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Bubbles in sinew backing?
Marin:
--- Quote from: superdav95 on June 12, 2023, 03:21:08 pm ---Looks to me that this may be an issue only with your last layer. Are you doing one solid layer or several layers and letting each dry well before the next layer. I like to scuff between layer personally and depending on the bow or project aim I’ll do 2 or 3 layers letting each dry well. I put a good layer of glue prior to next layer. It could be you’ve starved it of glue between layers perhaps??? Just a theory…. You sinew looks pretty clean to me this being said. I don’t foresee any performance issues. Here’s a couple pics of my latest sinew. It’s been drying for a few months now just almost ready to start going on it. It’s ready and dry now but I’m giving it lots of extra time. You’ll see that it has some lighter coloured inclusions and not totally amber in Color. This is normal for sinew. Help this helps.
--- End quote ---
Yeah this is an issue I have seen priamrily with this layer. It did occur a little bit here and there for the previous layers.
I do usually try to do the layers searate, but usally give myself about a day or two in between applications. Usually I have to wait longer since I need to process more sinew (I apply my layers thicker, with bundles of about 30 strands of sinew or more).
In the case of this "layer" this was actually the crowning layer (so a thick strip of sinew going down the center of the back) for the second layer on this bow, which was ideally supposed to be the last, and I had put the full second layer on only a couple days ago so it had some time to try. I do usually try to sand and roughen up layers before putting on a "sealing" layer of glue in between applications, but for this crowning layer/strip I did not do that, so perhaps that played a part.
I'm going to sand and put a final layer of sealing glue on it tonight and since it appears most of these bubbles are shallow, I'm hoping that fixes it. For the deeper bubbles, I'm just going to cross my fingers that these doesn't lead to future problems.
So as long as the bubbles don't appear or sound like they are compromising the backing (like with crunching or popping sounds when I press) I should be fine?
Marin:
Also, do you guys think maybe adding too much glue could be a potential cause? I notice that I tend to add glue pretty liberally, not only dipping the bundle in glue and not squeezing it but dabbing my finger in the glue pot and rubbing that on the strip once it has been laid flat. I always thought it was better to be more liberal in the adding of glue so you can avoid not adding enough, but now I am wondering if that is the cause.
superdav95:
I had heard a general rule of equal weight of sinew to glue. I pound and separate my sinew dry and then comb it dry with wire brushes. I weight it all in layers per limb. I then soak it in warm water overnight in seperate bowls in the pre weighted bundles. Next day I wash it with dawn soap really well and put it back in clean water. I prepare my glue using a glue pot and use granular hide glue. I’m not a fan of the Knox gelitan as glue. I’ve had mediocre results with Knox glue. I know a lot of guys have good luck with it but my personal opinion. I use 30-40% by volume glue to water as my mix for laying down the bundles. Prior to doing any of the above I size the back of the bow and score it before laying sinew. Sizing is vitally important in my opinion. I do about 7-8 or more size coats with very thin hide glue. Pretty much water with a little glue. This allows the watery thin glue to seep down into the wood pours of the back of the bow. This ensures good adhesion. When sizing is done and ready to lay the bundles I take my bundle out of the water it soaks in and squeeze out as much water I can with fingers then dunk it in the hot hide glue squeezing out the excess then dunk again doing the same and lay it down and smooth it out. I also put a good fresh coat of glue down just prior to laying bundle down. Hope this helps. I’m sure there are lots of ways to do this but this is basically how I do it. A little heat when sizing the bow is also good idea too. Best of luck.
Marin:
Thanks I'll keep this in mind,
I guess I have only been soaking the sinew but I never would have thought to wash sinew even with dawn dish soap.
So just to follow up on what you said earlier, you don't think these bubbles will provide any issues? Like are bubbles only of concern when they are pretty big and between the sinew and wood?
Pat B:
If you read the info I posted while I was building "Elg Bue" the copy of an ancient Danish bow that I added a sinew backing I went through my process for prepping the sinew and the bow's back...basically I soak then wash the sinew in warm water and Dawn dish soap and rinse it with warm water. Then I scrub the back of the bow with Dawn and rinse with boiling water. I do these preps just before I start the sizing coats then continue by adding the sinew to the back of the bow. I like to start the sizing and sinewing while the back is still damp so I'm sure the sizing coats soak into the wood.
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