Quick question about sinew

[stuckinthemud]

I put down a layer of sinew using gelatine glue about 3pm but stuff got in the way and I didn’t wrap it til just now, about 7 hours later.  This is the first of 3 layers so I’m not stressed as I can fix any problems with the next layer.  Just wondering for another time, is 7 hours too long, and, how long do I wait to put on the next layer?

[Kidder]

The couple times I’ve done it I’ve always let the sinew completely dry (a couple weeks) between layers.

[superdav95]

As long as the reflex isn’t too extreme and is fairly mild then no rush to wrap it.  I only wrap for more extreme reflex bows.  Like kidder said wait two weeks for a safe margin between layers.  It’s not too late to wrap it if you wish to. Keep us posted

[stuckinthemud]

Thanks, will do.  I mostly wrapped it because I wasn’t too happy with how one or two strands were laying.  Two weeks? Will have to learn patience!

[Pat B]

I think you could add another layer of sinew now that might help correct the problem then wrap it. I usually only wrap until the glue gels well(about an hour or so) them remove the wrap. If I have a reflexed back or recurves I will leave the wrap on longer so it doesn't pull away from the curve while drying.

[WhistlingBadger]

So I've heard the "let it dry a week between layers" method, and I've heard the "get all the layers on then dry the whole thing out for a really long time" method.  The latter one actually makes more sense to me, since subsequent layers are going to re-moisten the previous layers.  Any thoughts on that?  I've got a couple juniper kids' bows about ready to sinew and I'm pondering how to get it done.

[superdav95]

WB.  The sinew layers of 2 or 3 layers with allowing each layer to dry for 2 weeks will actually save drying time considerably.  One big fat layer will take 6 months minimum  or more depending on humidity and conditions and such.  The last bow I did in layers only took me 2 months before it was dry enough to start bending it some.  I ended up waiting 10 weeks in the end to get it covered, sealed up and finished.  So in essence it saves time but not only this,  it also helps in quality control of your layers of sinew as each one dries you can see any issues the come up whereas with one big thick layer you may not see buried issues or voids and lifts/delaminating.  It’s comforting to see a good solid first layer as thin as it may be to solidly adhere well to your bow wood.  It’s provides a great foundation for the next 2 layers if that makes sense.  This is just my opinion and there may be some that will say one heavy layer is better.  In my observation and experience with several sinew bows now is that is not the case.   The issues I’ve had with sinew in my builds have been on the one big layer builds.  Often I would see the top portion of the sinew exposed to the air would dry much quicker then the fibers underneath and cause air pockets and voids or lifts from the bow wood.  Even wrapping it would not always fix this issue.  I was able to salvage some but it was hit and miss.  I’ve had much better success with the layers laid in 2 week intervals.  Sinew is not cheap and it takes a lot of prep to get it ready to lay down too.  I got tired of wasting sinew and having to salvage sinew from failed projects.  Just my thoughts on this take it for what’s it’s worth.   

[stuckinthemud]

How do you know when sinew is dry?

[WhistlingBadger]

Superdave, that makes sense.  Thanks for the explanation.

Stuck, excellent next question.

[superdav95]

How do you know when sinew is dry?

Yes it’s a very good question.  I know this answer will likley not satisfy but I let it dry 2 weeks. That’s how I know it’s dry😃  In my climate that’s good and dry.  You’ll notice an amber Color develop after the first week or so almost translucent.  It will be hard and you should see wood underneath the first translucent layer.  I guess you could try a moisture meter to be certain perhaps.  I’ve never done this and find it unnecessary for this.  One thing I’ve noticed as well and this is a little weird but it feels dry and not cool to the touch of that makes sense.  When a damp or slightly damp item is drying it will feel cool to the touch.  Try this out and you’ll feel it. It will be dry to the touch on the surface but still cool to the touch.   Usually by week two it feels room temperature to the touch with my hand.  This is my go to method now.   Another way I’ve done before is by weight. I don’t use this method much anymore but it’s accurate.   I’ll measure before and after sinew.  This can be tricky as there are a lot of parts to include in your weight.  This could in fact be your most definite way to know for sure.  Ive done it before for my first few sinew bows and then stopped as I got a good sense after a while the time line of when it’s dry.  If you weigh before and after sinew remember you have to account for the sinew dry weight then the dry weight of the glue and make note of that before mixing up your glue and soaking your bundles of sinew.  If you use this method after a while you’ll get an idea when it dry.  In my case by the middle of the second week I had gotten within a gram or two of complete water weight loss by drying.  Now some variables come into it but it’s pretty close.  This is a great way to learn actually for your first couple and gives you the confidence in knowing its dry and how long it takes.  So long as you measure everything before in dry weight you should be fine.  It’s a little more hassle but like I say it’s good information to have in the experience bank.  Sinew may seem daunting but it’s worth it I think.   Hope this helps.  Cheers   

[JW_Halverson]

I am gonna jump in and say that two weeks in even a dry climate like mine in the upper great plains is still not enough. Plenty of the moisture from the sinew and hide glue migrates into the wood and until that moisture is out you are just beating your head against the wall.

Get a decent little kitchen scale that weighs down to half grams, tenths would be better. Runs about $20 USD. Weigh the bow every few days and record the weights. When the bow has not lost weight for two to three weeks straight, then I'd say go forward with working on it.

The last bow I sinewed lost the last gram and stayed steady a full month after sinewing was finished and this was a bow I was leaving in the hot South Dakota sun during the day! Being patient never harms anything.

[superdav95]

I am gonna jump in and say that two weeks in even a dry climate like mine in the upper great plains is still not enough. Plenty of the moisture from the sinew and hide glue migrates into the wood and until that moisture is out you are just beating your head against the wall.

Get a decent little kitchen scale that weighs down to half grams, tenths would be better. Runs about $20 USD. Weigh the bow every few days and record the weights. When the bow has not lost weight for two to three weeks straight, then I'd say go forward with working on it.

I would have to agree with this too.  I too would check the weight every few days.  This makes sense and is good practice to follow.  The only thing I’ll say is that for me the 2 weeks was fine for my single layer of 25-30 grams dry weight of sinew for my first layer.  As the second and third layers get added on they will add moisture to the previous layers and may take a little longer then 2 weeks.  It’s a general guide with so many variables. The thicker or heavier the layer of sinew the longer it will take to dry.  I’ve heard tell of guys out there even using a hot box to drive out remaining last bit of moisture too.  Ive not tried this but know some guys do it. 

The last bow I sinewed lost the last gram and stayed steady a full month after sinewing was finished and this was a bow I was leaving in the hot South Dakota sun during the day! Being patient never harms anything.

[stuckinthemud]

I have laid on a second coat, the sinew is not the smoothest coat but I don’t feel the need to fill any gaps with short filling pieces of sinew, so it’s rough but not awful .  Assuming it holds together and I like how it works, can I smooth on a layer of gelatine glue to make a base for a backing, most likely birch bark, but maybe fish skin.  If I did that, what sort of drying time am I looking at for the base layer and also for the backing?

[superdav95]

I would give it a few weeks once you cover with a skin to be sure.  Weight your bow before and after and watch as it stops loosing mass.  Let it sit another week in ac environment in house or hot box too.  Should be ok after few weeks.  Best of luck. 

[bradsmith2010]

Laubins book describes different ways to do it,, its very informative,,