laminates grain direction?

[DonLee]

is there a preferred grain for laminates when making a glass bow? im thinking of a ASL bow, but recurve really as well.  quarter sawn vs plain sawn ? has anyone keept a record of not only thicknes but grain direction? Im thinking yes.

[Crooked Stic]

Edge grain for core will be best such as vertical laminated bamboo.as far as veneers go being so thin crazy grain gonna look better.

[Kirkll]

On an ASL design you would be better with vertical grain rather than flat sawn material for the highest strength in tension.


But..... I just spent a couple hours on the phone with Alan Case the other day talking about heavy bows and compression issues ive been having. He told me that he did some compression testing using flat grain maple and pushed it till it blew, then put it under a microscope to see the difference from vertical grain maple.

Believe it or not, the flat grain held up to extreme compression much better than vertical grain.  He said he has a test going right now using thin book matched flat grain lams that are stacked 180 degrees so the opposing grains are equalized. He expects much higher compression ratings with the two thin lams and an epoxy joint than a thicker maple lam.     Food for thought on that subject...   Kirk

[Crooked Stic]

You may be right about maple. If that's what you use for core. That the guy who concentrates on flight bows.

[Kirkll]

Yup…. Alan has been chasing the world record for 15 years now. shooting arrows over a mile is pretty incredible. All you need to do is get 110 grain arrows shooting about 800 fps, and be able to draw 300#.

Here is an article….


https://www.opb.org/article/2024/11/16/beaverton-mechanical-engineer-archer-chases-record-longest-arrow-shot/

[Kirkll]

Rock hard maple has been an industry standard for many years due to its longevity characteristics. For mass weight to strength properties, you will be hard pressed to find anything better in the natural wood class.

With popular draw weights between 50-70# draw you can realistically use pretty much anything for core wood with fiberglass backing and have it hold up well. Especially building long bows…. 

But once you get into building high performance static tip recurves, those limbs are storing energy in a much shorter portion of the limb, and the dynamics going on in the core of the limbs are much more extreme. Once you get past 70# it’s the compression of the core next to your belly glass that fails. Using thicker glass is the ticket on heavy bows.  Using carbon on the belly typically shears the bond to wood cores even quicker. I’ve tested using carbon over glass before and it’s still tough to get it to hold up long…. The best longevity I’ve come up with so far, and highest compression rating is using thinner maple lams on the belly side.

But I’ve never tried a flat grain laminated approach before, but it makes sense that two .030 lams with epoxy would be stronger than an .060 wood lam by itself.


I’m currently testing this Fossilized bamboo for extreme compression properties on the belly side  in hopes of getting some 80-115# limbs to hold up longer. These guys drawing them from 29.5 to 31.5” isn’t making it easier ta boot…. I’m going to mix in some carbon in the core too on the really heavy set. I’m still using 050 glass on the belly though.

Who knows… I may come up with a suitable flight bow before it’s all said and done.

Kirk