Primitive Archer
Main Discussion Area => Bows => Topic started by: willie on October 12, 2017, 04:11:47 pm
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this is a pic from Physics of Bows and Arrows Paul E. Klopsteg
I would say the tillering job looks good, but what limb shape is it best for?
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The lower limb looks a smidge stiff to me. It looks like the bow is tilting downward and the string angle isn't quite the same. But that's going off of an even unbraced profile. I'm leaning more towards a pyramid profile. For a parallel limb I'd want a tiny bit more stiff at the inner quarter to third.
Kyle
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(-P
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The tiller is acceptable(good assesment by Kyle), but its hard to make a judgement not being able to see the same bow, at brace, unbraced, or the design of the limb.
Is this bow one of Klopsteg's own bows made by his hand? I'm skeptical of all the authors /physicists that championed a scientific way of designing a bow as being the best way to make bows. The bows that I have made following their recommendations turn out pretty average. I would have done a better job doing it all by eye. Wooden bowmaking is more art than science due to natural variation in wood.
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Easy :)
Pyramid
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Hamish
the pic is from a magazine article about various aspects of the bow and arrow. No special claims were made for the bow, as the pic is shown in an explanation of stance and aiming.
I just got curious because no other pics were available, and I like the bow
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In this instance, it doesn't really matter what the unbraced or braced profile looks like. The bottom limb is too strong, the limbs aren't dynamically balanced. Notice how the bottom isn't flexing near as much as the top. Since it isn't moving as far as the top limb, the stronger bottom limb is pulling the string hand and tail end of the arrow downward, and is noticeably below perpendicular to the shelf. I bet that arrow porpoised on its way to the target. Look at the picture sideways. It's more apparent that way.
If the limbs were balanced, the arrow would come straight back, effectively maintaining its height relationship with the shelf, and in all probability, would be perpendicular or sightly above perpendicular. I highly doubt if he nocked that arrow an inch below the shelf to begin with. I also wouldn't be surprised if that bow's tiller changed.... bottom limb got weaker with use.
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Well he is known too be one of the best at his time. So I would say good. Looks like a field archer to me. Sting walker also possible . I don't really know but my guess. :-) Arvin
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How much does shooting split finger, anchoring below jawbone affect the full draw profile?
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I highly doubt if he nocked that arrow an inch below the shelf to begin with
you have a good observation, DWS. The arrow seems to be nocked at what would be level with the shelf, (deduced from a few measurements from the pic) I suppose that I would have to look at it a bit harder if it was on my tillering tree.
In the same article he does mention a pyramid bow designed by hickman with this force draw curve
https://www.google.com/patents/US2100317
wonder how it shot?
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Bottom limb looks a bit stiff mid limb, other than that looks fine to me. Brad ;D ;D ;D ;D (-P
Pappy
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Tiller is very good. Lower limb is shorter giving the appearance of being too stiff. Jawge
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Bow is also being aimed slightly upwards adding to the illusion
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Looks like positive tiller from here...I also think the photographer was kneeling...Noticed arrow length, nothing showing shaft point in picture...Looking at anchor and wondering if he's a gap shooter or instinctive...Looks like a tournament shot from 60 yds, the "American round" gap shooting...
Don
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Relative limb balance has been at the forefront of my bow building for a long time, I almost wish it hadn't been because it drives me nuts sometimes... but yeah, I notice stuff :o
Arvin, I was taught by some of the 'best of their time' to take none of this for granted, question everything, everyone, and that includes fairly and objectively critiquing the work of others, but especially those who offer instruction, or have good reputations. Who better, and what better way to improve our own understanding and craftsmanship?
Willie, the arrow MAY have been nocked level with the shelf(we'll never know), but the arrow won't STAY level with the shelf as the bow is drawn if the limbs aren't balanced with one another and the archer's holds.
Jawge, I measured them as best I could. The limbs appear to be the exact same length.
Stickinthemud, I don't think there's an illusion that something's wrong, more likely that the bow being aimed slightly upwards helps hide the fact that there's an imbalance.
Donald, positive tiller is a judgment/presumption made at brace height, that is 'supposed' to result in a dynamically balanced bow at full draw, is it not?
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Here's the same picture with the handle/shelf area straight up and down. I have to imagine that, with the bow held equally straight up and down at brace, before the draw had begun, the arrow would have been level with the ground or slightly elevated at the nock end.
The nock end of the arrow came down during the draw because the bottom limb didn't flex as much as the top.
