Primitive Archer
Main Discussion Area => Bows => Topic started by: Steve Cover on February 05, 2010, 05:54:46 am
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Maybe i missed in my search, but I didn't find that answer I was looking for.
Question: Are bows tillered to have the equal strength on both limbs.
The reason I ask is that most of the bows I've owned, It seems that the lower limb was slightly stronger than the upper.
The reason the knock point is not at 90 degrees??
Anyway, can anyone shed some light on my query, or am I just mistaken?
Thanks,
Steve
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the way i understand it, the lower limb and upper limb should bend the same, except if the upper limb is longer, in which case it should bend more...english longbow style
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I think most people tiller the lower limb a bit stronger, its called positive tiller.
You should consider investing inThe Bowyers Bible Vol 1-4 its not a huge investment for the amount o0f knowledge that they contain :)
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On same length lombs I usually tiller them about 1/4 to 3/8 heaver on the bottom limb.
If the top is longer by an inch or so I tiller them even. :)
Pappy
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Thanks guys,
I was starting to think I was seeing things.
Also, thanks for tip on the Bowyer's Bible, I'll check that out.
Steve
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Steve, I suppose the reason most nocks are 45 degrees is because it is closer to the angle of the string when the bow is drawn; although on some flat bow stlyes like the Modoc and pyramid the nocks are often cut in pretty much perpendicular (90 degrees).
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My limbs are the same length (at least they used to be; getting older now.). I tiller the bottom limb stiffer.The nock point is a little higher than 90 deg. That depends on limb tiller and the split fingered draw. Jawge
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"Question: Are bows tillered to have the equal strength on both limbs."
Here's some of my thoughts on the subject:
Yes, but how you achieve that is by the way you grip your bow. For example, you're building a bow and know nothing about positive tiller. But you have enough common sense to know that both limbs should feel even strain at full draw. Now, how you grip your bow during the tillering/shooting-in process will determine the amount of positive tiller (or lack there of) you will end up with. Someone who uses a low wrist grip vs a high wrist applies greater heel pressure to their handle causing a need for a stiffer lower limb to achieve even strain at full draw. So a bow designed for a low wrist grip will show a greater positive tiller than the person using a higher wrist design.
A note: some, for their on reasons, like to favor placing more pressure on the upper limb requiring that limb be stiffer. Again, how one grips their bow will determine ones needs. So if you see a bow tillered negative, you can't automatically assume that it's out of tiller.
"The reason the knock point is not at 90 degrees??"
Taking into account the arrow's dia. and the distant that the string nock pushes the arrow nock down (because of string angle) your string nock will most likely be between 3/8 to 1/2" above square on average. ART
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"Question: Are bows tillered to have the equal strength on both limbs."
Here's some of my thoughts on the subject:
Yes, but how you achieve that is by the way you grip your bow. For example, you're building a bow and know nothing about positive tiller. But you have enough common sense to know that both limbs should feel even strain at full draw. Now, how you grip your bow during the tillering/shooting-in process will determine the amount of positive tiller (or lack there of) you will end up with. Someone who uses a low wrist grip vs a high wrist applies greater heel pressure to their handle causing a need for a stiffer lower limb to achieve even strain at full draw. So a bow designed for a low wrist grip will show a greater positive tiller than the person using a higher wrist design.
A note: some, for their on reasons, like to favor placing more pressure on the upper limb requiring that limb be stiffer. Again, how one grips their bow will determine ones needs. So if you see a bow tillered negative, you can't automatically assume that it's out of tiller.
"The reason the knock point is not at 90 degrees??"
Taking into account the arrow's dia. and the distant that the string nock pushes the arrow nock down (because of string angle) your string nock will most likely be between 3/8 to 1/2" above square on average. ART
Thanks, That is good information.
I've always used a high wrist grip... (I only own recurves)
(http://i160.photobucket.com/albums/t175/SteveCover/Shooting/Archery/SilverArrowRange1965001.jpg)
In the past, when setting a knock point on a new bow, would shoot fletchless arrows into my target from close range.
I would mark the string at the point the arrow entered the target straight on, and place my knock point there.
Depending on the fistimal, the knock point was always located to place the arrow a variable distance North on 90 degrees.
