Question for horn bellied bow builders

[colin1991]

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

[james parker]

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

[colin1991]

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

[Aaron H]

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...

[mikekeswick]

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.

[loon]

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..

[colin1991]

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

[loon]

Hmm, maybe a nylon or polyester cable back could work...

[bubby]

Go to a butcher shop and see if you can get the leg tendons thats where you get sinew if you can't hunt

[DC]

Kangaroo sinew would probably be primo See if you can find a hunter. That is if it's legal to hunt them.

[colin1991]

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

[loon]

not sure if hickory makes a good core or not (if it absorbs animal glue well?)

[colin1991]

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

[loon]

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.

[mikekeswick]

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.