Dry vs "seasoned" sinew

[Pat B]

The Massey Medicine Bow I built a while back had the most drastic changes of any other sinew backed bow I've built, which isn't many. That bow is sinew backed hickory with a rawhide covering. The draw weight of that bow has gone from 55# to 45# and up to 65# all depending on the R/H. The tiller didn't change and the bow still shoots OK but when the humidity is high this bow becomes a noodle.

[RidgeRunner]

I think there are things about Sinew Backed Bows that we are just now starting to learn.
Pat B's last post.....  Some wood/sinew combonations may not work as well as others.
Hickory absorbs moisture far faster than Osage.  Could it be that this new moisture soaks right into the sinew far faster and effects the tiller.  Something to think about.

Something else.  Eric sort of hit on this.  Many of the strongest glues form molecular bonds with the materials they are supposed to hold torether and within the glue itself.  Cant say that I know how long it takes for most of those bonds to be made.  Cant say that I know if the bond making stops when the moisture is gone....  Could be that it continues for quite some time.

David

[Pat B]

David, when I built this bow I was copying the last bow Jay Massey built before he died from a hickory tree at his dead brother's house. Jay also had a rawhide covering over the sinew. All the components, hickory, sinew, hid glue and rawhide are hygroscopic meaning they take on and release moisture to the atmosphere as the R/H changes. Knowing this, I gave this bow a good coat of Massey finish, 3 or 4 coats of Tru-Oil and spray satin poly thinking it would at least slow the hygroscopic rate but I learned a good lesson about R/H and it's effects on wood bows.

[Eric Garza]

Screw sinew anyways,its overrated 

I snickered when I saw this, but I have no choice but to agree with you for most bows, especially for modern wood bows that tend to be over 60 inches in length. Sinew works magic when laid on woods that are compression strong and not too dense, like yew, juniper and eastern red cedar (which is actually a juniper, not sure why we keep calling it a cedar). It seems to add modest benefits to heat treated elm, white ash and eastern hophornbeam, and marginal benefits to osage when you can actually get it to stick. Other woods... meh.

I'm also amazed at how long of bows people will try to sinew back. Anything over 55 inches just doesn't seem worth it to me. Sinew adds too much weight per unit strength, even when you absolutely minimize the amount of glue in the backing. I'll sinew back short bows, but anything over 55 inches either gets a rawhide backing or some sort of fabric. I just had a gentleman ask about buying several ounces of sinew to back a bunch of 60+ inch hickory bows. I talked him out if it. The time spent sinew backing those bows just wouldn't have yielded a good return on investment, in my opinion.

[PatM]

Sometimes the "weight gain" of a bow over 20 years is a loss of strength of the owner
 I think Marc  may be talking about going out of tiller rather than an increase in draw weight.

By definition they are the same thing?

The tiller definition? No. Marc refers to tiller changing and PatB refers to "tillering" the bow to a reduced weight due to the bow gaining weight.

[PEARL DRUMS]

55" cant cover all draw lengths. The person pulling 29 or 30" may full well benefit from sinewing a 60-62" bow.

[Josh B]

I've only had it drastically change on me once.  I would of sworn the sinew was dry after five weeks.  I tillered it to 60# and finished it out.  I shipped it out and it sat a couple of weeks before the new owner shot it.  It had gained ten pounds.  I suspect there was still some moisture in the wood from sinewing it, but that's just a guess.  Whatever happened, it was a bit embarrassing.  I give sinew an extra month of drying time before tillering now.  Josh

[Marc St Louis]

I don't wait more than 2 months with wood bows.  I suspect that the long wait has more to do with horn bows.  Once you have the horn glued down onto the wood core it acts quite a bit like a moisture barrier so when the sinew is applied all the moisture from that gets absorbed by the wood and as the sinew dries it also locks moisture inside, double whammy.

[Eric Garza]

55" cant cover all draw lengths. The person pulling 29 or 30" may full well benefit from sinewing a 60-62" bow.

The person drawing 29 or 30 inches might benefit from having their bow backed, but I'm not sure they'd benefit from having their bow backed with sinew. I'd probably go with rawhide or fabric instead. But that's just me, and I don't pretend to be infallible.

[PatM]

Rawhide and fabric don't have an potential to  DO any work though. Sinew is magic on a bow when you use it to go beyond the 2:1 bow to draw ratio. Particularly when there is only sinew on the actual bending portions.

[Eric Garza]

Rawhide and fabric don't have an potential to  DO any work though. Sinew is magic on a bow when you use it to go beyond the 2:1 bow to draw ratio. Particularly when there is only sinew on the actual bending portions.

This sounds very peculiar to me. Are you claiming that rawhide and fabric, which both add mass to a bow, don't offer any resistance to bending when applied to a bow's back and therefore shoulder none of the 'work' of the bending portion of the limbs?

[PEARL DRUMS]

Cant answer for PatM, but my answer is no. Rawhide nor fabric add any noticeable bend resistance. Protection from splinters? Heck yes!

[PatM]

Like PD says. Try measuring the draw weight of a bow and then adding rawhide or cloth and compare again.

[Josh B]

Eric I think you might have missed the point that Pearly was making.  When it comes to bows, short is a relative term.   For a 26" draw, 60" is not short, but for 30" draw 60" is relatively short.  The idea of sinew's weight being a disadvantage on longer bows is based on the premise that it's not being worked hard enough to achieve efficiency.   Relatively speaking, sinew would be earning its keep on a 70" bow IF the draw length was 35" or better.  Conversely, sinew would not be optimal on a 50" bow IF the draw was only 20".   I hope that makes sense.  Josh

[Carson (CMB)]

I tend to think that seasoned sinew backed bows are less affected by Relative humidity changes than a newly finished sinew-backed bow.  Seasoning = stabilizing.  I dont just mean stable in terms of the tiller walking around on you as it continues to dry, but that it is less likely to react dramatically to exposure to higher RH.  Just a hunch. 

Keep in mind there were waterproofing additives often used with hide glue that might have extended the drying time.