Primitive Archer
Main Discussion Area => Horn Bows => Topic started by: colin1991 on May 18, 2016, 06:19:46 am
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Hi all,
Recently I have been playing around with crossbow designs and had come up with a working design using a laminated timber prod (40" ntn and 120lbs @ 16 inches, 3.5 or so inch brace height) but due to the timber being worked so hard it has failed on me.
Ive seen examples of composite prods for crossbows using a sinew back and laminated horn belly so I though I would incorporate a horn belly onto a timber back and core (either hickory or bamboo as the back and a hardwood as the core most likely.)
My question is, will laminating a series of small sections onto the belly of the bow work if I overlap (cut on an angle and married together) the ends and use a heap of glue, or do the horn pieces need top be full length of the limbs? I would try to get pieces as long as possible for the sake of less joins.
The one example I have seen had very, very small strips (maybe 3-4mm square) all laminated together in the cross section to make up the belly...
Any advice will be very much appreciated.
Colin
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Colin, I think you will be much better off to just butt joint the horn pcs together,.if you lap joint the horn on the belly, then put compression stress on the belly, the pcs will slip one across the other, especially at the high poundages you are looking to attain. I think you will have problems with this happening even when trying to brace the prod, keep in mind if you position the butt splices somewhere in the non working area of the limb you will also have a better chance of success.
I have used the process in the building of my horn composite bows with much success.
post some pics of the prods you have now.
hope this hepls.
james
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Hi James,
Thanks for the information!! I will keep that in mind for my build. Firstly I have to get a hold of a decent quantity of horn.
Another question, probably a hard one to answer but I'll ask it anyway. What kind of thicknesses are the limbs on very heavy horn bows (100lb + ) since I've never built one I have no experience with them and dont know how large or small the limbs will be.
the one prod I have, which is now failed, was basically a miniature English warbow, at 40" ntn. I'd like to keep the new prod the same length or even possibly slightly shorter, since I know horn can take so much more compressive stress than timber.
Cheers,
Colin
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There is no straight forward answer to that question Colin, depends on the material being used, the width, and the length. Among dozens of other things...
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Youcan use multiple strips either side by side or butted along the length. However much easier for you would be to use 2 pieces butted in the center.
Multiply your drawlength by 1.6 to get your necessary width.
You will be safer building it in the traditional way. Horn/maple/sinew. A gentle recurve will aid performance too.
My starting point for thickness would be around 12 - 13mm in the working limbs.
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I don't think it makes sense to leave the back unsinewed, I'd imagine that'd lead to a tension failure. Maybe even with bamboo.. maybe not..
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Thanks for all the info guys, much appreciated!!
I think I will butt them together using as long a strip as I can manage to get. I will keep the limb section quite flat so that should I need to add more horn to get more weight it will be possible.
I would definitely like to use a sinew back on the bow but sadly I dont have any and getting it into Aus could prove difficult. I will hunt around (no pun intended) and try to find a source thats local.
definitely will be adding small recurces and also gluing in a decent bit of reflex to up the,performance.
cheers
Colin
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Hmm, maybe a nylon or polyester cable back could work...
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Go to a butcher shop and see if you can get the leg tendons thats where you get sinew if you can't hunt
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Kangaroo sinew would probably be primo :) :) :) See if you can find a hunter. That is if it's legal to hunt them.
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Thats a great idea!! I will ask around a few local butchers and see if I can get some from them.
I'd like to keep to either a timber or sinew back if possible. I think either bamboo or hickory will hold up fine to the weight I'm after. I've already had hickory to 120lbs in the same design.. If I can get that weight again I'll be stoked!
Colin
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not sure if hickory makes a good core or not (if it absorbs animal glue well?)
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Won't be using hickory as a core and won't be using animal glue for the belly either...
My design will most likely consist of a hickory back, Massaranduba core with small kerfed recurves and a horn belly, All glued in reflex...
massive increases in performance over a full timber prod because of the horn belly, recurves and relflex
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good luck. hm i think someone made a wood bow with a horn belly and no sinew back in the Bows forum? It was pretty long though
I would use animal (hide or fish) glue just based on what I've read from people who've built horn bows, to glue the horn to the wooden core.
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You can use too much reflex with a composite construction as the parts will try to seperate. Think whats happening at the gluelines. Virtuaslly all composites had minimal reflex in the bending sections because of the forces. Study Turkish bows.
Do not use massa for a core it is not suitable. Use hard maple.
It's not about the draw weight as to wether hickory/boo would hold. It's the fact that horn can compress about 8 times further than wood. Sinew is the perfect match as it can be stretched as far as horn can be compressed.
Forget the 'massive increases in performance over a full timber prod...' it is very unlikely that you will see much difference. Composite construction can store more energy for certain but you have to marry the design to the materials capabilities. It's a tricky thing to do and would suggest to you that you have a long road ahead before you get to the potential.
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Ok, for starters, look at the amount of reflex in the limbs of a Turkish bow... You are bending the limbs almost through 90 degrees even before the bow is drawn... I'm talking about using 1-2 inches at either end to create a small curve.
Second, the glue I will be using has never failed on me and I have bows up to 150lbs which are held together using it. It is a structural grade epoxy for use in buildings, joining beams.
