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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #1 
I just watched part 8 of the 8 part video you did with YamatarCeri?On asiatic bow building.Great series!!!The angular Egyption bow that inverted after shooting,how low was that bow braced?I ask because I'm making a hickory with a horn belly and sinew back that will be narrow about 1 and 1/4 inch wide and have about 4 to 5 inches of reflex pulling 55# at 28".The string is just off of the tips of bow at  about a 5 and 1/2" brace to the belly of the handle.I know this is not a bow building site but thought you might be able to elaborate on it.I met you back in the 80s' sometime at the New Ulm camp up in Minnesota.Got your series of books too.They've been a very good reference for me.Braintanning hides etc.
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prariewolf

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Registered: 11/28/06
Posts: 162
Reply with quote  #2 
Oops! Thought that I had posted this last night - but not. OK tho because another thought came to me.

The angular Egyption bow that inverted after shooting,how low was that bow braced?
I can't recall. That was a LONG time back.
 
I think that the length of your bow would make the most difference.
Generally I have strung my Shorter bows - 40 inches (+-) at the height of my closed fist - fingers - maybe 4 inches. The longer bows Are generally strung at the height of the clenched fist plus the raised thumb - approx. 6 inches. This is for self (wood) bows.
On the composite bows - we have strung them a bit higher. 
The self bow brace height is based on the 2:1 ratio between arrow draw length being 1/2 of the bows length as this is approx the optimum ration to get the very best results from the equation - ballistic co-efficiency in bullets.
That ratio is not the same in composite bows as the compression (the limiting factor of maybe 4-6 percentage where the compression ration of wood is a dismal 1%) (sinew maybe 10-12% more tension).
So --- a coupla things to bear in mind. Since the composite bow can draw further (much further in theory) than can the self bow you don't need have the string travel further (keeping in contact with the arrow for more efficiency) as (1) there is so much more extra energy already stored in the bow thru reflex and (2) using longer than 2:1 draw ratio you would be drawing a much longer arrow than 2:1.
NOW ---- you say that you draw 55# @ 28". If your bow is 56" then you'd be drawing 2:1. For a composite bow to function as it should - ie., give the best ballistic co-efficiency - it would need to draw at a much higher rate than that. The Monguls made and used these bows so successfully because it allowed them to use a short bow - 40 or so inches - and yet have a full draw length of 30 or so inches. As an example, if you made a self bow and a composite bow that had same reflex, draw length and poundage, the self bow would be somewhat, if only a little, more efficient because horn and sinew weigh more than wood and this weight would slow the action.
 
You do need tho to keep in mind that there is always a chance of the string slipping to the sides of the base of the “ears” if there is no bridge on which the string to rest - more of an issue the narrower the ears. This is, in fact, what I recall as being the issue with the Egyptian bow you refer to. So, if the string were to not stop at the base of the ear (siyah) and traveled to the side of it, there would be a good chance of the bow inverting - and yes, a higher brace height would help to correct this.
 
You did not give the length of the bow and width info if the ears/bridge and that would be critical in any close to definitive answer.
 
Ponder this and get back to me. If I run out of knowledge I'll try to refer you on.
 
John
 
Speaking of New Ulm - Geri and I are at the moment at the Mayo Clinic in Rochester, MN for a follow up with surgeons after removal of a brain tumor four months ago - and yes, she's so far doing well.
 
 
 

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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #3 
That's great!!! your Geri is doing good John.My bow is 60"t/t 58 and 7/8" n/n.Finished her out to 57 to 58 pounds at 28".I took a hickory stave and made a 25# bow then added 3/32" horn on belly and gave it three courses of sinew on the back.Gave it about 4 inches of recurve the last 10"in front of tips.It had 7 and 3/8" reflex before tillering and am left with 4 and 1/2" after tillering.Just low enough I can string it with the push pull method.I'm bracing it about 7" to back of handle so about 5 and 1/2" to belly of handle.Could be higher I guess.Shoots good and flat at 30 yards.The string does occasionally slap the limbs after release.No inversion whatsoever.Par for the course getting worried for nothing.LOL.Yes there is a give and take in construction of bows.It's hard to beat a simple plain old self bow all things taken into account.Still glad I touched base with you.I see we are both a little more gray as time has gone on.You engineers just love these bows don't ya?......LOL.
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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #4 
I get what you mean though that in order for a composite bow to shoot faster than a wood bow the composite material would have to be put to work more[ of which it is capable] with a longer draw length to counteract the extra weight that composite material carries.This bow ended up being 1 and 3/8ths" wide yet at the fades tapering to 1 and 3/16th" at the end of the working limb.Instead of of side tillering I did a little belly tillering on the horn.Taking 1/8th the amount of mass weight off as opposed to side tillering.It came in at 18.75 ounces of mass weight which I thought was just about right for a 57 pound bow that is 60" long.Thanks for the info John.
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dixieangler

Registered: 06/11/09
Posts: 133
Reply with quote  #5 
Quote:
Originally Posted by "prariewolf"
Geri and I are at the moment at the Mayo Clinic in Rochester, MN for a follow up with surgeons after removal of a brain tumor four months ago - and yes, she's so far doing well.


Good news. Thoughts and prayers to you and Geri.