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And here's how the picture would have looked had he kept the arrow level with the ground during the draw. Notice the relationship of the arrow to the shelf/handle area and how the bow is tilted. The stronger lower limb isn't flexing enough and is pulling the bow into the heel of the hand, while drawing the nock of the arrow down... as it's being drawn back.
We CAN make a bow that's balanced while more heel pressure is applied, if that's how we wish to hold it, but it would/should still reveal balance at full draw... i.e. arrow straight back from the shelf/handle, bow not tipping in the hand one way or the other.
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And this is approximately how it would look on my tillering tree.... but not for long ;)
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Nice set of pictures; I am happy to stand corrected, if that were my bow I know I would be trying to bring that bottom limb around a touch more, but probably only after I posted a 'help me please' photo to PA! ;)
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Has a nice positive tiller. Looks nice to me
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Good point, DWS, but I like the bottom limb slightly stiffer. Jawge
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Interesting responses, I had hoped that more would have been willing to suggest the back shape that corresponds to the bends on this bow, as "what does the back look like" is often asked when a bow is presented for tiller evaluation. I have to admit that the curves look pleasingly smooth, even if they are two different "unbalanced" curves. All three aspects are important, even when prioritized differently by different bowyers.
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More or less even bend along the limbs shows that for even strain the thickness must be the same/very little taper. A pyramid bow.
The slightly stronger lower limb thing is simply because we don't shoot through the center of our hands :) There is no way to have exactly even strength limbs and a human shoot the bow (and it stay 'in tiller'). We have pressure point/s on the handle and the arrow goes above this/these hence asking the lower limb to do a bit more.
I've messed about with dynamic balance and adjusted my tiller tree to show if the limbs are balanced on the way to full draw by being able to see if the string deviates from a 'straight back' path and it is worth doing....but the problem with it is trying to replicate the way the grip is held/supported by the hand.
Anybody interested in this method can search 'limb timing' thread by 'bowjunkie' over on tradgang.
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if the bow shoots well, the appearance in any way is secondary,, (SH)
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The top limb bends quite nicely. The lower limb bends too much in the outer limb and not enough in the inner limb= lack of symmetry. The bow would probably have some hand-shock
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Mike, Bowjunkie is me :)
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could it be possible the bottom limb had a bit of reflex,, giving it the appearance of not bending enough,,,
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Brad, very good inquisitive question. But no. If, for instance, the bottom limb has 3" of reflex and the top is even with the handle, when dynamic balance is achieved at full draw, the top limb will likely be drawn farther behind the handle than the bottom, but the arrow will come straight back relative to the shelf/handle, without causing the bow to tip in the hand.
Folks often ask... "One tip is ahead of the other... should I level the tips or the handle in the tree?" Definitely level the handle. That's how you intend to hold it, right?
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By the way, Mike, the cradle doesn't have to precisely replicate the bow hand's hold. We can get close enough by most standards if the cradle spans the width of the grip or otherwise holds it in place, and then we adjust the limbs so the string hand fulcrum comes straight down. But we can locate or move, by adjusting limb strength, the exact dynamic pivot point at full draw by putting the bow on the tillering tree, placing something under the handle at the supposed point of dynamic balance to allow the bow to tip one way or the other, then draw it from our string hand's fulcrum point. This reveals us. We can still adjust it so the bottom limb is a little strong if we like, but I bet the vast majority of folks will be surprised at what they find .
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DWS are your bows free to rock in the cradle or are they fixed in some way?
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DC, I have both.
I don't clamp it down. My cradle is shaped so that it supports the handle at its ends only, this keeps it from tipping unless the limbs are far from being balanced. I also have inserts of various shapes that drop in which allow it to pivot.
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How far apart are the supports? I'm liking the sound of this.
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In my mind I don't think you can tell every thing about the tiller by one full draw shot , if the bow shot to point of aim & was whisper quit ,zero hand shock & minimal set then I would say regardless of the full draw pic the bow would have great tiller , but those are unknowns I think a unbraced shot is as important as the full draw, plus it's not known where he knocked the arrow to start , the limbs seem to be bending smoothly so the bow would probably live a long life !
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DC, 4" Same width as the handle.
Stick Bender, you're right, there are unknowns and I'm making a few assumptions. I'd love to have seen that bow unbraced before tillering, and unbraced again after 1000+ shots. I'd bet my best osage stave that if it took any set, the bottom limb took more set than the top. I'm just commenting on what appears to be going on in that one pic... assuming, odds are, it started straight unbraced, with the arrow nocked as is normally done.
Limbs can each 'bend smoothly' in their own right, but be FAR from balanced.
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This might help
(https://imgur.com/a/PMSaU)
The actual link
https://imgur.com/a/PMSaU