That helped fuel my interest in positive tiller.
This very old picture (1962) shows the lower limb with less bend than the upper.... I always wondered if it was just an illusion...
I appreciate your detailed answer. It has laid to rest several of my questions.
Steve
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It sounds, daft, but I think there must be some confusion over the terms strong, weak, long and short.
The 'working portion' of lower limb is often the same length or shorter than the upper limb.
However the nocking point is often above centre of the string and handle is all below the arrow pass.
This gives some strange geometry, so the terms 'weaker' or 'stronger' aren't necessarilly correct as the two limbs aren't under the same conditions.
The way I see it is the lower limb generally has to bend through a slightly tighter arc, and the whole issue is best resolved on the tiller tree.
If you mount it on the tiller as close as possible to how you will actually hold and draw the bow, and tiller it so that as you draw the string back and forth the handle remains stable and doesn't rock back and forth, then I figure it's gotta be right.
I think it's a matter of doing what works rather than trying to analyse it.... a shed load of physics probably wouldn't help tiller a real wood bow...and ain't that just why we like it?
Del
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Hey Del, if we're dealing with a shorter lower limb then that means that the handle has been shifted down the bow to accommodate for a lighter grip. Perhaps "off set handle" would be a less confusing term than long or short.
The tillering tree can't account for the hand's heel pressure that's needed to engage the lower limb to compensate for the bracing effect created by the drawing hand being above the bow hand. Only tillering on the tree for the 3-finger under draw would be the closest thing in terms of narrowing the gap between the center of the bow and string. ART
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Hey Del, if we're dealing with a shorter lower limb then that means that the handle has been shifted down the bow to accommodate for a lighter grip. Perhaps "off set handle" would be a less confusing term than long or short.
The tillering tree can't account for the hand's heel pressure that's needed to engage the lower limb to compensate for the bracing effect created by the drawing hand being above the bow hand. Only tillering on the tree for the 3-finger under draw would be the closest thing in terms of narrowing the gap between the center of the bow and string. ART
Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately.
Mine has a radiused block with a thin rubber covering, I place the bow on it at the point where my hand pressure will be, The string is drawn back by a two pronged hook which approximates the with of my fingers under string pressure, it is very noticeable how much differnce there is between that and supporting the bow dead centre and pulling the string back dead centre.
Maybe you can't simulate a very heavilly contoured grip like on a recurve, but even so, the force should pretty much come through a single point (or the geometric centre of a pressure area).
If the hand is having to provide forces to stop one limb coming back more or less than the other, I'd say it is tillered wrongly, as surely the bow hand should be relatively 'soft' (relaxed)?
It's a good discussion point, and one of the probs is expressing what one actually means!
All just my opinion of course...I'm not trying to be dogmatic (or catmatic?).
Del
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"Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately. "
Can't argue you point Del....................cause I use to do things very similar to you. So I know exactly what you're saying. But through the knowledge and experience I gained over the years I since moved on with a better understanding of how things work. Again, sorry I can't argue you view...................ART
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"Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately. "
Can't argue you point Del....................cause I use to do things very similar to you. So I know exactly what you're saying. But through the knowledge and experience I gained over the years I since moved on with a better understanding of how things work. Again, sorry I can't argue you view...................ART
I'm interested in what other people think feels right.
Are you saying you like to feel the lower limb pulling/pivoting the bow into the heel of your hand?
I can see that might feel 'right', I've just not tried it myself... (yet ;D)
PS. I've only just spotted your original post which makes it clear what you mean...sorry.
Del
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:-X :-X :-X :-X :-X :-X
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"The reason the knock point is not at 90 degrees??"
Taking into account the arrow's dia. and the distant that the string nock pushes the arrow nock down (because of string angle) your string nock will most likely be between 3/8 to 1/2" above square on average. ART
Art, I would appreciate it if you could expand/explain this a little more. I have always felt that adjusting the nocking point for the shooter was crucial. I think positive or negative tiller can be compensated for, at least partially by adjusting the nocking point. I don't have a complete grasp on it, so your input is very interesting to me.
