Primitive Archer
Main Discussion Area => Bows => Topic started by: tkdHayk on June 16, 2017, 05:55:32 pm
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Bow Length: 40 inches
Wood: Red oak
Backing: 3 layers of Sinew/Hide Glue (1.5mm thick). Each layer of sinew had 1-2 weeks of drying time.
(http://imgur.com/qrNbxnJ)
crossbow stock:
(http://imgur.com/d80lyKb)
Required Draw length: 15.5 inches
Desired draw weight: at least 65# at 15.5 inches
As I floor tiller the bow, I hear cracking , and then notice that the hide glue has cracks in it which are perpendicular to the length of the bow.
http://imgur.com/Nh91Wk7
Should I be worried? I poured excess glue on to the bow after applying each layer of sinew. the glue was relative tick. I could re heat and smear/flatter the hide glue to remove the cracks. or I could just ignore it and proceed with bracing the bow, since the sinew itself seems unaffected and is unlikely to fail. What do you think?
UPDATE: I added an extra layer of sinew, using less hide glue than I did on
the other layers. The bow has been brace: http://imgur.com/nNaOqmr
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It is probably just the glue. Too much glue can do that. Generally the only harm it causes is an uneasy feeling when heard. It does add excess physical weight which can inhibit the bow's action.
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It is probably just the glue. Too much glue can do that. Generally the only harm it causes is an uneasy feeling when heard. It does add excess physical weight which can inhibit the bow's action.
I hope so! the excess glue will probably shrink some as is dehydrates further. PS, can you see all 3 of my images? not sure why only 1 of them got uploaded.
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could it be that the glue was heated too much?
The hornbowyer Beaumont Vance in the Facebook hornbowyers, atarn groups has written about how he avoids precisely this cracking problem. Basically, he first sizes the wood many times with thin fish bladder glue, then uses very thick hide glue with the sinew...
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could it be that the glue was heated too much?
The hornbowyer Beaumont Vance in the Facebook hornbowyers, atarn groups has written about how he avoids precisely this cracking problem. Basically, he first sizes the wood many times with thin fish bladder glue, then uses very thick hide glue with the sinew...
I did size my bow with Hide glue (not fish glue). I wonder what difference it makes. When the cracks happened, I was floor tillering in the sun, so it may be that the glue started to get weak due to the heat. How does hide glue generally hold up to dry heat?
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Too much glue and perhaps poor quality glue.
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You said you poured the extra glue over the sinew. That right there is too much glue.
When I add sinew I first wash the bow with Dawn soap and rinse with boiling water. I also wash the sinew with Dawn and rinse with warm water. This cleans the back well and preps the wood to help the hide glue adhere. I them size the bow with a couple of thin brushings of hide glue then begin adding the sinew. I like moistened sinew before going in the warm hide glue, squeegee off the excess glue with my fingers and lay it down. That is all the glue I use, just enough to saturate the sinew then squeeze most out and lay it down.
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It is not too much glue - it is too concentrated glue.
It has to be over 40% solution to start making the cracking noises. Next time just be more careful about how much glue to water you use. 30 - 35% is as concentrated as you ever need to go. Nothing to do with sizing or the extra glue you poured over. Unfortunately it will continue to make these noises when you haven't used it for a while. Nothing you can do about it now other than soak the sinew off and try again - or live with it ;)
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Maybe picture files too big?
Del
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I remember the first few sinew backed bows cracking across the back like this. I was eager to get the sinew on and rushed through processing the fibers as well as laying on the bundles. I ended up with gnarly, ropey, nasty sinew. There were fissures and low spots that I thought I would fill with hide glue. So, I used the stuff like plaster to fill everything in.
BAD mistake. Any job it did was merely cosmetic, a bad sinew job is a bad sinew job. The excess glue does not have the strength of the sinew and it will crack. My lessons learned: 1) process the sinew into thread like fibers 2) smaller bundles, well hydrated, and combed straight so all fibers are parallel. 3) work the glue into the fiber bundles,and then gently squeeze it out - I needed far less glue than I thought.
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I have had the glue make cracks ,, even when I thought I was very careful,, the bow didnt make noise,, and held up fine, but I could see some sideways cracks in the glue,, I think alot of times we cover or paint the sinew,, so it is not noticeable,, :NN
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As long as the sinew does'nt lift or tear or something like that.That's a bond issue then.Don't see that happening here.The way it is now you'll just have to put up with it but feel as though it is safe yet.
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I've never found glue/water ratio made any difference to cracking or not. It all dries to about 90% or so glue. What a higher initial ratio will give you is potentially more total glue left over which is where people run into cracking problems as many have noted.
Thick glue well squeezed out to the optimum glue/sinew ratio doesn't make cracking noises.
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I've had a few sinew backed bows do that. After the hide glue is fully cured. Sand it with 180 grit and then "size" or seal it with a layer of Elmers Maxx or Titebond. The Maxx which I prefer often gives it a reddish hue when I've done this and it's kinda cool. The cracks become almost completely invisible. It's a reasonable way to save the appearance. I doubt the performance is impacted at this point.
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Greetings bowyers,
Interesting and somewhat contradictory responses guys, thank you. To clarify a couple of things:
-I am not concerned with the bow's appearance. The cracks are very small and the bow is very beautiful and smells amazing.
