Sinew back questions

[Gote]

Hi I have a question regarding sinew backing of bows.   I finished my first bow a couple months ago. It's a birch flat bow with a sinew backing.  After shooting for a bit I've been finding more and more of the sinew fibre ends beginning to lift.  How can I stop this and how can I prevent it on my next bow.  To finish the bow I put a thin layer of hide glue over the sinew and when cured I spayed a couple coats of polyurethane to seal everything.
Thanks

[osage outlaw]

Did you clean and degrease the back of the bow before backing it?  Did you size the back first?

[PatM]

Sounds more like the sinew is separating from its matrix than the back.

[Gote]

Sorry I'll try to clarify a bit better.   The sinew is holding fine to the wood.  It's just the tips of the individual fibres that are beginning to lift off the sinew beneath them on the outer surface only.   I'm thinking it has something to do with my glueing process or the glue.  As the bow flexes it's made small  lateral cracks across the sinew.  From what I've read this may be an indication of too much glue.   I think that it's where these little cracks coincide with where a sinew fiber ends that allows it to lift.

Could allowing one layer to dry too much before applying the next cause lifting?

[mikekeswick]

Don't worry about the whitelines.
The reason is likely that your glue wasn't concentrated enough. You want to use the same weight of dry glue as the amount of sinew you are using. Mix that glue with water to give you a 20 - 25% solution.

[bradsmith2010]

if you are doing one layer and letting it dry,, it is a good idea to size the dry layer before applying more,,also as suggested,, you may not have soaked the sinew in glue long enough before adding or your glues was a little weak,, too much water,, but next time rough up the sinew a bit and size,, and I bet that makes a better surface for the next layer of sinew

[Gote]

it is a good idea to size the dry layer before applying more

What do you mean by sizing the layer?

Amongst other mistakes, I think you're right about not soaking the sinew long enough.   I shortened my soaking time because I found the sinew just shrivelled up and was difficult to apply.  Is there any way to avoid the shrivelling sinew?

[mikekeswick]

You had it far too hot then. 50 degs max.

[Marc St Louis]

Sizing is the term used for applying a coat of glue to the surface.  If you're letting the glue dry then it's also a good idea to wash the back before applying another layer.  I always apply all the sinew in one go.

[JoJoDapyro]

HAHA, did it look like Ramen noodles? I did this the first time the other night.

[Gordon]

What Mike said - your glue was too hot. The sinew should not shrivel.

[Gote]

HAHA, did it look like Ramen noodles? I did this the first time the other night.

Seemed like it would only happen to the last couple inches of one end of the sinew.  Don't know why.

Anyways thanks for all the feedback.

[mikekeswick]

Because the ends get more heat to them quickly and they are thinner.