Pros and cons to different stacks

[Troy D. Breeding]

Just wondering if anyone has ever tried using different type stacks when building a bow.

Simply put, most recurves only have one parallel, one taper and the two pieces of glass in the limbs.

Lately, I've been using two veneers and one taper.

In the bow I'm currently working on I had to add in another very thin parallel to bring the stack thickness to the correct measurement.

I know back several years ago I got a wild hair and made a R/D longbow that had 9 lams in the limbs not counting the glass. If I remember right the thickest lams were the two .050" tapers in .001" taper.

This bow seemed to be the smoothest of all the longbows I made.

Now I'm thinking about trying a recurve with several thin lams to see what will happen. Since I normally use one .003" taper I could easily switch that to three thin .001" tapers and three very thin parallels/veneers to make one a six layer count.

Lets hear your thoughts...

Troy

[beachbowhunter]

I think some guys are doing that using carbon, with a couple lams on the back side where it is useful (they skip the glass of course). Personally, I think thinner lams lay down and clamp better for curing. I suppose there is only one way to find out.....go for it!

[Swissbow]

Hey Troy, what was the profile of your bow ( moderate or pronounced deflex/reflex ) and what was your total taper ?

Some people say that the energy is stored in the gluelines between the lams. Therefore more lams would store more energy. On the other hand i believe that the glue doesn't add to the performance and the less you have in the bow the better. To find the best compromise between the two one would have to build the same bow with different number of lams and compare them.

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Andy

[Troy D. Breeding]

Andy,

That was exactly what I did with the (moderate) R/D longbow. I had built one with a total of .100" in one .002" taper, three .060" parallels and two pieces of .040 glass for a total of .360"

Then I built one with two .050" tapers in .001", one .030" parallel, six .025" parallels and two pieces of .040" glass for a total of .360".

Both bows finished out at 60#@ 28".

I had several different people shoot both bows and only one fellow said the 5 lam stack shot better. I think he was looking more at the color combo than how it shot. Guess I should have made both bows with black glass and as close to the same look as possible.

Never chronoed the bows together. I was just comparing how they felt in draw and when the arrow was turned loose. The 9 lam had no hand shock (to me) while the 5 lam had a very slight thump.

I know there are several things that could have also helped the design. Like more taper in the limbs for one, and different string material for another. Both were shot with dacron strings.

Troy

[bigbob2]

Havent been building laminated bows that long but all mine consist of at least 4 lams, all tapers and no parallels. Turn out very smooth to draw and the force/draw curve shows no 'stack' at all on the draw.Happy with things.

[Crooked Stic]

What is happening here guys is with the more lams they are moving on glue up and comforming to your form and when cured and out of the form they have less spring back. So that will give the power stroke a bit more travel.And I suppose they could be a bit smoother. Although if you had a layup that pulled like a 2x4 and expected several lams to fix it I think you would be dissapointed.

[Troy D. Breeding]

Mike,

The idea for trying it came to mind after using and LVL beam for a pick board while working on the second story of a house. After we were through the beam was still straight where in the past we had used 2x10's and they would be warped.

My thought was, that if that beam could handle heavy folks walking across it all day and still be straight it had to retain good recovery factors.

Good recovery should make for a better bow limb.

Guess I'll just have to try it again and see what happens.

Troy

[Trux Turning]

Troy-I have to agree with Mike on the multiple lams-there has to also be a point of diminishing returns on the number you put into a bow. 2 lams are better than 1 but will 9 be better than 4 or 5?? The other thing to factor in are the characteristics of the lams themselves- multiple lams may enhance the characteristics of some woods and have liitle effect on others.

[flyfish1]

Too many glue lines would add more weight. In Byron Fergusons book he tested the multiple lam thing and said @ 5 lams the extra one was not worth the time/expense in performance if I recall. He knows a little about it.

[Troy D. Breeding]

FF1,

The bow I did with 9 lams had the same stack thickness as the other with no increase in weight.

Troy

[bigbob2]

Because I use tapers on all lams for my longbows, and I made a 75# @ 28'' recently I used 5 lams as using just 4 lams, each lam would have been over .0120, making them a bit bulky in my humble opinion.Seemed to draw very well at least as far as this old goat can still draw.

[flyfish1]

Are you talking draw weight? The epoxy adds mass to the limb therefore making limb slower .

[Troy D. Breeding]

Ron,

The draw weight was the same. Wouldn't think the glue would add enough mass weight to see any noticable difference. Have you ever taken the drop part of a limb an really looked at how thin a glue line is.

Troy

[rmorris]

I decide how many lamination I need by trying to keep all lamination under .080. I look at it like this...  the thicker a single lamination in my case bamboo is , the more internal shear force it has. If  you were to take a piece of bamboo that is .020 thick and a piece that is .120 thick and bend them till they break, the thick one breaks much sooner. If I were to need a stack of .260 using .050 glass I would have 2 lamination one parallel at .080 and one .002 taper that measures .080 at the fadeout( rough thickness would be .100 at the butt and .040 at the tips). If I needed a stack of .300 with the same glass I would use 1 .002 taper that is .070 at the fadeout and 2 parallels that are .065. When you start adding in veneers this changes things just a little but I think you get the idea.

[rmorris]

Next time I glue up a limb I will do an experiment to see how much 1 glue line adds to the physical weight of that limb. Isn't science cool?

[kennym]

Originally posted by rmorris:
Next time I glue up a limb I will do an experiment to see how much 1 glue line adds to the physical weight of that limb. Isn't science cool?

That will be some good info right there!!  

[BenBow]

I'd recommend you weigh the lams first than compare weights after glue up using the percentage difference to get an apples to apples comparison. Otherwise the wood density differences may be enough to negate any true differences.

[Tron]

I'm thinking about 4 .001 tapers and two veneers in my next one (heavy R/D longbow).  Also on a new form with more reflex at the tip.  We'll see how it goes.  At the very least it will look cool

[Crooked Stic]

Dont think glue mass is gonna be a factor to worry about.
What amazes me anyway is is the job smooth-on does holding all the pieces together for thousands of shots.