sinew backing and the mass principal?

[echatham]

how do you figure for a sinew backing when following the mass principle?  and while im at it, when using a standard bend test as per the tbb to determine starting dimensions on a new to me wood,  how would using a sinew backing skew your dimensions from what the bend test tells you.  say the bend test tells me i need to be two inches wide, and i know that a sinew backing should let me go narrower.... i feel like maybe 25%  ? but thats just a guess.    btw, thanks Whitefeather for the lovely ERC stave 

[echatham]

ttt

[PEARL DRUMS]

If its ERC your using, keep the width.

[smoke]

I've only backed one bow with sinew so take this for what it is worth: I don't think I'd worry about the mass from sinew.  I know that sinew/glue typically has more mass than wood but I don't think it adds much - I would ignore it with respect to calculating the mass principle. 

[echatham]

Cool.  Thanks guys

[loefflerchuck]

I say don't bother backing osage with sinew unless it's too light, flawed, or very strained with lots of reflex. Junipers on the other hand make magic with sinew. It adds mass but also makes it into a real bow. Sinew juniper is my favorite bow

[mikekeswick]

You would typically add 60 -100 grams of sinew.
The sinew would let you go narrower but I would rather go thinner and keep the width (if i'm in the ballpark and depending on the specific bow). Thinner/wider/sinew means the wood can take more bend,hold more reflex or a combination of the two.
Sinew and glue matrix comes out at around 1.3 s.g. so it is definately worth factoring in!
Juniper and sinew 

[blackhawk]

You can keep the width,make it narrow,and within the mass principle all at the same time.....its called making  it a trapezoid cross section and "crowning" up the sinew along the centerline on the back....and it falls in the "backed" bow rule so subtract 10% for what your intended goal would be for an unbacked self bow....

[Marc St Louis]

I've never sinewed juniper but I would go a bit more narrow and certainly shorter

[echatham]

Thanks guys.  The stave in question is a really clean pipe straight ERC stave with moderate crown.  Theres a half inch of sapwood so i was thinkin id probably reduce it by at least half and decrown it... And then rebuild a little crown with sinew.... But maybe ill leave a little crown in the wood. ill play it by ear.  I have another tree comin down soon that should yield a few more staves.  Think i may try flax on the next one.  Seems to me like that might be a good combo