Laminated limb construction

[snowplow]

Merry Christmas everybody!

I was thinking about laminated bows lately. When you laminate or glue two thin pieces of the same material together, when bent do they act stiffer than one piece of the total thickness of the material?

Is there a practical limit to lamination numbers or are their diminishing returns?

What can you tell me in general about laminations and how they act?

This is very interesting.

[nineworlds9]

I would say its not a matter of stiffness, but a matter of being easier to bend without breaking than the equivalent single thickness of material...then you combine layers to achieve the stiffness you want.  The layers also recover better...

I've said it before but I'll say it again, Vol.1 of the Traditional Bowyer's Bible would rock your world...

[snowplow]

I have to get that....

So are you saying that even when laminated, they tolerate bending more like they are still individuals? Meaning an equal thickness laminated bow will bend before breaking more?

[nineworlds9]

LOL...

Its not that it can bend more period but that it potentially bends and recovers more without any damage...

Here's another thought provoker for ya...

A selfbow is made from a single piece of wood...but wood is made up of multiple layers of growth...

T-minus -5 seconds to mind blown...

As Thulsa Doom proclaimed to Arnold in Conan the Barbarian,

"Contemplate this on the Tree of Woe..."

The actual bowyers will be along shortly I'm sure to explain with greater knowledge and veracity and perhaps clarify some of my muddy and unscientific musings...

[KenH]

Wood only supplies about 12% of the strength in a wood-fiberglass composite bow; while the glass is 88%.  

Several thin layers of wood are easier to bend into complex shapes like recurves.  
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Once glued the lam combination acts as a unit not as individual strands.

[KenH]

Wood only supplies about 12% of the strength in a wood-fiberglass composite bow; while the glass is 88%.  

Several thin layers of wood are easier to bend into complex shapes like recurves. Imagine trying to make these bends with a 1/4" or thicker stick 1-1/2" wide:
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Once glued the lam combination acts as a unit not as individual strands.

[damascusdave]

I have had two high end custom bows that have a single core lamination sandwiched between veneers...they are both very fast bows so the bowyers must know something

DDave

[JamesV]

For what it is worth: some of the best performing bow I have built have been a single wood lam with glass on both sides.

[Holm-Made]

A bow should perform similar with one lam or 4 as the distance between the glass is the same.

You could have issues with durability with a single lam as if there is a weak spot in the lam then the whole limb is weak.  Multiple lams are like a sheet of plywood and stronger, more durable.

Dave mentioned that he had a couple bows with a core lam and 2 veneers.  I'm guessing the veneers are not super thin like under .025.  They are probably thicker, thus he has a 3 lam bow.  Veneers count in your lamination stack, either way.  

In a bow with two veneers and one core, you would have 4 glue joints holding the limb together. (or more if you have more core lams, etc.)   In a bow with only one lam total you would only have 2 glue joints holding the limb together.  I'd rather distribute the stress among 4 or more glue joints myself.  

Also worth mentioning here is the bond between the glass to lam is not nearly as strong as the bond between lam to lam (wood to wood).

Just my ramblings on Christmas Eve as I'm home with a sick kid.
Chad

[7 Lakes]

Looking for a less expensive way to build a light weight bow for young teens, ladies and our aging population of archers I experimented extensively with a single Ash lamination on a 60" refelx/deflex form. They are nice shooters and so far... knock on wood there have been no durability problems. Maybe one day I'll break the chronograph out to make sure but to me they shoot every bit as hard as a 3-4 lam bow.

One thing I can tell you, after they are cut out and strung up the 4 lam bows fit back on the form better, the single lam bow takes a little string follow from the original form.

This info has only been applied to glass laminated bows.

[coldwinterlake]

I just received Bigfoot Sasquatch SS [email protected]" and there is only one core lam and power wedge at the root of the limb.
Actionboo core with VERY thin veneers under glass. This bow is a beast and shot some amazing numbers thru chrono. The bow is also very stable in every way. I'm waiting for Kirk's answer to this question....

[Orion]

Of course, action boo is multi laminated, it's just that the glue lines run in the opposite direction, perpendicular to the back/belly of the bow rather than parallel with it.

[**DONOTDELETE**]

Well.... some folks actually think the cores don't matter in a glass or composite backed bows, but i'm not one of them. Type of wood used and number of laminations can make a serious difference in some limb designs, and may not in others.

The bow Henry is referring to actually has  10 laminations in what appears to be a single core with two more veneer laminations over it. The grain configuration in the action wood makes a difference too.

Action wood with clear vertical grain adds not only strength to the limb, but helps with lateral stability.....especially in recurve limbs.... Core to glass ratio also effects how much the core plays a part in the whole matrix assembly.....

There really is a lot more to this stuff than meets the eye...

Bows with a single wood core are going to be more prone to string follow and will loose more poundage over the years than bows with more laminations. This has to do with compression characteristics of the wood....The fiberglass or carbon is only as strong as the core wood its glued to....If you think that wood doesn't compress inside the core and effect the backing, try putting carbon on the belly side of a bamboo core sometime....

btw....Be sure and wear a foot ball helmet and saftey glasses drawing that dude...

[Sixby]

Most of my bows have 7 laminations. Some of them in higher poundage to 10. Reason is that each lamination gets less stress on the wood fibers. I like to keep the laminations .055 or lower in the working area of the limb. This evenly distributes the work load and also allows the bowyer to build a higher performance design without overworking the laminations.
As to longevity it kind of depends on how much a bow is going to be shot. I want my bows to last as an heirloom and still be an extremely high performance bow.
I certainly agree with everything KIrk said about this subject/. Blown up enough experimental and prototype bows to know.
Anyone that builds all wood lam bows understands which woods work on the back and which work on the belly. Most of those principals are ignored in building glass lam and carbon lam bows and they should not be ignored.

God bless, Steve