BB IV and mass theory?

[D. Tiller]

I dont get it! I understand it has something to do with the Standard Density of the wood but I dont get how that helps you design the bow. Help!!!! Does it mean the if the SD is lower just build it wider or longer?  Whats the base line?

So confused!

[Rich Saffold]

It's also called specific gravity or sg. It's really the amount of wood in the wood. At 1.0sg is where wood starts to sink. Kinda like humans are at 1.0 . Let the air out and down ya go..

In general if you had two identical pieces of wood except one had a density of 1.0 and the other was .5. You would make the .5 sg bow twice as wide or wider and longer to equal the mass of the 1.0 sg bow.

Naturally woods have their own strengths and weaknesses, like being tension or compression strong, or balanced  so this plays into the design equation as well.

[Badger]

Tiller, the basic base line is that you are trading measuring width in the bow for measuring mass weight of the bow. Every style of bow, every draw weight of bows and every different wood you use to make a bow will change the ideal demensions of the bow, far to many to list anywhere. This just gives you a formula to figure out how much a certain style of bow should weigh and ignores the wood you are using to build it. You will find certain woods can be made a bit lighter but it will keep you pretty close to good demensions when finished. I also find that bamboo backed bows can run about 10% lighter than the formula suggests. Heat treating bows will also allow for less mass weight. I am curious to see how the public understands it.

[DanaM]

I find it useful, still trying to wrap my brain around it. But the more I use it
the more value it has. I'm learning to start wide and reduce the mass by side tillering.
The maple bow I just posted came in light and took a bit of set if I woul have left it a bit
wider I would have been right on target for the prjected mass. The bow shoots hard and is
showing no signs of belly failure but it is a little underbuilt.

[JackCrafty]

Mass theory is "big picture" stuff.  It's strategic rather than tactical.  For example, a tactical tool is the chronograph.  Mass theory will help "guide" your bow building toward the best results....not measure it like the chronograph.  The baseline is the chart provided in TTB4.
It's an awesome tool (IMHO).

[D. Tiller]

I'll read through the chapter again. Tech stuff drives me a bit batty! Thanks guys!

David T