IMO, it's never going to be all math. Take a stick and over bend it, it doesn't matter how precise you are with your calipers. It's and extreme example of process requirements, but I hope you get the idea.
Good point Don, the math/formulas/spreadsheets/programs do have their limitations. They work well up to the point of set taking for wood.
wood is a complex material. it has viscoelastic properties.
https://en.wikipedia.org/wiki/Viscoelasticitythese properties are visible at stresses that typically produce set. When we have just unstrung set that disappears overnight, we are seeing viscoelasticity in action. The wood properties below this point can be predicted well with the programs.
The process requirements you suggest, in order to improve the work of TBB et al, would have to not just categorize wood by species, density and moisture and point of set taking, but also incorporate a method for the bowyer to evaluate the kind of set he is working with, ie. the viscoelasticity of his wood.
For bowyers not looking for the cutting edge of material performance (by not pushing stresses into this viscoelastic zone), woodbears sheet works well by simply specifying a reasonable strain. Woodbears spreadsheet also does a little more, it takes into account set taking, (if you do the bend test), something the other programs do not.
One useful aspect of using programs for design, is stated well by leroy
https://www.primitivearcher.com/smf/index.php/topic,65115.msg987024.html#msg987024I used this program to make a some virtual bows, to see how a specific design works, and understand how it's spreading the stress along the limb. So for me it's an interactive version of the TBB where you can produce F/D curves and experiment with profiles.
It's much easier to make a virtual bow an inch longer or 1/8 inch wider than a physical bow :-;
I haven't used it as a "design" tool, but it's a valuable learning tool.
(as mentioned above, too many variables in real wood compared to laminations)
This mention of woodbears sheet and virtual bow is not to take away from Ryans work. Understanding basic mechanics of materials as lleroy mentions above and Ryans methods show, is what I find so valuable.
The most necessary addition to any "paper" bow needed to make an actual bow is as Mark stated,
You absolutely could do this but it would require measuring each piece of wood for it's individual properties and then making all your calculations based on that.
It does. It isn't too much work to measure MOE of your material, which is by far the most important number to have. I now do a bend test sample for every bow I make to get MOE and go from there.
Mark
