sinew layers

[jeffp51]

How many layers of sinew can I add at one time, and/or how long do you wait between layers?  Working on a juniper bow--60 inches ntn.

[loefflerchuck]

You can add as many as you want at once. or do one at a time. no need to wait more than a week between layers. Waiting more than that can add issues to the bonding.

[JW_Halverson]

Some claim that curing between courses increases the deflex they produce.  I am not sure about that.  If you live in a high humidity climate, I would recommend curing between courses to prevent the sinew underneath simply rotting before it cures.  Up here where even our rain often tests out as less than 20% humidity, I could lay three layers on and have it cure out just fine. 

[jeffp51]

thanks.  I am thinking 4 layers.  Widest point at the fades is 1.75 inches, and there is a lot of crown on the stave, as the original width was only 2.5-3 inches.  Do you think I should try to build up the edges some, or keep the sinew an even thickness all the way across?

[bradsmith2010]

i usually only wait a day between layers, just because I want to get it done,, I would like to do it all at once but I am just slow,, I think there may be some merit to bonding issues if you wait too long,, but I think if you prepped the last layer, by washing and sizing,, it would work,, cant really advise on how long you could wait and add sinew,, I did it on one bow after a couple of weeks to increase deflex and weight,, the sinew glued on fine,, but the extra weight of the sinew did not add the performance I had hoped for,, I just think my bad on design,, etc,,

[JoJoDapyro]

Jeff, I would try to get the same amount all the way across. Imagine that the tension force is going to go half way through whatever you have in thickness of sinew into the wood. You can violate the grain on the wood in juniper to flatten it out if you want. I split mine, D'ed the belly and decrowned the back. Then added sinew.

[JW_Halverson]

If your first course is well lapped bundle over bundle, with no gaps or such, a second heavy course down the center of the bow will boost your draw length nicely.  Additional courses beyond that have less and less effect because they are heavier than wood. By not going all the way across the width of the limb, that last layer is lighter, but still shifts the plane of neutrality such that it does as much as as whole course. 

[JonW]

Guys don't you mean REFLEX not deflex?

[jeffp51]

Joe, is that the back or the belly you are showing there?  pretty grain.  I am also leaving the belly D shaped for now.  Not only does TBB IV suggest that is the way to go with sapling bows, but it also just feels right.

[JoJoDapyro]

That is the back.

[simson]

If your first course is well lapped bundle over bundle, with no gaps or such, a second heavy course down the center of the bow will boost your draw length nicely.  Additional courses beyond that have less and less effect because they are heavier than wood. By not going all the way across the width of the limb, that last layer is lighter, but still shifts the plane of neutrality such that it does as much as as whole course.

Good advice!
When I sinew a bow I always try to get a crowned back (saves a lot of mass) and when you have a crowned stave - the better!

[JW_Halverson]

Guys don't you mean REFLEX not deflex?

Uh, derrrrrrr.....

Sign me,
Omma Jean-yus

[jeffp51]

I put down two full layers, and a third course down the middle.  Then I wrapped and heated it.  I was surprised this morning at how thin it all became--I thought I was putting on tons. I can add another layer, but how do you know when you have enough?  Also,  do you have to pull it into reflex before it dries, or will it reflex as it cures?

In the pictures below, the reflex clamping was done this morning after a night of drying.  I don't really know if it will make a difference at this point, or if or how long I should leave it like this, or if I should add more sinew.  What have others experienced?  This is my first time.  Be gentle.

[PatM]

You should reverse brace before you sinew and then use the stick through the string to crank in more reflex as it dries.  Get rid of that clamp.  Also to get your sinew lying straighter next time..

[JW_Halverson]

Resist the urge to add more and more sinew!  You have plenty on it now.  The sinew is resistant to stretch and a little is enough to stop the wood underneath from stretching under tension.  At this point, you have almost no stretch to the back of the bow, adding more will only add mass to your limbs, you are at the point of diminishing returns.