Ok. So I've done one sinew job, and it was on my first attempt at a bow that happened to pop a splinter at a pin knot that I skinned after I recurved the tips. I don't know how good or bad the sinew job was, and I never got the chance to assess what I could do better next time, because it the bow was too far gone and it didn't hold up where that splinter had popped.
I am now working on a 67" osage bow that I have tillered fairly well to 53# at 28"... I say tillered fairly well because I have both limbs bending beautifully and the tips are flipped to the point where the bow is almost a technical recurve, but not quite...problem is, the top limb is a tad stronger than the bottom, and by the time I get the bottom limb slightly stronger like I want it, its going to be in the 49-50# range.
I am making this to be a bow I go after elk with this year, and I want it to come in at 57-59#. So the way I understand it, I have a couple of ways I can go from here.
I can add more recurve, but I really don't think I want to try to increase the severity of the bends at the tips where it's still plenty thick due to the risk of cracking them there. I'm pretty sure that if I come in toward the handle and add more reflex/recurve there...well, I'm afraid it's too thin there for the bends to hold. On top of that, I'm really wanting this to be a slightly reflexed design that is not a true recurve.
Next option is to shorten the limbs, but I'm not sure I want to go that route either...but its an option, albiet one that I'd like to save as a last resort.
Next option is to back it with sinew, and I'm leaning this way. This is going to be my western hunting bow, so I'm not worried about humidity affecting its performance over time. The limbs...I can't remember the exact width of the limbs and I'm out of town until next week...but the limbs are slightly less than 1.5" wide. Its holding a slight bit of reflex from the handle out to about 6" from each tip where the limbs then recurve fairly sharply.
So, here are my sinew questions.
1. Am I correct that I need to add sinew to equal approximately 1/4 the limb thickness to get the true performance increase that can be had with sinew? I've seen where I need to put at least three layers on there to increase performance.
2. Sinew is heaver than wood, so backing all the way to the tips is not as advantageous as ending the sinew backing where the limb tips are stiff and are no longer working. My question here is whether or not I need to tie down/wrap where the sinew ends to keep it from pulling up when its drying? I see where people do this on full length backing jobs to keep the sinew from pulling up off of the recurves, but if the ends of the sinew stop before the recurves, do they need to be wrapped?
3. I've read where folks say you should crown the sinew backing by adding more down the center of the bow than toward the edges of the limbs. Why is this? My understanding, which could be very off, is that if crowned, a smaller, center portion of the width of the back will be the tension plane and thus be doing all or more of the tension work. Sinew can take that extra tension work, but why would you want it to vs having the entire width of the sinew backing doing the work? Is it to keep the sinew back in tension from overpowering the osage belly that is the compression plane...thus possibly lowering the chances that the bow will take a set? Explanations of y'alls understanding on this are greatly appreciated, but simply telling me the best way to do this sinew job will certainly suffice.
Thanks in advance.
