Author Topic: Elasticity versus poundage  (Read 1029 times)

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Offline Beadman

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Re: Elasticity
« Reply #15 on: March 19, 2017, 08:41:02 am »
gfugal.....I actually fibbed a little in my opening paragraph.This bow is 2" shorter than the one before.Soooo I figured it to be 5#'s stronger then too at 28".Thus probably equalizing itself out in draw weight to the previous one at the same thickness.
Your right though there is no reason why a good compression strong wood could'nt be used here.Personally I'd go with osage.I know more bout that wood then ipe.I've heard you've got to almost have a perfect piece of ipe..no pins etc. to hold up.Osage is much more versatile or forgiving to me.
You got to stand for something or you'll fall for anything.
Ed

Offline Beadman

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Re: Elasticity
« Reply #16 on: March 19, 2017, 08:54:20 am »
Here's a pic of tip alignment.I adjusted this while tillering it to brace first so I did'nt need to fuss with that while tillering but still may need a tweak or so we'll see.
« Last Edit: April 03, 2017, 05:29:09 pm by Beadman »
You got to stand for something or you'll fall for anything.
Ed

Offline Beadman

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Re: Elasticity
« Reply #17 on: March 19, 2017, 09:07:11 am »
I'll get a string on her gfugal.....lol.
You got to stand for something or you'll fall for anything.
Ed

Offline Pat B

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Re: Elasticity
« Reply #18 on: March 19, 2017, 09:35:53 am »
That's a sharp looking bow Ed. I have one in my future but....
 Do you think the extra physical weight of the thicker composite components will negate any of the potential benefits.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Beadman

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Re: Elasticity
« Reply #19 on: March 19, 2017, 09:49:49 am »
Nope.If made right what your questioning is pretty much a myth.
« Last Edit: March 19, 2017, 05:49:35 pm by Beadman »
You got to stand for something or you'll fall for anything.
Ed

Offline mikekeswick

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Re: Elasticity versus poundage
« Reply #20 on: March 20, 2017, 12:39:20 am »
Interesting to hear others thoughts on the subject but all that determines poundage is the overall thickness. The varying ratios of the three materials would change things very little. However it would be a bad idea to go too thin on the wood as that is what gives the bow its shape and lateral rigidity. The ideal is to have the total thickness evenly divided by the three materials to make best use of their different properties.

Offline joachimM

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Re: Elasticity versus poundage
« Reply #21 on: March 20, 2017, 02:09:18 am »
Interesting to hear others thoughts on the subject but all that determines poundage is the overall thickness. The varying ratios of the three materials would change things very little. However it would be a bad idea to go too thin on the wood as that is what gives the bow its shape and lateral rigidity. The ideal is to have the total thickness evenly divided by the three materials to make best use of their different properties.

My thoughts too. poundage doesn't come from the core, but from the distance the working portions (sinew back and horn belly) are from the neutral plane, hence thickness. If the core is too thick (strain>1.5% - the backing does hold down splinters so it tolerates higher strain than unbacked bows), it will break just like a normal bow, no matter how much sinew and horn you have. If it's too thin, it will tend to twist when put under high strain.
You could add some sinew to increase thickness and hence poundage, but in the end you might end up with a sluggish bow as the first 2 layers of sinew are close to being dead but heavy mass.

It's good to experiment and question existing designs. However, most of the time there's a good reason for a particular design.

Tillering is easy. Problems arise when a bowyer thinks he's right and the wood is wrong.

Offline Stick Bender

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Re: Elasticity versus poundage
« Reply #22 on: March 20, 2017, 02:41:12 am »
Thanks for the answer Mike I couldn't wrap my brain around the ratio vs strength but it makes sense for draw weight I was confusing weight vs performance which would be another whole  thread but a interesting one thanks for posting learning a lot here Ed !  (=)
If you fear failure you will never Try !

Offline Beadman

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Re: Elasticity versus poundage
« Reply #23 on: March 20, 2017, 08:12:49 am »
Thanks fellas.Great comments.Overall thickness/staying within the design....that all makes sense for ease of final tillering.Too much horn makes it more unstable or a bit wonky I call it.Can only imagine at the moment what it's like making an all horn/horn sinew bow.This current bow is close to the 1/3,1/3,1/3 ratio yet of components with the core being a shade more ratio wise.Overall thickness is the same as previous bow but like said 2" shorter overall.Overall mass comparing to the last one is the same too but like said again can depend a lot on what component having the most mass for poundage for performance.Horn versus core mostly.Keeping the ratio within reason is good.Crowning the sinew will help with performance.Tapering components before sinewing to put the most material where it is needed and bend the way it should is a bit like self bow making to refer to.I guess I just wanted to stir the pot a little on this thread.Maybe others considering making a horn bow will learn a little.Seems the only way to learn making these bows right is Adam Karpowiczes book mostly.Most people who make these type bows are accomplished bow makers referring themselves to that book and a lot of people don't have it.
They are fun to make but are not quite like the ease of roughing out a stave to a bow and making a fat 3/8" line along the side for a taper that's for sure like said again but really don't require any more sophisticated type tools or equipment,but some are just different that's all.Making calculated measurements of each component etc.Making these makes a person think quite abit more about different forces going on etc. too.In the end getting a deeper understanding of bow making IMO.
« Last Edit: March 20, 2017, 10:20:05 am by Beadman »
You got to stand for something or you'll fall for anything.
Ed

Offline Beadman

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Re: Elasticity versus poundage
« Reply #24 on: March 20, 2017, 10:34:21 am »
joachimM....The koreans at times use rather thin layers of sinew.Total of 2mm at most.Mostly on bamboo though?Reflexed from the handle etc.
I've done some extensive testing with the previous bow I made and it does shoot comparitively right up there with other horn bows listed in Adams' testing list.Using FF string though of 2gpp.Curious to see if any at all difference there is with this one.
I should apologize to Pat B probably but not sure if what he stated was meant about the ratios of components or the lengths of bows getting sinew depleteing performance.In the past it was discussed extensively that longer bows up to 64" did'nt benefit from sinewing.I've proven here if put where it works it does enhance performance.
« Last Edit: March 20, 2017, 10:38:19 am by Beadman »
You got to stand for something or you'll fall for anything.
Ed

Offline willie

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Re: Elasticity versus poundage
« Reply #25 on: March 20, 2017, 09:11:54 pm »
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?



 

Offline mikekeswick

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Re: Elasticity versus poundage
« Reply #26 on: March 21, 2017, 01:13:20 am »
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.


Offline Beadman

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Re: Elasticity versus poundage
« Reply #27 on: March 21, 2017, 07:43:25 am »
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.


You got to stand for something or you'll fall for anything.
Ed

Offline willie

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Re: Elasticity versus poundage
« Reply #28 on: March 21, 2017, 08:24:12 am »
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. ;)

Offline Beadman

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Re: Elasticity versus poundage
« Reply #29 on: March 21, 2017, 08:35:57 am »
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.
You got to stand for something or you'll fall for anything.
Ed