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I'm with Del on the tiller-setup-can-compensate question, but I think setting your pulley off center so it pulls through the off-90 nocking point is what makes it work. Simply setting the handle in the right spot won't do it by itself if the bow isn't drawn the way it will be drawn by hand.
Nobody's mentioned the high nocking point in terms of fletching clearance... If the point isn't high, the fletching and nock bounce off the shelf and cause poor arrow flight. If the nocking point is tuned so the back end of the arrow just clears, the flight is self-correcting. A vertical-plane archer's paradox to go with the regular around-the-handle paradox.
If I'm wrong correct me! I'm here to learn.
Garett
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i think the reason we do nock grooves at 45 degrees is this:
more or less, a bow is made where the overall length is twice the draw length plus the handle. That is, each limb handles half the stress. 25" draw means approximately 54 to 56" overall length. each limb, then, equals the draw length. Pretend it is a triangle, with the 3 sides being the string, the arrow, and an imaginary straight line running from handle to tip. Two of the "sides" are equal: in this case, say, 25". It's a right triangle, because the string is pulled perpendicular to the handle. Any right triangle with the base and height being equal (1:1 ratio) gives a resulting 45 degree angle at both other points of the triangle. I know this is a terrible explanation. But draw yourself a picture.
In practice, 45 degrees for the nock groove is NOT usually exact, but it is near enough.
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Justin, the one thing I've learned over the years is that a good release is way more important that having an exact string nock position. If the bow is in any way out of tiller then timing is compremised and so is the nocking position. That's why it's so critical to lay an arrow pass out and then grip the bow accordingly for best limb timing. In my opinion, you want the arrow to leave the string as close to 90 degrees as possible.
If you will take an arrow and nock it on a bow string and then cant (mimicking the arrow at full draw) it about 45 degrees you will notice the arrow nock fits tight against the front of the string nock and has a gap of around 1/16" between the back of the string and arrow nock. When the arrow is released, it does not stay directly under the string nock, but rather below the string nock that 1/16" I mentioned earlier. I read about this close to 40 yrs ago and ever since then I have included this in my calculations for nock setup. Plus the dia. of the shaft of course.
Zenmonkeyman, if I read you correct, you're referring to a similar effect of archer's paradox or the bending of the arrow upon release where the arrow first bends inwards against the arrows pass. Yes, I think you will get a similar but less effect of over the shelf paradox (porpoising) just from the arrow itself (with the string nock being in the correct position). This could bump the arrow up slightly upon release and create a need for a higher string nock then one would think.
But to reiterate, a good release cures many ills. ART
ART
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Thanks Art,
I've been archery since 1951.
Your explanation of why the nock point is raised above the arrow at 90 degree to the string, is the first one I've seen that is clear enough for me to visualize.
Thanks for you excellent answer. I haddent considered the possibility of a vertical Archer's Paradox like action of the arrow.
PS no slight is intended to the others who have courteously answered too.
Your responses have greatly helped my understanding, with perspectives I hadn't considered...... (I'm not all that bright..)
Steve
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You guys have got me totally confused now. If one limb is shorter than the other when you tiller it, one will be heavier, but they should both bend equally to form a "D" is that right.
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Robbsbass, this is my take on things.
Even strain on your limbs should be felt at full draw. So the amount of hand/heel pressure used determines how much extra weight/stiffness will be needed for the lower limb to achieve equal limb balance at full draw. Only reason to have an off set handle/shorter lower limb is if you use a medium to straight wrist grip. Here less hand/heel pressure is used creating a lesser need for positive tiller/stiffer lower limb. The proper amount of positive tiller will "create itself" if limbs feel even strain at full draw, using the proper arrow pass layout for one's desired grip.
Knowing this, we can recommend, say for example, 1/4" positive tiller for same length limbs w/low wrist grip, 3/16" positive tiller for a 1" shorter lower limb w/medium grip, around 1/8" positive tiller for a 1 1/2-2" shorter lower limb w/high/straight wrist grip. Or an even tiller for someone that shoots three-finger under where the hand placement on the handle and the finger placement on the string is pretty much center of the bow.
Again, just my opinion here folks.................ART
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Makes good sense Art. Steve
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Thanks Badger................ART
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Thanks for clearing this up for me.
Robb