Questions for the Wood Gurus

[D.A. Davis]

I've got a couple questions for the wood gurus on the Board.  From what I've read, when choosing a particular wood for use in a riser, it's always a good to use the Specific Gravity to determine a woods hardness/strength.  I read where you should only use woods with a Specific Gravity of over .50 in a riser without other means of support.  

My question is, can you get too much of a good thing?  I mean, can you choose a wood with too high of a Specific Gravity?

Next, when considering lamination's, what makes a good wood for use in lamination's?  I know there are several time proven woods, and man-made products, that make fine bow lamination's.  But, what tells you that a wood should never be considered for use in the bow limbs as the parallels and tapers?

[KenH]

Personally I choose woods, in part based on their Janka Hardness rating, not Specific Gravity; and in part on the beauty of the wood.

If you're building classic wood-fiberglass composite bows, the kind of wood between the two pieces of glass almost does not matter, as the glass provides 88% of the strength of the bow.  What the wood does, structurally, is separate the two pieces of glass and the distance between the two glass strips defines the draw weight of the bow, more or less.  

I wouldn't use Balsa or Aspen, but have used nice straight grain Fir/Pine to make very good shooting bows.

[D.A. Davis]

Okay KenH.  I've learned something tonight.  What is the desired number range on the Janka Hardness Scale?

[mikkekeswick]

For a core wood you want great gluing properties and not too high density (upto say 0.70 s.g. or else you have got limbs that weigh more than they) need to and so won't return as fast. Suitable core woods are black walnut, hard maple, birch, bamboo flooring, ash etc.
You are on the right track with the riser wood. If you want to know if a wood is hard or not then simply try to dig your thumb nail into it. Doing this over time will let you build up a feel for it. After all the average numbers are fine but there can be such a large difference between wood from the same species that you need to learn how to judge them for yourself.

[LittleBen]

All great advice so far.

I'd just add that I don't think you can go *too* heavy for the riser wood unless you wanna keep the bow very light (mass). This is more of a personal thing than limb cores I think.

.50SG or greater seems like a good general guideline. In practice that would mean something like: walnut would be ok, but probably not poplar without some other support like penolic or hardwood I-beam of some kind. And under that rule you could go heavier obviously like an Ipe riser if you wanted.

[BigJim]

Too heavy or dense/ hard wont hurt for a riser in a laminated bow. If you don't have a good working knowledge of hardwoods and don't  want to do your own testing, I would try to stay with known and readily used riser woods.

More bows fail due to poor assembly and design than do of improper materials...but that's probably because most use know "good" materials.

Although many limb cores will be suitable, It is best to choose them because of their overall weight and elasticity. Not too likely that by using a out of the norm wood that you will see any gains or save much of any money.
In general, the cost of core wood is pretty low. It's the effort of turning it in to lams that adds the expense.
With most solid woods you will experience waste, but with actionboo, the entire board is useable...shy a small drop.

bigjim