Primitive Archer
Main Discussion Area => Bows => Topic started by: Don Case on November 24, 2013, 01:56:48 pm
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I've read in a few spots that the bottom limb should be shorter and/or stiffer. Then in other spots they have equal limbs. Would someone please clear up my confusion?
don
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Limbs are always the same length since they start at the center of the bow Don. It's where the hand/handle is placed and how much "limb reveal" if left. ;D Art
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It seems to be a matter of preference rather than necessity. There are people that make great bows using both methods. It seems the longer the bow is the more it might make sense to shorten the lower limb but that isn't set in stone either. For extreme examples look at the Japanese yumi
http://medieval2.heavengames.com/m2tw/history/miscellaneous_history_folder/japanese_weapons_folder/kyudo.jpg
or a bow like Ryan made last year
http://i327.photobucket.com/albums/k455/ryoon4690/IMG_1847.jpg
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for limbs of equal lenght people use the term positive tiller.in my interpretation this is measured when the bow is braced and placed back side down on a flat surface and the tip height measurement is compared from upper and lower limbs .the handle being center naturally places more stress on the lower limb because of hand placement and is counter acted by PT.that being said most folk will make the lower limb stiffer by +- 1/4".for example if the tip height of the upper limb is 7" then the lower limb will be 6-3/4".on the other hand some people will make the lower limb shorter by as much as 1-1/2" and have equal tip height.
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It seems to be a matter of preference rather than necessity. There are people that make great bows using both methods. It seems the longer the bow is the more it might make sense to shorten the lower limb but that isn't set in stone either. For extreme examples look at the Japanese yumi
http://medieval2.heavengames.com/m2tw/history/miscellaneous_history_folder/japanese_weapons_folder/kyudo.jpg
or a bow like Ryan made last year
http://i327.photobucket.com/albums/k455/ryoon4690/IMG_1847.jpg
Those Yumi bows are so popular outside of Japan I bet everyone has one hanging on their wall. ;D
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I have no idea. Never made any sense either way. I like the looks of even limbs so I do the positive tiller from 1/8"-1/4" positive. To me it makes more sense when you base it on how you draw. According to the bowyers bible, if you draw mediteranean(split finger) you have to do positive or shorter lower limb to get the pressure on your bow hand even(aka the limbs) but if you draw 3 under you tiller them the same, no positive or short limb, because you are drawing the center of the string, putting even stress on both limbs compared to drawing with the apex of the string angle higher than the center of the bow making it put more stress on the lower limb. Hope I didn't confuse anyone. I haven't noticed a difference unless the bow has way positive tiller. I shoot split finger and 1/4" positive compared to even tiller it hardly makes a difference. It seems to be more accurate split finger with 1/8" positive and my friend shoots 3 under and he is more accurate with even tiller. Most of this bowyer stuff is made off of what worked for some famous bowyer and likely makes almost no difference. Try and see what you tend to like more but this is what I have found.
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I just make them the same size. More on my site. Jawge
http://georgeandjoni.home.comcast.net/~georgeandjoni/handlestyles.html
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Thanks guys. When I posted this I didn't know what to Google to get an answer. I just Googled "Positive Tiller" and it looks like I've got a bit of reading to do. Starting in 2008.
Thanks
Don
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I respectfully disagree with pretty much everything said so far.
Regardless of how the bow is designed... from Yumi, to an asymmetrical English longbow, to an equal length-limbed short little flatbow, each of them should be tillered to show balanced strain on the limbs at full draw when held how the archer will hold it... and then the tiller measurements will be what they'll be.... a result... and they'll often NOT be what we'd have expected. Tillering a wooden bow, ANY bow really, to predetermined measurements at brace height and expecting it to behave a specific way at full draw and during the shot is... well naive.
Optimally-tillered bows happen less frequently with the predetermined measurement method... they are virtually assured each and every time if we tiller with limb harmony as our beacon and port.
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If you are making your limbs of different length the 1/4 inch of positive tiller is actually just limb length difference accounting for that. Your upper limb isn't actually bending more.
Place your strung bow on a grid so you can see the difference in where the tips lie and draw a line from the shorter limb to a corresponding spot on the longer limb. In fact with so small amount as 1/4 inch positive and an upper limb over an inch longer, I wouldn't be surprised if the lower limb has more actual bend.
Tim Baker's strung bamboo pole held Yumi style proves that limb length and timing are virtually meaningless . Try making one and you will find that a bow can function perfectly well with basically one working limb.
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I feel your angst!
For ages I was very skeptical about this whole lower limb stiffer, positive tiller stuff.
