Primitive Archer
Main Discussion Area => Bows => Topic started by: sieddy on February 26, 2015, 01:12:26 pm
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Hi all,
I'm planning to back an Elm bow with Jute twine and wood glue. Do I need to wet the bundles of twine before saturating in glue and should I warm the glue?
Thanks :)
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Why do you need to back Elm and why jute of all things?
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To answer your question, I would wet the and then scrunch the moisture out. I think the wet fibers would not be as difficult to work with. Heating the glue? Only a little to lake it runny. And I guess it depends on how cold it is. I am sure that you are backing it with jute cause that's what you have. You could put the stave in reflex and then put the fibers on.
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Hi Pat
the bark was welded onto the stave and when trying to get the thick inner bark off I violated the heck out of the back. I read on here and other places that plant fibres made good backing and I've got loads of jute twine.
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Hi Sasquatch
Thanks- that pretty much confirms the plan I had.
And yes I have got a big roll of Jute twine so thought I'd try it before going out and getting something else. Fingers crossed! :)
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It never hurts to try, but I would comb out the short fibers. See if the twine is made from long or short fibers. Use the longest you can get a good number from.
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Doesn't jute cordage have a wax or oil on it? That might make it not adhere well to the glue.
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Hi Pat
the bark was welded onto the stave and when trying to get the thick inner bark off I violated the heck out of the back. I read on here and other places that plant fibres made good backing and I've got loads of jute twine.
More reading about bark removal techniques less about guys speculating on weak plant fibers as good backing. ;)
Jute is very weak. Try breaking a strand of it.
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Fair point Pat! :o
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I would also remove twist from the jute twine (if any) and comb the fibers to get long fibers. I find that fibers 20-25 cm are ideal. Longer become a bit difficult to manipulate at once.
Jute is indeed a rather weak fiber (so is sisal, which I used recently; I guess PatM is referring to that :P), but it's still stronger per unit of mass than most wood.
I'm not sure i'd use wood glue, but that's just a personal taste. I like to use hide glue or its purer kitchen form: gelatin leaves. Using gelatin soothes the other half (something they can relate to O:))
I would wash the combed fibers in a soapy solution to get rid of the bulk of the impurities before gluing.
After that, rinse the fiber bundles in hot water, let them drip out on a towel (they don't need to be dry) and submerge them in warm hide glue (or wood glue, if you like). Squeeze out the excess, and apply on the back. After finishing the entire bow, I like to wrap the entire bow with inner bicycle tubings to ensure the fibers stick well to the back to squeeze out more of the excess glue.
With hide glue, if you store the bow in a hot place for an hour or so (I hang it above my wood stove, where it's about 70°C / 158°F), the excess glue will be squeezed out very easily.
After a day, I remove the tubing, and when completely dry, I give the back another layer of hide glue. After that's dry, you can apply a more permanent sealing.
good luck with it, anyway you do it
Joachim
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Thanks very much Joachim
That's really helpful- especially the bit about keeping the other half sweet! ;)
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Jute is very weak. Try breaking a strand of it.
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How weak is jute really?
Of plant fibers, flax and hemp are said to be the strongest fibers, yet if you take a narrow strand of flax, you can easily break it. So that's not really a good test. A similar "strand" of osage would break even much faster (see below), yet no one would dare to say that osage wood makes poor bow backs.
It is said that jute is inferior to flax and hemp (e.g., TBB2: strings), but how does that relate to jute as a backing material compared to other fibers, and to other woods (unbacked)?
Suppose you'd elongate a plant/wood fiber by 1% (about the maximum stretch a normal self bow would ever encounter on its back) how much force would you need?
Let's use Osage as the bench mark of strength, the most prized bow wood on this forum, and give it a strength score of 10, so we can compare how other fibers or woods relate to that for a same strand/wood diameter.