As for horn,compressing 8 tines further than wood, are you talking about compressive stress or compressive strain, because there is a massive difference between the 2. I'm aware horn has a massive crushing strength, because of its density and hardness but if it could physically compress 8 times more than wood it would not be any good for a bow because it wouldn't hold any weight.
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Well sounds like you got it all figured out😕 good luck
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Yes indeed look at the reflex on a Turkish bow....where is it? I've made a few and have experienced the problems/heartache through thinking I could just do it how I wanted.
I could save you a lot of problems but as Bubby says looks like you already know what you are going to do! Good luck to ya!
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Is there any curve in the limbs forward away from the direction the Turkish bow is draw when it is un braced, yes. Therefore it has reflex in the limbs. Just looking at photos of your most recent build un braced id say the limbs are reflexed heavily and also recurved slightly at the tips...
No need to say things I want to try WONT work when you have not given any reason as to why... For example, why won't Mass work as a core? Its very strong in shear and bending and wont fail in my design. It will also allow for some pre tillering before I add the horn layer to the belly.
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Most (but not all) of the reflex in horn bows is at the kasan eye, tip, and sometimes grip. Turkish bows usually don't have any reflex on the bending limb (except on the kasan eye?) unless they're flight bows? Well, war bows don't.
Massaranduba might work, but if it's an oily wood there's a chance of delamination and you might have to treat it somehow
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Nope the sals were straight before adding sinew. Any reflex in the bending limbs is due to he sinew drying. The reflex at the kasan eye is a different matter altogether. That was steam bent in to the core. Indeed when tillering these bows the most likely place for delamination is at the reflexed kasan eye.If you have too much reflex in the sals the forces acting on the gluelines are literally prising the layers apart compared to if you start with a straight limb then the forces actually press the layers together. You can make reflexed bending limbs (still minimal) as per flight bows but not for your first try!
The limb profile for your prod would be best with straight limbs through the center section and recurved tips. Stress the composite construction enough by drawing it further than wood alone/make it shorter but don't try adding crazy reflex through the bending portions.
Maple has the required charteristics for a core massa doesn't....its too dense for a start and won't accept glue as well as maple. Maple has been used for cores for an awfully long time on all sorts of bows. Any core on any bow doesn't benefit from being dense. The core has nothing to do with draw weight either it simply puts the back and belly surfaces the required distance apart for the required draw weight.
Any core you use will have to be shaped but it's best done after the horn has been glued.
Also you haven't mentioned sinew - you must use sinew for the back! Forget wood.....
Horn is a lot less stiff than most belly woods. It has less bending resistance but its elastic limit allows it to be bent 8 times further than wood. Marry this to the fact that sinew also has low stretch resistance but the ability to stretch 8 times further than wood = perfect combo.
I went to uni to study mechanical engineering and am well aware of the differences between stress/strain....it was one of the first topics.
Don't try to reinvent the wheel - use the lessons that can be learnt from the old bows made by the real masters.
Good luck with your project.
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You now say that there is in fact reflex in the bow... doesn't matter how the reflex gets into the bow, its there! Your bow has picked up reflex due to the sinew shortening when it dries (im assuming that's what happens, never used it so I don't know) which leaves the horn in tension... im putting reflex into mine using a form, also putting the belly into tension.
I'm very aware of what the core does in a bow and second moment of inertia. I make a lot of heavy draw weight tri-lam English warbows and have found that denser core timbers help to retain glued reflex.
As far as horn being less stiff than belly woods, I'd have to do a small bend test to compare them since I've never used it in bending., However, its potential for strain in bending is not what im looking for for this project. The radius of curvature along the length of my prod will be much greater than that of the limb of a turkish bow for example. I want horn for its compressive crushing strength rather than bendability.
I have found a source of sinew so I will be doubling my order or horn (if I can actually get it) and making 2 prods. One using a sinew back and maple core as you have suggested and one as an experiment with a hickory or bamboo back, JUST to see what happens with it.
I have a degree in Civil Engineering so Im very familiar with things bending and how they work, and I wanted to try something different and see what happens. We learn more through failure than success, hence my experiment.
Colin
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Well I'm not sure why you are asking for advice and then arguing with it, there is not much in common with a english warbow and a hornbow, the best approach to building bows is to be a sponge and absorb the advice given and wring out the good from the bad.
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As a guy who just makes selfbows with less than perfect staves readily available but still wants to make a bow that shoots a 10 GPP arrow over 180 FPS, I'm learning a lot from this thread. I also would like to experiment with a bamboo backed horn bellied bow. It is possible that horn alone would not be helpful without sinew on the back. But it is also possible that a special design can use horn in the belly to improve the speed of a bow. As Collin1991 suggested, a highly reflexed bow with horn belly might work, especially if the bamboo back is wide enough while the horn belly is rather narrow and thick.
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Just remember there is a fine line between innovation and reinventing the wheel...
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Your research needs to go into the french crossbows of the middle ages. They were laminated sections of horn put together like the bamboo or wood of old Yumi bows and with a thick sinew backing. These are after-all primitive crossbows and were used with devastating effect. They were Richard the Lionheart's favored weapon for his army in his conquests.