Primitive Archer
Main Discussion Area => Bows => Topic started by: arachnid on January 10, 2015, 12:12:01 pm
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Hi Guys.
When tillering a symetricl bow, how do I know how much stiffer the bottom limb should be?
I've read that it needs to be slightly stiffer but how much is slightly? How do I mesure such a thing?
And, is there a difference between a straight limb bow and a reflex/deflex desigh (like a 3 pc takedown)?
I'll be graetfull for any info on the subject.
Thanks
Dor
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I never measure for positive tiller. On most selfbows you can only measure accurately at full draw, IMO. I just look at it and see if the bottom limb is slightly stiffer.
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+1 Pat, most of mine are apparent at brace but those oddballs absolutely necessitate measuring/looking at full draw.
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How much is "slightly"?
How do I eyeball it? Does it need to bend evenly but less the upper? (Meaning the tip is a bit higher, when looking on the bow on the tillering tree)?
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The gap between mid-limb and string should be just sliiiiiiiiiiiightly greater in the upper limb (take any character into account!)
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I measure the greatest gap between belly and string on each limb at brace. Ideally, that place should be the same distance from center on each limb but I find it varies a little here and there. I shoot for 1/8 positive tiller but seldom get it. 1/4 ish. How does is shoot is a much better guide than some quirky measurement, though, IMO. Just use measurement as a guide.
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We are not talking about rocket science or brain surgery here. It is "primitive" archery. Slightly is a little less than too much but not as much as not enough. ;)
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Easy to do with a lam or board bow with straight tips.hold the back against a door frame and measure from frame to tip.rotate 180 and measure again. Oddly enough the set will also equal the pos tiller when unbraced if it's balanced.hard to do with recurve because they are rarely identical and will pull out a bit when worked.same for staves from. What I've seen so far.
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1/4" is fine. Have someone snap a digi pic or check in a mirror. A window at night works too. Jawge
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We are not talking about rocket science or brain surgery here. It is "primitive" archery. Slightly is a little less than too much but not as much as not enough. ;)
I about spit out my drink, great answer Pat
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Arachnid, unfortunately "slightly " is the right answer. I'm sure every individual bow has a sweet spot, but it's going to vary with the archer and his grip, and the style of bow. A shorty might look and feel very lopsided with 1/4" difference, while a long, long, longbow might want more.
Look at the Yumi design, and look at the archers hand. You can get away with a lot, obviously, if you shoot it right.
What I keep in mind primarily is the strain on the wood. If the lower limb is a tad shorter, it will act stiffer. I want to strain it that tiny bit less then, so that it doesn't take MORE set than the top limb.
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I guess thats where the "art" comes in to play... knowing that sweet spot.
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Yeah, and I don't always find it, but that is why people go with rules of thumb.
How about this. Imagine you had a bow that bent perfectly symetrically, with the hand's pressure point exactly in the middle, and the drawing hand directly behind that. Now, the arrow has to pass above the hand, so it is an inch, plus, above the middle point. This brings the string hand up a bit, too, so now the pressure points on handle and string don't line up, and the lower limb acts slightly weaker (string applies more leverage).
So, if you cut just enough off the lower limb to make the STRING even again, narrow and re-nock the lower tip, you'll be in the neighborhood.
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I guess I've never paid too much attention to measuring it. I try and make the bottom limb the slightly stiffer limb. I usually set out with the intention that a particular limb will be top and one bottom, but it does'nt always work out that way for one reason or another and I have to shift gears and swap top and bottom.
Thats also one of the reasons why I don't like cut in shelves. If I find the need for a shelf for someone to shoot off of I glue one on with built up leather. I have also found that if the bottom limb starts out stiffer, after its shot in pretty well it tends to balance out due to the fact there is more strain on the bottom limb. Danny
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I try to make the bottom limb slightly stiffer,, just enough so I can see it at full draw,,
if the arrow is not flying right or the arrow is hitting my hand a bit,, I will make it stiffer until the bow shoots smooth,, that being said,, it the bow is shooting very smooth with good arrow flight,, I figure the tiller is good and I dont look at it any more :)
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In vol. 1 of the bowyers bible. John strunks chapter 'The Yew Longbow'
He explains how to accurately measure positive tiller@brace. Via diagram.
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I'm always saying this but again I will say that drawing the profile of the bow onto something BEFORE ever bending it will tell you all this stuff.
Forget tillering trees for the last few inches of draw - they almost always put different strain on the limbs than drawing by hand.
So to check if the amount of positive tiller is correct.
1 - Check the set precisely against your profile on your piece of paper/whatever (I use the wall).
2 - Make any corrections you think are necessary. Get the tiller where you want it to be.
3 - Draw the bow 20 -30 times. More is better when fine tuning.
4 - Unstring it hen immediately check the bow against your profile.
5 - The set will tell you if everything is as it should be. No guessing! Set is the cold, hard truth with no subjectiveness.
There isn't a 'fits all' numerical answer to your question but the set WILL tell you the answer. :)
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1/8 to 1/4 on most of mine @ brace, some say it don't matter and I guess it really don't but I have found over the years if the brace tiller is close the rest will generally follow suite, if it is ugly and uneven the bow will usually be also, :) not always with a tricky/knotty or snaky stave but most of the time on a fairly clean normal one. :) JMO. ;) :) :)
Pappy
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It good to keep them close as you go, trying to pick up just a 1/4" on some bows will cost a lot of weight. I have been caught off guard more than once like this. Other times it may not drop much poundage. I have been working on this hickory bow the last few days and it keeps going back to negative when I shoot some arrows through it. I think I finally have it now but it has dropped about 10#. Which in this case is ok anyway.
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First of all, thank you all for answering.
I'll ask it another way- what will happen if I tiller the bow evenly? The bottom limb is stressed more, but then what?
Does the trouble of getting into positive tiller (and a chance to screw up the tiller) realy worth it?
As I recall, most if the bows published here appere to have an even tiller.
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It's about where. The fulcrum is being your hand places more stress on the bottom limb and over time it will surcome to set throwing off the tiller and shortening the bow life.imho.
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The big reason you want to have positive tiller is so the bow will stay balanced in the hand throughout the draw. You cannot do that properly if you tiller the whole thing on the tree. Once you get it within 5 " or so of your full draw, draw it back and feel if it rocks in your hand. you will know if one limb is bending too far without even looking.
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Slightly is a lttle less than too much. :) Jawge
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...but a little more than not enough, George! ;)
I usually tiller my bows even on the tree but leave the bottom limb slightly(there it is again) stiffer during the last few inches of tiller. I go by tip movement at full draw.
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I go by tip movement at full draw.
Pat, can you explain that?
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If both limbs are bending evenly and together the lower limb tip should come down just slightly less than the upper tip. I eyeball this.
The back drop of my tiller tree is concrete block so that's the grid I use.
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Well, that sounds simple enough (the simplest method I've heard about thus far)... hope I don't mess it up. Thanks Pat.
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it is not all about the way it looks, it has to shoot,,, on l longer bows it does not seem to have as much effect, but if the tiller is off on a short bow,, it will be harder to get good arrow flight,,
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I've been shooting a 66" white oak backed ipe flatbow for the past 6 months, that turned out to have a positive tiller and it shoots pretty good for all I can tell.
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If I set the arrow rest so the arrow is in the center of the bow, then basicly when I draw the bow (even with split finger)
I draw it in the center of the sting, there for, eliminating the need for positive tiller.
Correct?
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Nope.
Don't forget about the bow hand? It isn't holding the bow at the center. It's holding well below center.