Here is a photograph of my attempt at a composite bow. It shows the bow limb in the siyah splice section, where there is a lamination of maple. As can be seen the glue here has failed. It was water proof PVA. It failed directly after sinewing the bending limbs only, this being the third layer of sinew. Two total layers had gone on before. I have not bound the limbs closer together after each layer of sinew, not wanting a fully C shaped bow.
I think that the shrinking sinew must have pulled up the lamination, causing failure. My question is this, how could I have averted this catastrophe?
Regards
Redhorse
There is no glue like hide glue.
M Hardman
Alas, I fear that might be the truth, I regret making the core as I did.
Redhorse
I never use water proof glue. Hide glue can be removed with water or heat. You can even take of the horn strips if they are glued with hide glue. You can try with heat to open the glue line but you have to redo the sinew there.
Stephen Selby
There must be absorbtion of glue into the limbs to get the effect needed. I am sure that a waterproof glue would cause problems. As I have said elsewhere, good hornbows are basically made of glue.
S
Hartung
M Hardman wrote:
Dear All,
My question is this, how could I have averted this catastrophe?
Regards
Hi there! I have no clue about building horn bows but ? other then self bows ? I have build about a dozen of all wood laminated long bows and recurves. Most of them had up to six layers of wood laminations with a final backing made of bamboo. All of the laminations where glued with simple carpenters glue (white glue), similar to the one you used. Maximum power was 70#. I had only one failure which was my fault.
In order to avoid any errors I talked to the company that made this glue and they gave me very precious information one of which is that if the glue line fails, it is your mistake. If the wood fails (breaks) it is the wood that is to blame. If the glue is applied properly it will ?never? fail for the simple reason that its adhesive strength is many times stronger than the adhesive strength of the wood fibres.
There are many possible mistakes you could have made so that I don?t want to engage in any speculation. What I?d do is get a technical date sheet concerning the glue and also one about gluing techniques and study them carefully. Most of the time you?ll rapidly realise on your own where the error was made.
I?d say that glueing techniques, no matter if hide glue or others, must be studied just as well as any other bow making technique. God luck with it!
jkekoni
If the glue is applied properly it will ?never? fail for the simple reason that its adhesive strength is many times stronger than the adhesive strength of the wood fibres.
yes, and when it fails it will not fail at the joint, but 0.1-0.5mm away from it.
M Hardman
You are quite correct, my PVA gluing technique could be at fault. I have had problems with it in the past. Hide glue only in the future!
I wondered if the problem was that I'd sinewed only one section of the limb, or that I'd not bound the limbs closer together. Would the above two factors be a problem normally?
I find it quite a shame, the bow seems workable in its other respects.
Adam Karpowicz
Mike
Did you use PVA = polyvinyl acetate or the yellow carpenter's glue? These are different glues - PVA does not have enough stiffness (hardness) and tends to creep, which makes it unsuitable for flexing members. The other one might be OK, although there is more flex in hornbows than in the all-wood laminated bows.
I would try to salvage the bow. If the yellow glue was used, the gap can be flooded with cyanoacrylate glue (Superglue) and clamped, re-flooded etc. until closed. The affected place can be wrapped with sinew. After allowing min 1 month drying time, the bow might work.
Adam
M Hardman
I used the white water proof polyvinyl acetate I'm afraid. The crack shown there is the largest of four, all of which appear on the same place on each limb. I'll use good wood next time, thus removing the need to laminate. The other three cracks can only be detected by seeing where the hide glue clumsily splashed by me cracked.
The crack won't propagate through the limb, as the lamination shown was just put in place to hold the core wood in the non-bending section shape. The ear splice goes halfway down the limb from the ear. Would flooding the cracks with hide glue, then binding work(I'd bind from the ear down to an inch from the end of the spice)? If I used the PVA, it wouldn't penetrate the smaller cracks. Equally hide glue might not adhere to the PVA still in there? Will super glue work with PVA?
Aside from that I have to re-glue a part of the sinew, I was slightly too religiously squeezing it out, and now there are bleached patches.
A further problem is that the limb is a good 5/8 of an inch thick. I'm going to have to tiller it using pulleys. Even when it had only one layer of sinew on, I couldn't even bend it across my knee to straight.
Thanks for your advice
Kyudohund
Hi Mike,
I think you should lay this bow aside for later times, when you got experienced in making hornbows. 5/8 inches thick ..... :shock: !
My advice: build a bow with maximum (!!!!!) 1/2 inch thickness of sal. As thinner the bending part (sal), as less the problems. Don?t mix for one part (f.e. the wooden body) of the bow modern waterresident glue and for the other steps hygroscopic glues like hide-, sinew or fishbladderglue. This cannot work!
And please don?t use superglue! It is on the one side indeed very addesive, on the other not elastic.
Also you can "help" the bow to held with binding it AFTER bringing up one layer of sinew in a more reflex form, because this layer will shrink a lot. After the next layer in a more reflex .........
As I can see on your fotos, one way of making the bow "lighter" and repair it, is scrape down the horn, until the cross-section is finished and bind the hole lenght with sinew like a thread. See in the picture, how I did it partly on my bow.
