Ozbow

Hi all,

have been working on the designs for a small project and found that timber as a belly for the particular bow just won't cut it...

So I thought maybe I'd try horn as its far stronger in compression than wood, but keep to a timber back and core.

has anyone else ever tried this particular thing before?

Colin

Hi Colin. Mis you are thinking of Asiatic style bows, they use slabs of horn on the belly of wide flat limbs.

http://www.manchuarchery.org/content/bow-making

Don't know how a timber back would fair up against the very stiff horn belly though. They put a very heavy sinew backing on the bows in the link above.

Cheers... Rod

Reading between the lines, this means you're having Ironbark fail in compression with a Hickory backing? Wow! I've been getting Hickory & White Oak backings splinter with Celery Top Pine & White Cypress belly's on short working limbs - I can't imagine what you must be doing to get compression failures with timber backings!

I think if you use horn in long, unpre-loaded limbs it can be too heavy & sluggish, a bit like using Osage in an ELB. I've never used horn as a belly material but I've thought about it a bit. I've considered maybe an acrylic or plastic in a horsebow, replacing the horn....?

Thanks Rod, I have been looking at this style of bow for a bit of research on the topic but the design is vastly different to what I want to make. Ideally I would make the bow using horn and sinew to be historically accurate, however, sinew (real stuff) seems to be fairly hard to obtain unless you can hunt it yourself.

Yet to test Ironbark Neil, but spotty went to crap and its pretty hard stuff. The bow in question was 40" ntn and failed pulling 120lb @ 16 inches... I don't want to go to far into exactly what I'm making tho. Just think very short and very heavy!

Osage is a fantastic ELB wood mate!! you can push it way shorter than 2.5 x draw length... Mate of mine in Canada has an osage warbow that's 72"ntn and he draws it to 32... 115lbs...

In my opinion, timber fails in compression because of high stress in conjunction with high strain... and this particular design calls for both of those things at once so I need to find a material that can cope... looking at horn, I think it will do the trick, though ive been told it wont work at all already. We shall see!!

Plan (most likely) is to glue up a back and core in some slight reflex and then pre tiller down to a 3" or so brace to ensure the limbs are even. Then I will glue the horn to the belly and heat shape it to the reflexed curve where necessary. Adding an even thickness layer should just mean an increase in draw weight and I can add as many layers as necessary to get the weight I need.

Colin

hunterguy1991 wrote:..... I don't want to go to far into exactly what I'm making tho. Just think very short and very heavy!......

Some form of Arbalest?

Daryl.

Possibly

What's your opinion on my plan Daryl?

Sounds like you need to use steel

hunterguy1991 wrote:What's your opinion on my plan Daryl?

Destination unknown, think variations on leaf springs.

Daryl.

Have already thought of steel lads!! Only issue is the tempering of such a long piece evenly.to make it spring steel.

What length is the prod going to be?

40" ntn... 16" is full draw, that's 2.5x draw length for the prod.

There was a fella on paleoplanet undertaking a similar endeavor, as I recall he used yew for his limb at a similar length and pulling around the same poundage, ill have a dig around for it and send you the link once I find it

As I said, I'd ideally like to do a horn and sinew version but cant get the sinew for it, so im experimenting and improvising

I will be making a steel one one day tho!

Adding an even layer of horn in the hopes it will evenly raise the draw force might lead you down a frustrating path, unless the limb is already a consistent thickness.

If the horn is truly a consistent thickness, and is added to a tapered belly/stave, then it will be proportionately thicker out at the tips, the limb will no longer taper in proportion, and the tips will be stiffer.

The effective working strain of horn is something close to 4%. Really good woods are rarely over 1%. What can we do about this without sinew? If I was engaging on this thought experiment, I would glue the horn onto a middle lam in almost semi-circular shape, then once cured pull those two lams almost straight before putting the backing on. This will place the belly material under much more strain than the back at a given deflection.

The again, are there any deer farms near you? I've spoken to a few and found them to be rather sympathetic to my cause, especially when they hear what I do and make.

Best of luck on your endeavours!

Hey Hunterguy,

I'm from Adelaide, the worlds most barren desert in regard to bowmaking materials! But even here I've spied big bags of kangaroo sinew for 50-odd bucks at a particular pet feed/fodder store......would have thought you'd be sure to have such businesses up in your neck of the woods? I don't know if they'd freight, but the business down here is named 'Olivers' at Morphettville, South Australia. Plenty of sinew here, just no bloody wood to stick it to!!:):)

Thanks for the thoughts on the prod Dave.

I will need to do a few calcs to see how the composite affects the stiffness and deflection. Even if the taper is close but the tips get a bit stiff I can still tiller the horn as normal to get them moving a bit more.

Interesting thoughts on the glue up tho! I will experiment and see how I go.

Cam has been kind enough to get me some sinew so I will be making up 2 prods, one experiment with a timber back and one of sinew like a legit one.

G'day Sabinus. I cant say that I have seen sinew in pet shops... plenty of pigs ears tho! Happy to send you a stick down to play with if you'd like?

Colin

Deer Sinew

Try your local traditional chinese medicine supplier.

eg
http://www.btrt.com.au/en/product/deer-sinew

Hey Colin, Was as Olivers on the weekend - maybe Adelaide is 'The Sinew Capital' of Australia! Goat tendons $50 1kg bag, Roo tendons $50 1kg bag, and single 12"long (beef?) sinew pieces $3ea. And yes they also have an extensive selection of pigs ears-heaven!!!

Thanks mate!! Will definitely keep you in mind when I need more!! and I will definitely be needing more down the track