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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #6 
John I lived 45 years of my life in northwest Iowa and Rochester was THE place to go to for solutions for something like Geri and you are going through.The world seems to be a different place when scary things like this happen.I'm extremely happy things are on the mend.You guys are blessed.
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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #7 
Hello John.....I've been shooting this bow in here before finish work.It's mass weight is 18.75 ounces.I suppose you might know this fella Steve Gardner from the Bowyers Bible series.He wrote a chapter on tillering a bow keeping a watchful eye on mass weight as the tillering process goes along to final draw weight.For performance reasons.This bow pulls 57 to 58 pounds at a 28" draw.It's 60"t/t and 58 and3/4"n/n.It rests with 4.5" of reflex.Of that just after shooting and unbraced it shows 3.5" reflex.That 3.5" is what I figure the arrow is getting in stored energy.According to my calculations and Steve Gardners mass principle this bow should have a mass weight of 20.25.I did do a lot of side tillering on this one with a little belly or horn tillering.It's shooting a 577 grain arrow from 173 to 177 fps.These fps figures and testing on bows are very controversial to say the least and I'm not the biggest fan really.I just wanted a bow consisting of a higher percentage of composite material for durability reasons and possbly performance if the design and tillering was right and done correctly.I hope to God now that it holds up for me.It has shown absolutely no signs or sounds of danger.Time will tell.
While watching you and Jeffery Smith on you tube I saw him give his final course of sinew on that bow as a long complete full stretch along the entire limb.I used beef backstrap sinew of which it is about two and one half feet long on this bow as my final course.The first two courses were deer leg sinew.Reverse bracing this bow as it cured.
I hope you can appreciate this because a little birdie told me one time you and Tim Baker got together showing off your favorite bows and Tim had to go home eating crow......LOL.Is this true?

Take care
Ed.

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prariewolf

Moderator
Registered: 11/28/06
Posts: 162
Reply with quote  #8 

Ed - you're getting way ahead of me in tech specifics. 

I rarely tiller from the width as you then have to remove so much to make a little difference (50/50). As far as being concerned about the longevity of your composite, I would worry little as long as you're secure in the knowledge that you built it correctly, being more than a little careful in gluing the surfaces, keeping them clean and allowing sufficient drying time.  

Looking at the specs that you have given me, this bow should never be under enough stress to fail. According to my figuring you are not pulling quite 2:1. The composites that I have worked with actually have had no tillering. Normally I have used 1/3rd thickness each of horn, sinew and wood. The wood is only a gluing surface for the horn and sinew which do all of the work, the wood lying in the zero stress neutral plane zone. While the sinew will stress well over 10% the horn is the limiting factor stressing maybe 4-5%. Your bow is now stressing right at what a well tillered self bow should, close to 1%. So - this stressing of 1% when it should/could be four to five times more is not stressing your product.

When I build a composite following the 1/3 rule it is a bow approximately 40 inches to draw an arrow 30 or more inches. The only tillering I do is from the belly as I'm always concerned about cutting thru the sinew threads on the back - and the tillering is ONLY to get the two limbs to bend equally to each other - NOT to get the limb to bend evenly overall. If I (you) were to tiller to get the limbs to bend evenly overall to transfer the stress equally as with a piece of wood stressing 1%, you will not get the efficiency out of the limb(s) that you should. When building as described (1/3rds) and only tillering to get the two limbs to be equal, the stress, bending of the limb(s) when drawn, is only in the 4-5 inches on either side of the grip (the remainder of the limb is static). This then allows the stretch of the sinew and the compression of the horn to better “snap” back to equilibrium at its maximum effort giving MUCH MORE ballistic coefficiency (SP? - maybe not a word?) to the bow.

 

With Geri, we were fortunate to get to Mayo as quick we we did. They are full of competent and caring people and we happened to draw one of top, if not the top, surgeon and this came out as best it could. MRI Tuesday last showed no recurring of a recurring tumor so we're good for another six months until the next checkup.

 

Yes, Tim Baker & I did happen to have with us what was for each of us our latest and best creation (bow) at Rabbit Stick about 1989 or so. I can't recall his but mine was a 48" or so Osage Orange, maybe 1.5-2" wide, static siyahs of 5-6 inches built kinda as an Eastern composite without horn. I was testing the compression of what for me was the hardest wood available, very old and well cured Osage Orange. I can't recall the draw length but it was greater than 2:1. We shot side by side and mine shot further the first two arrows. On the third round I suggested that he should angle a bit higher, closer to 38-40°, and he then beat me. He called it for me but it was more a draw and likely if we kept at it and he adjusted his angle better it may have turned out differently. Anyhow, it was GREAT FUN. Somewhere I have a photo of the two of us at that moment and If I could have laid my hands on it I would have attempted to share it with you.

 

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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #9 

I see about the tillering of Asian composite bows.Just get the two limbs to match bendng like each other,but only on a small portion of the limb.Yes I can see why the 1/3 to 1/3 to 1/3 can take so much more stress.I suppose [and I'm just estimating here]this bow of mine would be 1/6 to 1/6 to 2/3.Now going with the engineers' knowledge[which does make sense to me....LOL] that 10% of the surface does 50% of the work and 20% of the surface does about 80% of the work and 30% of the surface does 95% of the work it all makes sense.Especially laying that last layer of sinew down as one long continuous course.Anyway thanks for the verification of knowledge from someone in the know.

Take care
Ed.


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Beadman

Registered: 08/26/12
Posts: 7
Reply with quote  #10 
John would you happen to know or remember how long you left the snake skin on your sinewed bow dry or how long Jeff left the birch bark dry on his Asian bow before bracing and shooting it?I plan on putting a snake skin on with titebond 3[an enhanced white wood glue].I'll leave the bow set in an enviornment of 40% to 45% humidity at about 85 degrees F.Probably put a fan on it too to help it dry.I'm assuming here that the application of the snake skin will not reduce reflex of the bow if given time to dry and not stressed any.Thanks again for the insight.

Take care

Ed.

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prariewolf

Moderator
Registered: 11/28/06
Posts: 162
Reply with quote  #11 
I have no experience with this and cannot recall what Jeff did here.
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