Specific Gravity Question

[wvarcher]

     Do anybody take into consideration the Specific G. of a wood before you make a bow out of it?  I have made bows from trees with similar SG like Sassafras and Red Elm, and i usually have to make the Sassafras bow much wider to keep the set about the same as an Elm bow.  Why does the Sassafras need to have wider limbs?

[Justin Snyder]

Density is only one portion of wood evaluation.  You need to have an idea of compression and tension strength of the wood.  Woods that are weak in compression can take more set if built too narrow. I like building backed bows from woods that are super strong in compression and have a high SG with backings that are super strong in tension.  You get the best of both worlds. Justin

[DanaM]

Badgers mass theory is a good way to go, it inherently takes into account the density of the wood.

With an untried wood I will start wide then utilizing the mass and monitoring set while tillering I will narrow the width as I tiller.

[son of massey]

  SG is a good starting point, it at least tells you about how "solid" the wood will be.   as far as using it alone to directly design your bow, you will find it will be inadequate.   iron has a high SG, but it would not be a good candidate for a self bow as the energy storage that it can do before it has material deformation is not high-it would take permanent set easily.   it is a good indicator but not a good ruler. SOM

[JackCrafty]

I used to pay a lot of attention to wood with high SG, but I've switched to wood with high MOE (modulus of elasticity).  I now prefer to work with wood with relatively low SG combined with high MOE.  This type of wood is a good fit for the sinew-backed bows that I like to build.

[DanaM]

I used to pay a lot of attention to wood with high SG, but I've switched to wood with high MOE (modulus of elasticity).  I now prefer to work with wood with relatively low SG combined with high MOE.  This type of wood is a good fit for the sinew-backed bows that I like to build.

Patrick what woods specifically are ya talking about? I' haven't done a sinew backed bow but its on the menu.

[adb]

I used to pay a lot of attention to wood with high SG, but I've switched to wood with high MOE (modulus of elasticity).  I now prefer to work with wood with relatively low SG combined with high MOE.  This type of wood is a good fit for the sinew-backed bows that I like to build.

yew.

[wvarcher]

Thanks everyone for all the informative responses.  I guess two different pieces of wood with a similar SG won't always have the same strength in tension and compression.

[JackCrafty]

Dana, elm and juniper. White ash, birch, black walnut and some of the red oaks fall into this category as well.  I've tried ash and don't like it much (for short bows)....I really need to get some birch staves so I can experiment with it, I've never worked with black walnut (and probably won't), and I'm going to try my hand at making a sinew backed red oak bow for my next build-along.

adb, yeah, I need to get my hands on some yew.....



PS. After a little more research, sweetgum could probably be added to the list and the red oaks look a little heavy....but might still work.  Can't seem to get good data on mulberry....