. The original syntactic foam was used in the oil industri in the 60s and was glass spheres in epoxy.

[bjordnolf]

Do you have info on the weight of the foam and or compression strength in psi?
thanks

[KrEn]

"what foam", the beauty of syntactid foam is it can be tailored to the specific needs.

Since wood is strong enough, i would GUESS the foam used in bows have strenght properties similar to wood, perhaps somewhat less tension strenght and somewhat higher compression. More isotropic than wood.
If you want it stronger, you would need heavier, so no one would use stronger than necessary, and wood is just about as strong as neccesary.

For the current bow designs, that is.

Again, i dont KNOW this, im ass-u-me-eng(ineer)

K

[KrEn]

This is all so old fashioned, eh,

United States Patent 4819608 was filed on August 24. 1987 by Earl Hoyt et al.

K

[Red Boar]

Great information, Krister!    

[Pluck Yew]

Cody..  :eek:  ...
Shawn...

[Cody Roiter]

Thnaks guys, I have never seen any bows that had it.. I think I will stay with all wood core now... In tell I get better at bow making....

thanks for the info

[Hattrick]

QUESTION.... if a bowyer is making his limbs out wood an then makes the same limb with foam an carbon an it shoots say 4ft per sec faster at the same poundage to me that justifies. If not than why? It seems to me that this would answer`s it

[artifaker1]

I was just down at the local trad archery store and they had several of Herb Melands pronghorns there. They had one with the foam core glass backed limbs (no carbon) and it was noticeably lighter in the hand than the other pronghorn bows. The foam was a gray color. It was really noticeable to anyone. They said they had got the chono out and it was keeping up with the wood core pronghorns. They also had one with solid glass limbs and it was heavier and had a little shock. And it was 60", the others were 62" I believe.
I don't doubt the information above in the least but I wonder what is going on with that??????
Also this is a great subject, just couldn't stay out of it.

[O.L. Adcock]

Hatrick, "QUESTION.... if a bowyer is making his limbs out wood an then makes the same limb with foam an carbon an it shoots say 4ft per sec faster at the same poundage to me that justifies. If not than why? It seems to me that this would answer`s it"

Yep, my feelings too...But for some reason the makers won't hand one (or a pair, one with, one without)to Norb or Blacky to prove it.....O.L.

[Hattrick]

It would be interesting to compare apples to apples, i have a Morrison with carbon- foam limbs. Its fast an noticeably smoother than any wood bows i`ve shot, is it the fastest don`t know, its long bow an feels as fast as any recurves i have. But  its defenitly the smoothest bow i nave shot