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Elasticity versus poundage

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willie:
Ed, you have raised a very interesting question, and as I have not yet built a horn and sinew wood core bow, I cannot offer any specific recommendations based on experience.

Having played around with backings and given some thought to the nature of composite constructions, I would like to bring to the discussion a few questions that might be pertinent to arriving at an answer to your question. Of course, as always, the devil is in the details, and as these considerations may not be complete,  any additional design considerations would be welcomed.

The 1/3 - 1/3 - 1/3 layup seems like a good point of departure for comparing successive bows of similar designs, but is does raise the question of whether the sinew and horn need to be applied in equal amounts of thickness. Why not 1/3 - 2/5 -1/5 ?, or whatever ratios the back and belly are best capable of?  Does the sinew and horn have the same stiffness and elasticity?, there by only adding thickness and poundage to the bow without shifting the strains in the core?

Presuming that your hickory is both lighter in mass and stiffer than either the horn or the sinew, why would the core for the composite you describe, be best served by tillering to twenty pounds? Is that how thin it needed to be for your design to flex the full range from reflexed to full draw? Why would you not want it to be as thick/strong as possible, as long as it was capable of bending the full range without taking undue set?



 

mikekeswick:
Willie the 1/3rds rule isn't set in stone but a good starting point.
If you go thinner with the horn the bow will acquire more string follow. If you go thicker then the bow will be more resilient and keep its pretillered profile better.
If you go too thin with the core then the bow will be less easy to stabilise. Thicker and you run the risk of it breaking.
Sinew thicker than 2/3mm isn't necessary. Thinner = broken bow.
Sinew/horn have similar resistances to bending.
The core and horn have to be exactly dimensioned before sinewing or else you will have 'built in' weak/stiff spots that cannot be fixed. Ed's way of pretillering the core is a good idea as it will eliminate this. However you want to be very careful and not pull it far at all.

BowEd:
willie.....Those are all good questions and Mike is all together right.I won't be afraid to pull this bow to 29" and will more then likely tiller it to that also.A few things I paid attention to constructing these bows is from 3 books really.First of course Adam Karpowiczes book.The other 2 volume 1 and 4 of the TBB series books.Tim Baker and Steve Gardners findings are fully engaged here.The degree of  % of depth the surface works on a bow.Degree of work certain sections of the limb length doing work.Just deducting common denominator facts and applying them.Attention to mass weight.Inspiration can come from many places.That seems to be the key.I will leave that up to you.
Nothing wrong with different degrees of thickness of components.Mike explained the up and down side of them.Going 25/50/25 sinew/core/horn will work fine too.No specific well rounded numbers either because through tillering horn or sinew thickness can change to a small degree also.The thing is to use composites on shorter bows with extreme reflex to get the most out of the composites.The balance that horn and sinew have to each other is unique.Otherwise like said the mass weight will negate the efforts if going for performance if applied the full length of longer bows.Really no reason for that in my mind.
More detailed measuring/weighing is required.Lately I've been writing info on paper for future referral.I will be able to tell you exactly how much each component mass weighs when shooting the bow in.What starting mass weights are.The whole nine yards.Like I said earlier more detailed but to me worth it because of the strain these bows will be under.Getting the most you dare from the components within reason.This goes for all materials really.Even self bows.
Horn bows are just fascinating bows to me.Equaling and out shooting their modern counter parts is what tickles me,and just plain works of art in my mind.After all it is the Primitive Archer site right?I hope you sometime try your hand at some.I've got a lot of unchartered waters with them to discover myself.Making self and sinewed bows before hand is very helpful.It's not for everybody that's for sure.Never a dull moment though making these if the inspiration is there.I hope this helps you.

willie:
thanks for sharing your experience, Mike

working knowledge trumps theory in my book, after all primitives did not have to know "why" to make it work. ;)

BowEd:
Well willie seems the asians were at the fore front of a lot of it.Other cultures too just from necessity.Lacking father to son apprenticing written info is the only thing a person can do to learn.Lucky it was documented and shared.A person's gotta start somewhere and aquiring knowledge of the whys and why nots is essential too even before beginning.

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