Bamboo backing

[silent sniper]

My bow building experiences mirror Eric Krewson to a "T". I don't have as many bows under my belt, but I believe Eric is dead-on on every aspect mentioned. .
-Taylor

[willie]

I know bamboo isn't wood but does it's strength correlate, so half as thick would be 8x less stuff.

Good question. I will leave the math up to Mark.  Another aspect of what is casually called "strength" is that bamboo may be able to stretch further than wood on a percentage basis. The percentage a materiel can stretch or compress before rupture (in tension) or set taking (in compression) is actually the technical definition of strain.

[Eric Krewson]

Good grief, you guys are overthinking this stuff.

I try to keep things simple so as not to discourage new bowmakers who think they are incapable of doing the "math".

Fear of failure is the #1 thing that shuts prospective bow makers down, I have seen it over and over when was trying to teach bowmaking to newbies in my shop.

[willie]

I try to keep things simple so as not to discourage new bowmakers who think they are incapable of doing the "math".

I agree Eric. In this thread though,  Allyn, the op is asking.

[PatM]

Conversely though a better grain selected board for a belly might last  a lifetime.

 Bamboo is not like wood through its depth so it's not going to follow the same math as a more homogenous   material

[mmattockx]

I know bamboo isn't wood but does it's strength correlate, so half as thick would be 8x less stuff.

This is correct when it is a solid piece being bent, it is not the case when the bamboo is a thin layer (relative to the stack thickness) forming the back. As a backing it is primarily a tension member, so half the boo will be half as stiff in tension. Note this is only the boo backing, it does not reduce the stack stiffness by half.


Mark

[Eric Krewson]

I have never cut two staves that were the same, even out of the same log so making precise calculations is a moot point.

I have supplied bows to some really serious tournament archers, they shoot every day, lots of arrows. I have found the best made self or bamboo backed bow is going to give up the ghost at somewhere over 200K shots. That would be 2 lifetimes worth of shooting from us normal folk.

[Allyn T]

Eric I will say that fear of failure isn't holding me back. My problem is time constraints, I have a one year old and a wife that thinks I have too many hobbies so I don't have much bow building time. Getting on here and getting as much information as possible is what keeps my interest up and fires my imagination for future bows. I would love to pick someone's brain in person rather than on here but mojam was canceled so I was deprived of that experience. Don't be afraid to get too technical with me, I won't be scared off I promise.

[mmattockx]

I have never cut two staves that were the same, even out of the same log so making precise calculations is a moot point.

I disagree (naturally...  ). You do have to measure the properties of each piece of wood you use and leave a bit of margin to account for the accuracy of the measurements, but it is very possible to do quite accurate design calculations based on measured wood properties and then build to the design dimensions. I think there will always be a bit of final tillering adjustment required due to the nature of wood, but a lot of the guesswork can be eliminated for those of us who haven't built hundreds of bows to get a feel for it.


Mark

[PatM]

How are you measuring the properties?   Few people have access to testing equipment.

[Flntknp17]

......but the math part of this IS why I love it so much.  The science and math behind stress and strain and all of the other physical properties is probably what I love most about making bows.  I don't see why anyone would be scared by it.....math is our friend and it helps us to understand what is going on with bows.  I did my grad school research on strain, so I may be a little slanted, but I still I'm not the only one who likes the technical aspects.  It's what has kept me making bows for so long after I had made all I really needed for hunting.  Certainly natural materials have a lot of inhomogeneity that makes forecasting their behavior challenging, but it's still fun.  I think the anachronism of it is a strong attractor.

Incidentally, bamboo is my favorite backing material   

Matt

[Eric Krewson]

I used the term "math" as a generalization of how to over complicate bowmaking, not actual math.

My hats off to you guys who get into the intricacies of stress of this and that but my point is 99.5% of us cut a stave, make a bow and shoot it, period. We don't even think about the technical side and still make great bows.

My bows have won over a dozen national championships, I guess I did something right.

I understand your position though, I was once a duck decoy carver, I couldn't get enough of duck anatomy, feather detail, art classes and such. I just found it all very interesting much like you guys enjoy the technical side of bow making.

[PatM]

It's the art versus the science.

 Bowmakers are more artist than scientist and they arrive at the correct math through  actually doing.

  People approaching it from the science side  rarely develop the skills to actually execute  what the math tells them, unless they go to CNC cut glass lam bows.

 

[Eric Krewson]

Well said Pat, I am a half fast artist, or was. I have an eye for detail and can see the slightest anomaly in a bows tiller. I can build pretty good flintlock rifle from looking at a picture as well.

One time a great friend and fledgling bow maker sent me a picture of his bow tiller and asked my opinion. I told him he was 1/8" too positive on the top limb. He measured and said "how did you see that, it was exactly 1/8" too positive"? I told him "I just can".

[TimBo]

We don't have to pick one side or another.  Someone who is drawn to wooden bows and primitive archery because of science/engineering/interest in the materials and their properties may learn to appreciate the artistic side.  Someone who is not so interested in these things still can benefit from the growth of community technical knowledge; the Bowyer's Bibles are a good example.  Even though they aren't perfect, they changed the way the "average" self bow looks (and performs) quite a bit.  I definitely agree that actually building bows is the best way to learn, no matter what your initial approach might be!