Starting limb thickness?

[cool_98_555]

Hello everyone,

I am wondering what the minimum starting limb thickness would be for various desired draw weights with osage.  For example, if I wanted a 90# bow, would 5/8" thick be the minimum to start with at the limbs to safely achieve that draw weight, or would you need more wood in the limbs to start with to achieve that particular draw weight?  I have made warbows before that have started out just over 1" thick parallel for the entire limb and I was able to achieve over 100#.  Looking for 90# on this one and wondering if 5/8" is enough thickness to start with.

Thank you!

[Badger]

    Thickness is determined by how much bending limb you have to work with. Draw weight should be controlled by width. In theory there is only one correct thickness for any given style of bow regardless of draw weight. Of course we don't stick to that theory exactly but it is good to keep in mind. If you are building a 66" long 28" draw stiff handled osage long bow you might be about 1/2 thick and 1 3/4 wide. If you are doing a 72" english long bow you might be 3/4" thick. It just depends on the style.

[stuckinthemud]

     Draw weight should be controlled by width.

So that is why I really have been struggling to get draw weight down - I've been doing it on thickness - thanks Badger, that's gonna make a huge difference to my bow-building - so get the bow tillered right then tweek the weight by reducing width?

[Pat B]

If I'm starting with a tree stave I go to about 3/4" at the fades then reduce to floor tiller.

[bushboy]

I agree with Pat b.the Bend resistance can vary from tree to tree and even within the same log.I don't build heavy draw weight bows but I suspect the same rules apply depending on the density of the stave.

[Knoll]

Badger . . . in your use of the term "style" are you incorporating both the style (elb, bendy handle, d/r, etc.) AND its length?

[FilipT]

By width? First time I hear that.

[High-Desert]

Badger- could you elaborate on that? I'm curious what you mean. Or did I take your statement way too literal? I've always taken width and thickness as two dependent variables that are affected by length and draw weight etc.

Just my thoughts here. Assuming the other variables the same, i.e. Length, wood type etc. If thickness was constant, and you varied just the width to gain draw weight, then doubling your width, doubles draw length, which would double mass, which would be way over built. Wouldn't it?

Eric

[Badger]

      I have never figured out a way to really know exactly what a thickness should be before starting a bow. Just relying on experience I know that 1 1/4 "  wide piece of osage will usually give me a 64" stiff handled bow that will draw 28" @ 50#. So this is a starting point.

     If you take it a step further you can use the no set tillering method to hone in on the best match of width and thickness. Being a little overbuilt is never a problem, being underbuilt can be a problem. Every slight change in design will have an affect on the best thickness for a bow. Longer draw lengths, more reflex, less working limbs etc. all require a limb to bend more so will need a thinner limb, this usually also means a bit wider. The lowest mass bow will always be a bend through the handle bow with a circular tiller, it will also be the narrowest and the thickest.

    As you can see here it is obvious I can't answer the question because there is too many variables. This is exactly why I came up with the mass theory. It adds mass for everything that asks a limb to bend more. The mass is usually reflected in width. The correct thickness will then find itself as you tiller.

  The one statement I made about only one correct thickness for a given design, I should have said best thickness for a given design. There is a fairly wide range that will work well with some woods and a narrower range with other woods.

[Badger]

      A good thing to remember, thickness determines how tight of a radius something can bend, width determines how far it will bend.