Why do we use so many laminations in glass bows?

[insttech1]

This question is for longbows and recurves, but if separate answers apply, I'm all ears...

Apart from the aesthetics of veneers, why do we use 3, 4, 5, and sometimes even 6 or 7 lam's in a glass bow configuration?

If a butt thickness needs to be .240", for example, why are we using 4 lam's of .060, and not two lams of .120"?

I know that the configuration and layup of parallel-vs-tapers has a huge impact on shooting performance, but some bowyers are going taper, parallel, and then reverse taper in the same limb layup.  Then, at least mathematically, they're so close to back to parallel that it can't even be determined with a micrometer what is supposed to be where without looking at the glue lines.

When I spoke to Elmont Bingham personally regarding the tapers and formula for a bow I was making, I asked about which way to layup the limb, as far as taper on the back or the belly, and the response was "it just doesn't matter".

I hate to say it, but in extroardinarily simple terms, if a limb need to be .240 at the butt, and tapered at the tip, what is the true benefit of 4 lams in that setup, and not one properly-shaped lam for 1/3 the price?

What about kids bows?  How 'bout just using a .125" lam for 56" kids longbows, instead of doubling or triping the price by buying at least two, and sometimes three lams just to hit 20 or 25 lbs?

Just food for thought!
Thanks!
Marc

[RAU]

ive wondered the same. I hope someone speaks up. I really believe alot of the formulas out there are written to sell us 3 to 6 pairs of lams per bow. That comes out to a substatntial chunk of change for someone like myself who would like to build a bunch of bows and really learn the craft. Especially when you are considering buying glass, glue, riser blocks,phenolic,finnish etc. etc.  Maybe im totally wrong, and seversal pairs as oposed to 2 pair really is beneficial. I just cant see how, but as i stated above, im still learning. I cant deny the fact that several contrasting lams in a bow sure does look nice tho.

[vermonster13]

Seems in some cases multiple lams would strengthen the limb when bent as opposed to one lam being bent. Less likely to break. A tri-lam all natural bow seems a lot tougher than a selfbow.

[Jeff Strubberg]

Two reasons.  One, the glue line is stronger than the wood.  More glue lines = more strength without more material.

Two, it would be all but impossible to get a .250 lamination to conform to a highly curved bow form without the use of steam or serious heat.  Multiple thin laminations bend very easily because then can slide past each other before the glue cures.

[shaft slinger]

Jeff's got a point there,BUT some of the best bows ever built had just one lam. the groves bows come to mind and there are others too  

[ONE SHOT]

Multiple wood laminations are more homogenious, stronger, have less chance of taking a set when left strung than lets say a single thick .250" piece of Action Bamboo or any other piece of wood, add the "F" glass on the Back and Belly, and you more than likely wouldn't even be able to come too your full draw length.

The Bow would have a sub-par cast to the arrow. The multiple wood laminations along with the "F" Glass give the limbs the snappyness that is required to store the ENERGY in the limbs.

Same principle applies to a piece of laminated plywood versus a single board, the Plywood is much stronger than the board, this is also TRUE in limb stack-ups.

Remmeber the old saying about an all wood Bow is eight tenths broken before it is ever shot. (Some food for Thought)....ONE SHOT...          :D

[traditional beagle]

I use 2 lams and 2 strips of glass. Don't see a bit of difference in performance. I don't buy the glue line theory. But some will not agree with me. I don't think a 3/4" piece of plywood is as strong as a 3/4" piece of locust or oak or hickory. Maybe pine. I like to argue. :>)

[Jason Jelinek]

With many laminations you can get the limbs to fit the form with less pressure (less stress in the glue lines too).

Also if I want a limb that is .350 thick at the butt with .008"/" taper and you want a limb that is .350 with .006"/" taper, 2 separate custom limb pairs need to be made.  I can also build those limbs by 4 .002"/" lams of the necessary butt thicknesses to get the 0.35 needed, and you can buy 2 .002"/" lams and 2 .001"/" lams.

Basically its easier to create many different options and let the bowyer pick the lamination combinations to get the limb they want instead of custom making a single lamination for each bow.

Jason

[Jeff Strubberg]

I don't buy the glue line theory.

Buy it or not, it's simple science.  Try peeling apart a laminated limb, let us know which gives first.

[Orion]

Bamboo varies in density from the inside to the outside of the stalk, becoming stronger, more durable and snappier toward the outside.  Thus, more thinner laminations cut from near the outside of the stalk will yield more performance than the same thickness of fewer but thicker laminations.  Hope that makes sense.  This only applies to bamboo though, not wood laminations.  And even with bamboo, the difference isn't usually very much unless just one or two very thick laminations are used.

