horn delaminated after sinew
I just finished putting the first layer of sinew on a composite bow (deer sinew, bamboo, and gemsbok horn). After drying for 3 days, I was surprised to find that bamboo-horn joint had slightly separated in several places, mostly in the middle of the limb and on one side. The bamboo appears to have been lifted off of the horn due to the sinew. See the pictures linked below. The glue I used was a mixture of hide glue (gelatin powder) and fish glue, both previously tested for strength. Before adding sinew, I had also bent the limbs back approximately to stringing position to check the tiller and there were no problems then. Here are some possible errors that might have caused this:
1) I forgot to add reflex with a string before adding sinew and did that right after. It was no more than 1-3 inches. I smoothed down the sinew with a bit more glue after this to make sure it didn't pop up.
2) I kept the bow outside to dry in the sun. This may have caused it to dry to quickly or possibly the high heat caused stress by causing some parts to expand more than others.
3) The glue joint was exposed to water when I washed the back surface with dissolved wood ash to degrease. However, it wasn't very much exposure.
4) I added a small amount cornstarch to the glue used to glue the horn in order to enhance its space-filling ability.
It looks like I will have no choice but to take off the horn and glue it back on. Any tips on how to do this and prevent this problem in the future?
Thanks
https://i.gyazo.com/1842f396aa1a8eec821 ... ba7006.jpg
https://i.gyazo.com/631ac153b6d5fd70f6c ... ef2f7f.jpg
1) I forgot to add reflex with a string before adding sinew and did that right after. It was no more than 1-3 inches. I smoothed down the sinew with a bit more glue after this to make sure it didn't pop up.
2) I kept the bow outside to dry in the sun. This may have caused it to dry to quickly or possibly the high heat caused stress by causing some parts to expand more than others.
3) The glue joint was exposed to water when I washed the back surface with dissolved wood ash to degrease. However, it wasn't very much exposure.
4) I added a small amount cornstarch to the glue used to glue the horn in order to enhance its space-filling ability.
It looks like I will have no choice but to take off the horn and glue it back on. Any tips on how to do this and prevent this problem in the future?
Thanks
https://i.gyazo.com/1842f396aa1a8eec821 ... ba7006.jpg
https://i.gyazo.com/631ac153b6d5fd70f6c ... ef2f7f.jpg
probably a bad reply but... did you apply sizing coats? slowly try to tie the ears into reflex? (though that may've actually made it easier for the horn to separate.. should also wrap in elastic waistband or something)
Yes I applied sizing for both horn and sinew gluing.
I would say error no. 2 & 3 is the main cause for the de-lamination.. heat + damp would make the glue melt.. imo
If sinewing made the horn separate from the core, I feel the glue joint must somehowe have been weak.
How did you clamp horn to core? Enough pressure? Even pressure all along the horn? How long did you let it cure before adding sinew? If it did not cure long enough, then A. Haydars answer is all the more probable. I'm not at all sure adding corn starch is a good idea, hide glue has some space-filling properties on it's own.
How did you clamp horn to core? Enough pressure? Even pressure all along the horn? How long did you let it cure before adding sinew? If it did not cure long enough, then A. Haydars answer is all the more probable. I'm not at all sure adding corn starch is a good idea, hide glue has some space-filling properties on it's own.
I used clamps and rope to apply pressure. The horn was glued several months before the sinew was added. Before adding sinew, I did bend the limbs quite a lot back to about stringing position to test tillering and there were no breaks or cracks. I would guess that this puts more stress on the glue joint than sinew drying, which contradicts the weak glue explanation, but maybe unevenness in the sinew put extreme stress on certain areas and not others.