how many lams?

[JamesV]

All things being equal, how does the number of lams effect overal performance. If I build two identical bows, one with a single action bamboo lam with glass on both sides, that would be two glue lines and another with 4 lams that would be 5 glue lines, would there be any significant difference in performance?

James..................

[Dick in Seattle]

Incomplete question...   what is the weight of the bow?   All things being equal, and they never are, more glue lines are a detriment to performance.   However, the thicker the lams in relation to the draw weight, the stiffer the draw will be.  

The action in the lam is a combination of stretching and compression... stretching on the back, compression on the belly.   The thicker the lam, the more stretching and compression has to be accomplished.   Think of a column of marching men, making a turn.  The men on the outside have to march faster, the men on the inside have to take smaller steps and bunch up.   The wider the column, the more disparity there is in the movement of the men on the outside vs. the inside.

In a bow, if it is one lam, only two surfaces are available to distribute the stretching and compression.  Make it two lams and you have four surfaces... half as much stretching and compression per each.   Three lams... well, you get the picture.

I built a series of bows from four lams to one, as you suggest, and played with it.  At light weights (most of my builds, since I'm a sensible old man), two lams is fine, three maybe a bit smoother over 35#.   45# to 60# four is good.  Over that, you may begin to feel some additional smoothness from five lams.    

I think the effect of distributing the stretching and compression over a few lams is greater than the performance loss from the glue lines, but there's a point where it gets, well.. pointless.   As I said, up to about 40# two or three lams is plenty and will give you a nice smooth bow.   Putting more lams than that into a light bow means working with very thin lams and more glue and just isn't worth it.  In a heavier bow, there is more to gain from the extra lams and more substance to work with in terms of grinding them and handling the build.

Just for the record, my one lam (essentially a glassed self bow) cherry bow is 30#.  I can feel that it is a bit stiffer than my other bows of similar weight, but it's still not at all unpleasant to shoot and is a good performer.

Hope that helps a bit.

[Carpdaddy]

Wow Dick, great explanation, very helpful post.
Thanks

[jsweka]

...my one lam (essentially a glassed self bow) cherry bow is 30#. I can feel that it is a bit stiffer than my other bows of similar weight

Dick - I haven't experimented with different lam numbers like you have, so I don't have any experience in this department, but I'm having a hard time wrapping my mind around your statement above.  How can a bow with only one lam be stiffer, but still be at similar draw weight?  Do you mean that it stacks faster than a multi-lam bow?    

John

[Dick in Seattle]

John... I guess so.. just seems a little bit more of a pull  getting to anchor, though the end result is the same.   I think the compression just builds up faster.

Draw weight doesn't tell you as much about how a bow draws or performs as we like to think it does.  There are too many variables in the design, construction and wood.  I've had a number of Hill bows built to exactly the same weight, and they'd feel just slightly different.  I've also had identical specific model Hill bows that had as much difference in feel between them as between two alike Hills but of different models.  Not talking extremes here, just noticeable. Most everyone who has experience with a number of Hills seems to feel that the yew models are a bit smoother than the bamboos, though not as fast.  Glass is the biggest factor in the bow, but the wood is there, too.  I know perfectly well that I'm often sacrificing some speed when I put pretty, but heavy, woods in a bow and try to make up for it by using boo in between.  I wouldn't build if I couldn't play with pretty woods, though.  

Sometimes I think trees take on attitude as they grow!   I look for boards from nice friendly trees...  :^)

Seriously, if you ever want to really experience how much difference there can be, try pulling an old Bear recurve and a new copy of same, same weight.   The old bows were built with less pre-stress, more concern for smoothness.  The new ones pack on more weight early in the draw to get the speed everyone demands now.  You end up pulling that extra weight through the length of the draw, even though you end up at the same result.  I haven't done enough playing to be sure, but I kind of suspect this  might be more true of recurves, and maybe some RD's, than of old style straight longbows.  These seem to me to chart more even power lines.

Example:  Back when I could still draw 45#, I had a very smooth, easy drawing Super Kodiak 45#.   I was already losing some strength but I could shoot that bow through a 40 target course.  However, it was an old bow and Predator came out with that gorgeous reproduction of it.  I gave in and bought one, 45#.  When it came I strung it up and discovered I absolutely could not get it to full draw.  My arm started quivering from pulling the pre-load through the first half of the draw.  Great bow, and a beauty, but I couldn't shoot it.  Rested a bit and went back to my old one and it was fine.   I'm sure the new one was a faster bow, but it wasn't for me.

What I like about bows... they're endlessly fascinating to think about... Not saying I always think right, but they always make me think.

[JamesV]

Dick...........

Thanks for you thoughts, very interesting

James..................

[jsweka]

Thanks Dick.  That makes more sense to me now.

John

[ChristopherO]

And he is talking about longbows!  Think what this discussion would be like when recurves are factored in....

[Dick in Seattle]

Christopher....   Yep... good reason I don't build recurves!  There's a whole nother set of factors...  how much curve, where it occurs in the limbs, amount of width and taper to the limbs, undoubtedly more that I'm not even aware of.  I have great admiration for the guys who play that very detailed and intricate game.   RD's are the same... how much R, how much D, etc.   I'm just beginning to explore extreme string follow on longbows, having built three, and reflex, having built one.  I'm fortunate that the straight longbows are what appeals to me, though I do actually shoot recurves better.  As my wife says, I do everything the hard way!  Go figure...

[NYArrow]

Thanks for the lesson Dick. Perfect example of how experience trumps knowledge gained from a book.

[Swissbow]

I agree with Dick about the distribution of the stress if you have more lams and I also think that with three or four lams you get better performance than just with one all other things as equal as possible. This is due to the fact that a multi lam bow stores the energy not only at the surface but also at the glue lines. Just think of the perry reflex design.

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Andy