Osage: 10
Yew: 8.0
Black locust: 12.1
Lemonwood: 13.5
Ipe: 19.0
Bulletwood: 19.8
strong Flax: 60.1
weak flax: 43.0
Strong hemp: 51.5
Weak hemp: 25.8
Strong jute: 43.0
weak jute: 17.2
high grade Sisal: 18.9
Though not all woods can take 1% elongation, all these plant fibers can. Many will even stretch to 2 or sometimes even 3% (which is still way below what sinew can take, but that's another story).
So in other words, even rather low quality jute fibers will be as strong in tension as the strongest wood (bamboo not considered).
the reason for this is that the actual tensile strength of plant and wood fibers is determined entirely by cellulose. The higher the cellulose content, the stronger the fiber or wood. Flax has the highest cellulose content of any plant fiber (65-85%), Hemp is a bit lower (60-77%), jute even lower (45-63%), just like sisal (50-64%). But that's still more than most woods, which have at most 40-50% cellulose content.
So if decently applied, any OK plant fiber backing will be stronger and more elastic than a wood backing, even fibers generally rated as poor like jute and sisal.
Of all these fibers, it seems that sisal can stretch the furthest in an elastic way (see table 11 in chapter below, making it the most sinew-like).
Source of the plant fiber strength data (and pdf of article available on request):
Lilholt H. and Lawther J.M. Natural organic fibres. In: Comprehensive composite materials, editors: Kelly A. and Zweben C. Vol. 1. New York: Pergamon Press; 2000.
Source of the wood strength data: The wood handbook: wood as an engineering material; www.wood-database.com
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I've backed bows with burlap which is jute and may be a bit of sissal.
Jawge
http://georgeandjoni.home.comcast.net/~georgeandjoni/burlap.html
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If its good enough for you George it's definitely alright by me! :D
That's really interesting Joachim (if nothing else I've learnt alot about natural fibres!) :)
Anyway i'm gonna use plant fibres and gelatine glue as a backing on the poor Elm stave I messed up today and I'll let you all know how I get on.
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Nothing wrong with what you are doing, but you COULD chase down to another ring. And that was a great bit of info from joachimM, too.
I don't see why anyone would want to use ANIMAL based glues on PLANT fibers, though. It'll work, and it's strong. But wood glue is formulated for wood, and jute is going to have WAY more in common with wood than collagen-based animal fibers like sinew or hide.
I would use TB II or III, thin the glue with a tiny bit of water to soak the string, size the back of the bow with thinned glue, and lay down the saoked fibers before the glue on the bow dries completely. Warming wood glue will only make the chemicakl reactions and the drying that cause it to cure to happen faster.
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Well a sinew backing is glued with animal glue to "plant" fiber... ;)
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I always used Titebond 2 or 3 on burlap and silk. Well not always. I backed a bow with (animal product) silk and used hide glue. It came off in a rain storm.
Jawge
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Thanks for chipping in Springbuck. I would prefer to chase a ring but they look really thin and I fear it would frustrating in the extreme. I'll think on about the glue. Cheers :)
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Thanks for chipping in Springbuck. I would prefer to chase a ring but they look really thin and I fear it would frustrating in the extreme. I'll think on about the glue. Cheers :)
As far as I understand it, it's not a matter of violating a ring on the back, rather than the angle at which fibers are violated (see also TBB2: board bows). So the thinner the rings, the more safely you can violate a ring. Many thin-ringed yew bows fail to follow a single sapwood ring entirely
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As it happens I don't think I've cut through to the heartwood. But still think I'll back it as insurance!
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I don't see why anyone would want to use ANIMAL based glues on PLANT fibers, though. It'll work, and it's strong. But wood glue is formulated for wood, and jute is going to have WAY more in common with wood than collagen-based animal fibers like sinew or hide.
I'm a bit late with this reply... Had to look it up.
Wood glue, at least regular (eg titebond) is liquid hide glue to which urea was added to keep it liquid and stop it from gelling at room temperature. So essentially, there will be hardly any difference. Hide glue granules or gelatin leaves do have a longer shelf life. Moreover, you can control viscosity and tackiness more by adding granules, reducing the volume (evaporation) or adding water.
But bonding properties are very similar.
J
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That's very interesting Joachim thanks for the Input. :)