Sinew Troubles

[SLIMBOB]

Thanks for all the help guys...Dunno...I feel like the back was prepared well.  I didn't use boiling water to clean it, just hot tap water.  Dish soap and a scotch brite pad.  I will use boiling water next time.  Pat...not tight on the Vet Wrap, just snug and laid neatly side to side.  I applied the sinew Saturday night.  Set it wrapped in the sun (upper 80's) about 2 pm.  Was that too soon?  I noticed something odd about the glue.  I made 2 batches (now 3).  The 2nd batch (different box) didn't seem to gel as quickly as I am used to.  Didn't think too much of it at the time.  Any way, I just followed the advice here and worked on patching it with a fresh batch of glue.  We shall see if it holds.  Just for piece of mind I wrapped both areas to hold it down.
Third batch gelled on schedule.  Just checked it. 

[DC]

Is it possible, with hide glue lifting like this to just inject a little water to soften the glue and then clamp it and let it re jell?

[SLIMBOB]

I think in essence that's what I have done.  I just used warm hide glue instead of straight water.  I lifted the sinew as much as I could after wetting it with a hot wet towel and letting it set for about 20 minutes.  I got the glue underneath the sinew as best I could, layed down a little fresh sinew to close up the hole, and wrapped it. 

[DC]

I guess glue would be better. I was thinking water is thinner and would sneak into the ends of the crack/ separation.

[PatM]

When you wrap with vetwrap after the outside starts drying you  should be wrapping as tightly as possible and doubling up on the overlap.   That would have allowed you to safely place it in the sun because it would be firmly pressed into place with no room to raise up even if it temporarily liquefied.

[PatM]

Smoother, tighter and more optimized glue percentage.  The same way modern composite materials like glass and carbon use the same idea.  It doesn't leave " ugly stripes" if done correctly.

 Many people have wrapped sinew backings in the past.

How the wraping can optimize glue percentage if You wrap geled glue ?

  If you read the how to you will have your questions answered.

[SLIMBOB]

You have a good point, water being more viscous...or is it less viscous...more liquidy.
Pat...I had Vet wrap here, so I used it instead.  I had read that you had started using it as well instead of the inner tubes.  The vet wrap is far more stretchy than the inner tube, so I just got it snug, no overlap.  I will change that next trip.  I will also say that this didn't seem to appear until after the Vet wrap.  Could be it was loose already I just hadn't noticed it yet. I still believe something was odd about that glue that could be the culprit.  I just checked the bowl in the garage and it is still not hardened off.  Not runny but soft.  The glue I made up earlier today is nearly as hard as this.  Granted its been in the garage and warm but it should have been harder by now I think.

[maitus]

This is one page from Adam Karpowicz book.

 The glue must gel before sinew begins to visibly dry, which is around 2-4 hours depending on the ambient humidity. The gelled,
solid glue holds sinew in its proper place on the bow, not allowing it to shift or pull-off from the core as it dries. With no gelling, the
limbs would require wrapping with something like a bandage or rubber bands. Such devices can either impart an undesirable
texture to the dried sinew or prevent the drying altogether. The Turkish bowyers never did that, on the contrary, Kani wrote bows
were hung close to the ground after sinewing – obviously to take advantage of the cooler air to make the glue gel. In the Korean
method the glue-saturated sinew bundles are put aside wrapped in wet cloth to cool off and gel, before applying to bows. The
Chinese did the sinewing in the winter. According to Taybogha (Syria, 14th c.) bows were sinewed in early spring, again to take
advantage of cold air in the otherwise hot climate. The method by Klopsteg of laying sinew in a “Turkish bath” may have merit,
provided the bow is transferred to a cold room to make the glue gel after the operation is finished. I need not mention the layer of
sinew should be allowed to dry in a temperature well below 35 degrees Celsius, otherwise the glue would liquefy, again
endangering the integrity of the sinew layer.

  To make glue, the same amount of dry weight as sinew is mixed with water for 20-25% concentration. In the dried sinew layer
the glue content ranges from 30 to 50%. Too much glue is not desirable, because it adds dead weight. Too little glue, on the other
hand, weakens the bonding with wood and lowers the cohesion of the layer, resulting in air pockets within it. I sometimes use a bit
more concentrated glue for the first layers and then less concentrated for the last one. In most old bows the sinew layer had the
texture very much like sinew in new bows. In one unfinished bow however, still tied in its pretzel shape, sinew did not even show
the fibrous structure, possibly due to either a very high amount of glue, or the aging process, where sinew “fused” with glue over a
long period of time.

[bradsmith2010]

I have a bow I made bout 20 years ago, I know it was very hot in Texas at that time,,
I probably brought the bow inside to cure in the air condition,,the sinew is still on the bow,, I did find with that bow, that as the sinew cured the draw weight of the bow kept going up,, more than usual,,but did have a positivie outcome and stayed on the bow without any lifting,,I did not wrap the bow,, but just let it cure,,for a couple of weeks and started shooting, it,, not because I thought that was the best,,just because I could not wait to shoot it,, so it seems there can be some slight variation in the process,, with successful outcome,,
the only time I put a sinew bow in the sun,, glue started to oozz out,, so I never did that again,,

[PatM]

Yep, the old Asiatic composite techniques using fish glue and Isinglass are very dogmatic.   That doesn't make them right when it comes to   gelatin glue and innovation with a better understanding of how glues behave when manipulated with heat and pressure.
 
 All of those concerns voiced by Karpowicz are not an issue at all.

[SLIMBOB]

The proof is in the pudding. I may have screwed this one up a bit, but the ones done your way look superior to the “old” way. I can’t comment to which is better yet. But my guess is this way.

[PatM]

Sinew backing definitely can be done as nicely with the  traditional  method.  My idea was simply to arrive at the same results in a manner that was much easier to achieve without necessarily having many practice runs and perfect conditions or exotic  slow gelling bladder glues from endangered fish.

 Many people don't have the sinew volume or facilities to  become skilled through lengthy practice so a shortcut made sense.

[SLIMBOB]

So far as I can tell, the reglue is holding. It’s seems to be any way. I will check it more thoroughly once it has dried. Thanks for the help.

[burchett.donald]

  Bob, I think wrapping those areas and letting them dry is the way to go...Sounds like rapid drying may have caused the pick up?

[SLIMBOB]

Maybe Don. I will do a few things different next time. I think it’s holding, best I can tell.