-I don't know if you guys got the up close photo of the cracks, here it is: http://imgur.com/Nh91Wk7
-Perhaps I have indeed used "too much" hide glue, or too high of a Glue/Water ratio. But my question is A) should I be worried about the tensile capability of my backing? Could a sudden crack in hide glue travel down and crack the sinew? Sort of like how an object is easier to shatter when it is surrounded by ice. Is that the case at all? Because If the cracks don't cause the backing to fail, I'll keep pouring extra glue for maximum adhesion. I don't mind cracks if they do not undermine the structural integrity of the bow. what be your thoughts?
Hayk
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I've never found glue/water ratio made any difference to cracking or not. It all dries to about 90% or so glue. What a higher initial ratio will give you is potentially more total glue left over which is where people run into cracking problems as many have noted.
Thick glue well squeezed out to the optimum glue/sinew ratio doesn't make cracking noises.
hey Pat, do you see any disadvantage to using too much glue, as I have on this bow? Can using too much hide glue cause a sinew backing to fail?
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If it's cracking the structural integrity is being compromised. Any time you make a composite material the idea is for both materials to do their part.
So whatever is causing the cracking is the start of failure.
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If it's cracking the structural integrity is being compromised. Any time you make a composite material the idea is for both materials to do their part.
So whatever is causing the cracking is the start of failure.
What do you think I should I do at this point? Add some backing to the glue? wet the glue and smudge off the excess glue and erase cracks? continue as if everything is cool?
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Pat, is it to late to wrap it and heat it to get rid of the excess?
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Yes. It needs to have moisture to flow. I would just soak it off and re-do it.
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Pat, is it to late to wrap it and heat it to get rid of the excess?
Wrap it with what?
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Yes. It needs to have moisture to flow. I would just soak it off and re-do it.
what need to have moisture to flow?
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I was asking if this method would work after it was cured.
http://www.primitivearcher.com/smf/index.php/topic,43246.0.html
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I was asking if this method would work after it was cured.
http://www.primitivearcher.com/smf/index.php/topic,43246.0.html
that clarifies thanks. I could re heat and add water, then use that technique, but that would dilute my glue too much. I think the best solution at this point is to add an extra layer of sinew, using less glue than before. the added heat and moisture form the sinew application process will cause the hide glue cracks to liquify. Plus, it will give me more confidence in drawing this bow. I dont think cracks in the glue will cause sinew to fail because sinew resists much more tension than glue, without breaking.
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tkdHayk...The picture does not show the cracks to be that deep.I think you will be ok.Especially doing the extra what you stated too.I've seen little cross cracks on a sinewed bow of mine before too that is still shooting fine.
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tkdHayk...The picture does not show the cracks to be that deep.I think you will be ok.Especially doing the extra what you stated too.I've seen little cross cracks on a sinewed bow of mine before too that is still shooting fine.
I hope so! Just applied another layer of Sinew yesterday with thinner glue. After about 1-2 weeks I should have the bow braced!
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Bow has been strung!
let me know what you think of the tiller. I'm now aiming for 15 inch draw at 70-90#
also wondering if I should cover the cracks in the glue with superglue? good idea? or will the superglue damage/burn the sinew/hide glue?
http://imgur.com/nNaOqmr
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Less than a week of drying time?
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Less than a week of drying time?
Yup, the previous 3 layers had about 1-2 weeks of drying time, this 4th layer had minimal application of glue, so minimal moisture re introduced to the underlying layers of sinew.
Super glue good or bad idea?
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What sort of cracks do you have now?
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What sort of cracks do you have now?
Same type as before, roughly the same amount as before. the cracks are about 3 mm in length, perpendicular to the length of the bow, and an unknown depth. But I'm guessing they are less than 1mm deep. And the cracks are on the glue rather than the sinew itself, thought its hard to tell for sure.
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Your glue has to be sub par. Switch to gelatin.
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I don't know about the cracks, but I would not use superglue. It looks to me, from the close up pic on page 1, that you didn't break the strands of sinew apart fully, like they are still connected too much at the ends. I've tried keeping sinew strands thick and found they do not sit down well when drying. Better for me was to tear the sinew into as fine a strand as possible, like horse hair. It will comb out and lay down better.
I don't measure anything but I pour a pile of hide glue into a cold crock pot and start adding water while stirring. When it gets thick like something like thick yogurt--not peanut butter, I let it sit for 20 mins and then put the crock pot on 'warm'. Eventually I turn the crock pot up to 'high' and stir and look at it and judge whether I want a little more water or not. It will thin when hot, of course, but you want to be able to grab your bundles of sinew out of the glue and have the glue drip off, like you're dipping in paint...not so thick that you have to scrape it off.
I have a thermometer in and out of there at times and I don't let it go over about 170F, ever, and try to keep it around 140F when I put the sinew in.
I've never done more than one layer so I can't speak to when/how to do the other layers but I would let my stave sit for at least 3 weeks, in any kind of conditions, before stressing it. I might remove excess sinew from the sides or whatever, before that, but no stress.
If you skipped any of my steps I would blame that for the cracking, otherwise I would blame the glue itself. Because I don't like your thick sinew and because of the multiple layers and the cracking, I would start over. If you don't really care that much about this bow then I might shoot the crap out of it and see what happens.
s