Sinew backed prod - hide glue cracking under stress? UPDATE: Bow is braced (pic)

[tkdHayk]

Bow Length: 40 inches
Wood: Red oak
Backing: 3 layers of Sinew/Hide Glue (1.5mm thick). Each layer of sinew had 1-2 weeks of drying time.


crossbow stock:


Required Draw length: 15.5 inches
Desired draw weight: at least 65# at 15.5 inches

As I floor tiller the bow, I hear cracking , and then notice that the hide glue has cracks in it which are perpendicular to the length of the bow.
http://imgur.com/Nh91Wk7

Should I be worried? I poured excess glue on to the bow after applying each layer of sinew. the glue was relative tick. I could re heat and smear/flatter the hide glue to remove the cracks. or I could just ignore it and proceed with bracing the bow, since the sinew itself seems unaffected and is unlikely to fail. What do you think?


UPDATE: I added an extra layer of sinew, using less hide glue than I did on
the other layers. The bow has been brace: http://imgur.com/nNaOqmr

[Pat B]

It is probably just the glue. Too much glue can do that. Generally the only harm it causes is an uneasy feeling when heard. It does add excess physical weight which can inhibit the bow's action.

[tkdHayk]

It is probably just the glue. Too much glue can do that. Generally the only harm it causes is an uneasy feeling when heard. It does add excess physical weight which can inhibit the bow's action.

I hope so! the excess glue will probably shrink some as is dehydrates further. PS, can you see all 3 of my images? not sure why only 1 of them got uploaded.

[loon]

could it be that the glue was heated too much?
The hornbowyer Beaumont Vance in the Facebook hornbowyers, atarn groups has written about how he avoids precisely this cracking problem. Basically, he first sizes the wood many times with thin fish bladder glue, then uses very thick hide glue with the sinew...

[tkdHayk]

could it be that the glue was heated too much?
The hornbowyer Beaumont Vance in the Facebook hornbowyers, atarn groups has written about how he avoids precisely this cracking problem. Basically, he first sizes the wood many times with thin fish bladder glue, then uses very thick hide glue with the sinew...

I did size my bow with Hide glue (not fish glue). I wonder what difference it makes. When the cracks happened, I was floor tillering in the sun, so it may be that the glue started to get weak due to the heat. How does hide glue generally hold up to dry heat?

[PatM]

Too much glue and perhaps poor quality glue.

[Pat B]

You said you poured the extra glue over the sinew. That right there is too much glue.
 When I add sinew I first wash the bow with Dawn soap and rinse with boiling water. I also wash the sinew with Dawn and rinse with warm water. This cleans the back well and preps the wood to help the hide glue adhere. I them size the bow with a couple of thin brushings of hide glue then begin adding the sinew. I like moistened sinew before going in the warm hide glue, squeegee off the excess glue with my fingers and lay it down. That is all the glue I use, just enough to saturate the sinew then squeeze most out and lay it down.
 

[mikekeswick]

It is not too much glue - it is too concentrated glue.
It has to be over 40% solution to start making the cracking noises. Next time just be more careful about how much glue to water you use. 30 - 35% is as concentrated as you ever need to go. Nothing to do with sizing or the extra glue you poured over. Unfortunately it will continue to make these noises when you haven't used it for a while. Nothing you can do about it now other than soak the sinew off and try again - or live with it

[Del the cat]

Maybe picture files too big?
Del

[JW_Halverson]

I remember the first few sinew backed bows cracking across the back like this.  I was eager to get the sinew on and rushed through processing the fibers as well as laying on the bundles.  I ended up with gnarly, ropey, nasty sinew.  There were fissures and low spots that I thought I would fill with hide glue.  So, I used the stuff like plaster to fill everything in. 

BAD mistake. Any job it did was merely cosmetic, a bad sinew job is a bad sinew job. The excess glue does not have the strength of the sinew and it will crack.  My lessons learned: 1) process the sinew into thread like fibers 2) smaller bundles, well hydrated, and combed straight so all fibers are parallel.  3) work the glue into the fiber bundles,and then gently squeeze it out - I needed far less glue than I thought.

[bradsmith2010]

I have had the glue make cracks ,, even when I thought I was very careful,, the bow didnt make noise,, and held up fine, but I could see some sideways cracks in the glue,, I think alot of times we cover or paint the sinew,, so it is not noticeable,,

[BowEd]

As long as the sinew does'nt lift or tear or something like that.That's a bond issue then.Don't see that happening here.The way it is now you'll just have to put up with it but feel as though it is safe yet.

[PatM]

I've never found  glue/water ratio made any difference to cracking or not. It all dries to about  90% or so glue.  What a higher initial ratio will give you is potentially more total glue left over which is where people run into cracking problems as many have noted.

 Thick glue well squeezed out to the optimum glue/sinew ratio doesn't make cracking noises.

[hoosierf]

I've had a few sinew backed bows do that. After the hide glue is fully cured. Sand it with 180 grit and then "size" or seal it with a layer of Elmers Maxx or Titebond. The Maxx which I prefer often gives it a reddish hue when I've done this and it's kinda cool. The cracks become almost completely invisible. It's a reasonable way to save the appearance. I doubt the performance is impacted at this point.

[tkdHayk]

Greetings bowyers,

Interesting and somewhat contradictory responses guys, thank you. To clarify a couple of things:

-I am not concerned with the bow's appearance. The cracks are very small and the bow is very beautiful and smells amazing.

-I don't know if you guys got the up close photo of the cracks, here it is: http://imgur.com/Nh91Wk7

-Perhaps I have indeed used "too much" hide glue, or too high of a Glue/Water ratio. But my question is A) should I be worried about the tensile capability of my backing? Could a sudden crack in hide glue travel down and crack the sinew? Sort of like how an object is easier to shatter when it is surrounded by ice. Is that the case at all? Because If the cracks don't cause the backing to fail, I'll keep pouring extra glue for maximum adhesion. I don't mind cracks if they do not undermine the structural integrity of the bow. what be your thoughts?

Hayk