Sinew - Melting it Onto the Core?
I know you are supposed to throughly size the core with thin glue such taht it gets as deep as possible. And I have seen the process whereby the sinew layer is applied, and then heat is applied to get the sinew to stick. How important is this melting step? Would not a moistened sinew strip, melt into the sized limb by the moisture it carreis with it? Or is this not enough to get proper adhesion to the glue layer on the sized core?
'Melting' does not imply melting of the sinew itself. The temperature of the glue should not be greater than you can comfortably handle with your bare hands.
After having well-sized surfaces, you need to avoid two risks: getting grease on the surfaces and the formation of bubbles, either of which would undermine the limb's strength once the glue sets.
As regards the melting of the glue: the consistency of the glue should not be too thick, otherwise the risk of retaining air bubbles increases. Do not stir the hot glue vigorously otherwise there will be more bubbles. The glue should heat to just below boiling point so that any air can bubble off, then be allowed to drop in temperature without stirring.
After having well-sized surfaces, you need to avoid two risks: getting grease on the surfaces and the formation of bubbles, either of which would undermine the limb's strength once the glue sets.
As regards the melting of the glue: the consistency of the glue should not be too thick, otherwise the risk of retaining air bubbles increases. Do not stir the hot glue vigorously otherwise there will be more bubbles. The glue should heat to just below boiling point so that any air can bubble off, then be allowed to drop in temperature without stirring.
I've done well at avoiding air bubbles, and I use lukewarm glue so I've not had problems with denaturation of sinew or anything of that nature. I was just curious about how the sinew strip would adhere to the heavily sized core surface, and whether or not heat is required to melt the sized surface a bit and allow the sinew to "sink in" a bit. Although I suspect that the moisture in the sinew, would cause the sizing to become sticky enough that you'd get good adhesion.
Lennie; When in doubt, do a small sample. They say that technique does not count but my thinking is that technique is everything. When I saw the korean bowmaker video and he would heat the limb which had been coated repeatedly with glue, I tried this. Seems as though all the previous layers of glue can be activated with heat and moisture. But my experiments have also shown that this is a function of temperature. When done in warm weather, the moisture alone activates all the layers. You want enough pastey glue at glue-up to fill all voids and extrude out just a little as proof.
There is also the factor of setup time. In cold weather, the setup time seems greatly reduced (the time which the glued piece can be worked) In warm weather, the working time seems longer. My conclusion: korea is colder than South Texas, so heat is required to activate all the glue layers. I should add that I am using pearl glue from Europe, I assume that this is hide glue of cattle, but have recently started adding a small amount of fish glue to extend the working time- it does. This is for the horn and wood parts only, pearl glue alone is even excessively perfect for sinew.
I might add that all my bows are experimental and not noteworthy, but pearl glue has proved to be strong, flexible, cheap and not the source of my problems. Is this helpful? -j-
There is also the factor of setup time. In cold weather, the setup time seems greatly reduced (the time which the glued piece can be worked) In warm weather, the working time seems longer. My conclusion: korea is colder than South Texas, so heat is required to activate all the glue layers. I should add that I am using pearl glue from Europe, I assume that this is hide glue of cattle, but have recently started adding a small amount of fish glue to extend the working time- it does. This is for the horn and wood parts only, pearl glue alone is even excessively perfect for sinew.
I might add that all my bows are experimental and not noteworthy, but pearl glue has proved to be strong, flexible, cheap and not the source of my problems. Is this helpful? -j-
It does make sense to me that heat might only be needed in certain circumstances. My gelatin glue is nicely solid at room temp (70-80F), even being moist. I think there might be some benefit to using a mild heat to set things in better. Adding some fish glue would probably be an alternative.
Thanks for the input, that was helpful.
Thanks for the input, that was helpful.
Sorry Tom that I missed your point. Yes, the Chinese bowyer heats the sized core before adding sinew. But the purpose again is to drive off air and prevent the formation of bubbles, not to 'melt' the size'.
When you add the glued sinew, you want to have pre-heated air in the fissures in the surface (that cannot be completely eliminated) so that any air will contract on cooling. If not, the warm glue will cause the cool air to expand when the sinew contacts it, weakening the bond.
It's the same idea as when you use hot melt to put a bullet head into an aluminum arrow shaft and you heat the shaft first.
When you add the glued sinew, you want to have pre-heated air in the fissures in the surface (that cannot be completely eliminated) so that any air will contract on cooling. If not, the warm glue will cause the cool air to expand when the sinew contacts it, weakening the bond.
It's the same idea as when you use hot melt to put a bullet head into an aluminum arrow shaft and you heat the shaft first.
Excellent explanation. I am slowly starting to see how air bubbles are a real enemy of a good glue bond. Thanks.