Horizontal cracks on a sinew backing?

[ajbruggink]

Hey guys,

I have a question about something that started happening to a bow I was working. I started sinew-backing a red oak stave that I missed the target weight big time on and I was trying to get the draw weight back up a bit. I put on one course and then I didn't get back to it and after it had dried I decided to string the bow and see how it shot with a single layer of sinew on it. For a couple of practice sessions the bow shot fine but then I began to hear some weird sounds as I would pull the bow back and after examining the bow, I found some cracking was occurring on the bow's back, which I am providing pictures of. What is going on and what is causing it? Your replies are greatly appreciated.

Thank you,

Aaron
https://imgur.com/XkjFdk4
https://imgur.com/RQNAJ2M
https://imgur.com/HW5fHfe

[PatM]

Too much glue and/or  glue with diminished elastic properties, for whatever reason.

 Switch to Knox and your problems will go away.

[osage outlaw]

What glue did you use?

[chamookman]

What Pat said . Bob

[Stick Bender]

I had one due that when I hung it 6 ft above a heater vent curing to fast !

[gutpile]

agree glue issue..gut

[hoosierf]

That happens in the winter in WI. I’m in Green Bay and the only bows that do that are the ones I’ve sinewed in the winter. Sand it down with something below 100 grit then 180 grit then cover it with a few thin coats of titebond. Don’t go crazy with the sanding just give it a quick work over and make it smooth to run your finger over. I think it will survive those aren’t that bad. No guarantees but I wouldn’t give up on it.  You won’t get all of the cracks out. You are opening up the surface and ideally forcing some PVA glue into them. A lot will disappear.

[ajbruggink]

That happens in the winter in WI. I’m in Green Bay and the only bows that do that are the ones I’ve sinewed in the winter. Sand it down with something below 100 grit then 180 grit then cover it with a few thin coats of titebond. Don’t go crazy with the sanding just give it a quick work over and make it smooth to run your finger over. I think it will survive those aren’t that bad. No guarantees but I wouldn’t give up on it.  You won’t get all of the cracks out. You are opening up the surface and ideally forcing some PVA glue into them. A lot will disappear.

What if I plan to put more sinew on a later date? Will I still want put titebond glue over that?

[PatM]

   My recommendation would be to soak it off and re-apply it properly with better glue.

[bradsmith2010]

I have had those cracks before,,and the bow did not fail..
 Pat may be right that soaking it off and re doing it would be the best,,
but sometimes i think the cracks are just in the glue,, and not effecting the sinew,,
if you plan on putting more sinew,, the titebond might not be necessary,, but I have not tried it with titebond so am just spit balling,,

[hoosierf]

I would not sinew over titebond. If you want to add more sinew I’d do the sanding routine now and wait for more humidity in the spring for your next layer.

I always use PVA glue to seal my sinew backs after they cure and only after the last layer. When you put down the next layer layer I would tack up the back with a warm wet rag.

I think the outer hide glue exposed to dry air gets hard but the glue down in the matrix is not fully cure so it’s like an egg shell.  When it cracks the moisture escapes, it cures down inside, and it seems to work ok. It’s just not attractive.

[ajbruggink]

What glue did you use?

I used hide glue that I bought from Pine Hollow Longbows several years ago

[PatM]

 Commercial hide glue can be hit or miss as to the quality.   I've had it where it was obviously rendered from partially decayed hides.  Fine for a static application but no use for flexing and stretching.
 
 Never had a problem with food grade.

 Mike is or was a TB guy so he may not know how his glue is actually working in this application.

[bradsmith2010]

Pat do you think the Knox is the best overall solution,, I have some hide glue , but am thinking of trying that,,knox

[PatM]

 It seems the most reliable short of experimenting with the best commercial stuff you can get your hands on or making your own in a controlled process.

 Knox has to be made from quality  material to meet food standards  and the extraction process isn't just boiling.  I believe the method extracts the collagen in a relatively less destructive process than heat.

 Marc has even mentioned liking another brand (Davis) better than Knox but I've never seen it in stores here.