[TNstickn]

More layers equals more stiffness. Not sure how that equates with strength. Think about form building and lvls vs plywood vs a 2x12. more rigid, no warp, more layers.

[Shaun]

Many older factory bows seem to have two .002 tapers and one parallel in the middle. The draw weight could be varied by changing the thickness of the parallel without any other changes.

Layers make a more homogenous product with more stable and predictable properties. Wood is a non uniform material and layering helps even out diferences. Hard maple is one of the more homogenous woods and I believe that is one of the reasons it was often used in mass produced bows. Action wood (maple) and action boo are multi layered for stablity and uniformity and are usually cut across the laminations producing something that looks like quarter sawn wood which is more stable than flat sawn wood.

The argument for thin layers makes some sense for bamboo as mentioned above because of the density of "power fibers" falls off from the skin towards the pithy center.

On a related note, anyone know why Mr Bingham specs gluing a reversed lam onto his recurve forms? Why not just cut the form to the shape the lams fill it out to?

[kennym]

"On a related note, anyone know why Mr Bingham specs gluing a reversed lam onto his recurve forms? Why not just cut the form to the shape the lams fill it out to? "

I've wondered that too Shaun. In fact,I just cut the form to shape anymore...

I do have a test bow I built last year with 2 wood lams and 2 glass. 64" -52# @ 28"  Pretty fast too. Don't know how it'll hold up for the long haul,but so far so good.

[insttech1]

Good points all.

I like the part about the lams sliding during the glue-up process; very good point for recurves or serious r/d bows.  Maybe not so much for d-shaped longbows, but then again, those Hills have tons of lams in them.

As far as the wood variances, again good point.  So I guess I would lean toward using fewer lams if using a semi or synthetic material...i.e. actionboo or actionwood, or carbon/foam/glass.

As for the glue lines, yeah they're stronger, but usually heavier than the surrounding wood, so isn't the weight also a performance decreaser?

As for Binghams forms--the lam is supposed to lay over the form, and "cure" any very minor screwups that you had when you cut it out, therefore not making any "strange" contours in your limbs after they are cured.  I did not know that he spec'd it to actually be tapered...

I'm having a string made for a 56" kid's d-shaped longbow that I made form one lam of 1/8" bubinga and .040 glass.  That should be a total thickness of .205", and should give me about 18lbs at 20", or thereabouts.  At least for the kids bows, I have yet to see a lot of reason to throw in any more than two lams...plus the f/g of course.

As far as tri-lams being stronger, well yes, they should be, but I'm talking pure glass bows here, and I would think that the glass would also allow us to use fewer, rather than more, lams to achieve the same goals.

Thanks for the points so far!
Marc

[BAK]

I'm reading a whole lot of armchair theory.  How many of the "experts" have ever shot a Groves bow?  One of the smoothest shooting bows ever made and it had one tapered lamination.  When asked why Mr. Grove was quick to point out that the fewer glue joints he had the less potential he had for failures.

[Dan Bonner]

I have begun to build bows with fewer lams. I use bamboo flooring (actionboo) and have devised a simple, cheap, yet very acurate way to grind paralell lams. I grind core wood for each bow and it is usually over .100 thick and one peice. Have not noted any problems and performance has increased.

I agree that more lams makes a bow easier to get in a form. I dont buy the limb set theory though. Glass or carbon fixes that situation. If you are using natural woods vs. actionwood the homogeneity argument has merrit.

At $20 A pair I know why Bingham specs several sets of lams. I personally prefer less lams and less gluing.

DB

[snapper1d]

I think One Shot and Jason kind of nailed it.I have seen bows with to thick lams in each limb come apart.The thin lams will have more glue lines and will have less chance of a come apart.The ones I have seen come apart split right down the center of the wood lam.On thin lams there is not much room for that to happen.Also I sure do like the thin ones because they sure are easier to fit into the form and glue up.

[SOS]

On my first longbow I used .050 glass back and belly,  and two action wood, one tapered .120 lam and the other the thickest parallel lam - shoots smooth and pretty fast.  I can see multiple lams evening out inconsistencies.  Not necessarily a need for actionwood or action boo.  Other thoughts?

[vermonster13]

BAK I was thinking longbows when he spoke multiple lams. The width of the old Groves Recurve limbs and the thickness of the glass make those a whole different ballpark. Foam cores change a lot of things on new bows also. You don't have to worry about shearing. Heck flatbows had such wide limbs to make up for the qualities of the woods used by many of the native tribes who hunted with such bows.

[sidebuster]

Marc, the only true way to find out is for you to try making one with as little laminations as possible then see what happens as compared to one made with many laminations.