In general the bow is supported a tad below centre and the string pulled a tad above centre.
This imballance puts uneven stresses on the limbs. Experience has shown me that if one limb is going to go weak after a few hundred arrows, you can bet it will be the lower. I now tiller the lower limb a tad stiffer, as per convention.
On ELBs I will sometimes reverse them on the tiller half way through the build if one limb seems naturally stiffer, and make that one the lower limb.
I also take great care on the tiller to support the bow as it will be when held, and pull the string as it will be when drawn. If you tiller a bow supported and drawn from dead centre you can get a nasty shock when you shoot it for real!
Even a bow with long limbs like an ELB is effected by the slight imballance.
Look at the two pics at the bottom of post on my blog.
http://bowyersdiary.blogspot.co.uk/2012/11/caramel-and-cream.html (http://bowyersdiary.blogspot.co.uk/2012/11/caramel-and-cream.html)
Del
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I also take great care on the tiller to support the bow as it will be when held, and pull the string as it will be when drawn.
I agree completely with this technique
Art,
There are some,who make a bow with different length limbs..
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Place your strung bow on a grid so you can see the difference in where the tips lie and draw a line from the shorter limb to a corresponding spot on the longer limb. In fact with so small amount as 1/4 inch positive and an upper limb over an inch longer, I wouldn't be surprised if the lower limb has more actual bend.
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Indeed, this nicely illustrates how confusing the topic is.
My early reasoning ran like this.
The two limb have the same tip deflection.
The lower limb is slightly shorter (due to the gip bin mostly that side of centre)
Thus the lower limb must be bending at a tighter curve.
To bend a tighter curve at the same force it must be weaker than the upper limb!
At that point I realised I should stop thinking ane go by bow making experience. ;D
Del
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I make most of mine same length from center of the handle and about 1/4 stiffer[positive tiller] on the bottom limb for reason's mentioned above. DWS is somewhat right on the brace tiller not being the cure all on a wood bow but in my experience if the brace tiller is ugly and un even the full draw tiller will be also. :)
Most of the time if you keep the brace even as you go the full draw will follow along nicely. :) :)
Pappy
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I just tiller my bows for balance, could care the less which limb is what really. Im sure I have bows with upper limbs longer than lower and vice versa. I rarely measure again after the stave comes off my band saw.
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I agree with Pearl, something that has always kind of bugged me even though I know it doesn't make a lot of difference is that when we tiller the bow to how we draw it back with out fingers instead of tillering it to draw back straight where the arrow nock is. My logic is that when you let go of the string the arrow is the only thing holding the bow back, your fingers no longer matter. So I tiller drawing the bow back with my hook at the same place the arrow will nock and draw straight back from that point.
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I do the exact same thing with my hook Steve. Out to 18-19", then its all done in hand to 27". I never see a full draw of any of my bows until they are done and posted here. That's the truth.
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So if I'm following and you lay the bow out symmetrically, the arrow notch(or the top of your hand) will be about 2" above center. So then when you tiller you would hook your hook on the string 2"(approx.) above center?
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Yes sir. For me, I center the bows 4" handle and hook my string right under a properly placed nock point.
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OK! Now when the bow is finished and you're tuning it, you move the nock point up or down a bit. Is this adjusting for slight tiller differences?
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Yes, but you always want your nocking point at least slightly above the shelf or the point where the arrow rests on your hand. It gives a smoother release. I usually go anywhere from 1/8" to 1/4" above.
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I shoot three under, I generally lean tward a stiffer lower limb. :)
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Good post.....
Don C, I always had issues like you when I first started building bows. the first book I read was Dean Torges, Hunting the Osage Bow, I got confused with his book and other reads.
Thanks, Pearl and Badger for some good information.
I have learned that the tree can lie to you if you don't have the support point and hook point in the same place as your hand and nock point. I do similar to Pearl I like to floor tiller it a bit past brace, then on the tree for six or eight more inches, then I finish the tiller with a camera and me pulling it back with a arrow marked off in inches to the final draw length.
As far as limb length if I want a stiff handle bow, and the stave is clean no knots, I start with 2.5 inches either side of center for the handle, then 1 1/2" of fades. I start it out symmetrical until I get it to final tillering in the hand, and then decide what limb is best for the top or bottom by balance and how it feels in your hand as you pull it back. Also moving the shelf point up and down a bit until it feels balanced, learned that from Pappy.
I don't know what I'll do when my wife can't take the pictures for me. Use a mirror I guess. :-\
Good Luck and Happy bow building, it's a blast!
DBar