Positive tiller..why is it required? How does it vary with shooting style?

[George Tsoukalas]

DCM, we keep bringing up the term fulcrum as regards to the bow which implies it's a lever yet, as bowyers we do everything to prevent our bows from becoming levers i.e. we do not want our bows rocking back and forth as we draw them. I am beginning  to conceptualize the bow as a spring. I haven't gone much beyond that. Jawge

[NOMADIC PIRATE]

In chapter " Who's on first what's a second' Torges advocates to make simmetrical (equal llimbs ) bows with negative tiller, who's making them like that ? 

[DCM]

George,

It is both a spring and a lever I believe.  Fulcrum is just a convenient term.  It doesn't really matter as long was we communicate effectively the underlying concepts.

I was really disappointed that you did not accept my last invitation to discussion.  I hope my style, my choice of language does not put you off, that it's not intimidating.  It's not that I am so certain in what I believe that I argue forcefully, if I do, only that if yer gonna argue something there's no point doing a half-arse job of it.  Did you read any of that Tapley stuff, the part about nock travel being the natural consequence of short/long spring theory?

[DCM]

"...to make simmetrical (equal llimbs ) bows with negative tiller..."

I think the most generous evaluation of that article would be to assume he simply used it as a literary device.  In a sense he is right, in order to balance the load between the two limbs and prevent fatigue, the shorter limb would need to bend less to reduce the strain on it and bring it into parity with the longer lower limb.

A less generous view would be to observe that even though it would tend to balance the load on the limbs, it would at the same time introduce an inescapable tuning problem.  Specifically, given what we know, or should know, or could know about nock travel, making the upper limb stiffer would tend to push the arrow into the arrow pass shelf, rather than away from it at the end of the power stroke.  On the other hand, Dean doesn't exactly advocate the arrow pass above center bow.  Rather, he advocates arrow pass at center and observes correctly that the arrow pass above center design only exaggerates the asymentry, given the desire to have the arrow leave the bow from perpendicular, or if any disparity nock slightly above arrow pass versus slightly below.  Given this constraint, you want the nock travel to be generally above the perpendicular, the natural effect of weaker, longer spring being the upper lmib, versus the opposite.

Although I think I have it right, since this stuff is horribly complex and confusing for me I sure wish more folks would try to understand it and if not explain it to me, at least challenge my understanding, if I'm wrong.

[Marc St Louis]

David
If you take a bow with the dimensional center in the palm of your hand and measure the top and bottom limb then they will both have the same length, or they should.  That, to me, is a bow with symetrical limbs.  A bow with asymetrical limbs will have the lower limb, usually, shorter than the top limb.  If your bows are different then you are making them differently than I am.

[DCM]

Marc,

I think every bow I make is different from the last, and probably different than yours in some measure of this aspect.  And it's easy to have a really long inconsequential exchange about the meaning of terms, how one measures stuff, whether a limb includes the non bending portion above or below dimensional center.  

An easier way to have the discussion, the discussion of "Positive tiller..why is it required? How does it vary with shooting style?" is in my view by approaching the quesition from the point of view of the arrow during the power stroke.  That's why I refer to string segments, spring rates of the upper and lower limbs, essentially parroting the work published by Tapley, modelled by Kooi as I understand it.

http://www.goarchers.org.uk/mechanics/

Also, don't think because I advocate a particular point of view that I necessarily have made some kind of value judgment on one variation or preference over another.  To put it another way, your bows are excellent as far as I can tell, as are Eric's, or Dean's or JD's or whoever and I know for a fact they all vary considerably in a variety of aspects.

What you've described I would consider a bow with a shorter upper limb, one where the arrow pass is 1" to 1 1/2" above dimensional center and one where the fulcrum of the bow hand, in your terms "the palm of your hand" is at center.  Based upon my understanding such a design would require a bit more positive tiller to compensate for or mitigate the tendancy of nock travel in the verticle plane during the power stroke.

But sometimes I can be incredibly dense and stubborn, so if you are game and I've misunderstood or misspoken please keep after me.

[Marc St Louis]

David
I disagree, of course.  From what I can see it's simply a matter of perspective.  You seem to see the bow from an arrows point of view.  I look at the bow from the bows point of view.  To me if both limbs are dimensionally equal then they both can take the same strain, not to say they need to or do.  This to me makes a bow happy and it can fulfill its function, storing energy for the arrow.  The arrow can take care of itself  and if it is well made will do so.  A limb that is dimensionally shorter has less wood for bending purposes, less wood means it's ability to store energy is less.  That is the limb that needs to have more positive tiller because it cannot bend as much or it will suffer the consequences...the wood will be more strained so more set. 

The reality is that a bow will tell you when it is balanced.  All you have to do is feel it as you draw and that can be with some positive tiller or not. Sometimes it will actually be with some negative tiller but that is rare

[Red Dwarf]

OK I am trying to understand things here; excuse me if I go over a few points.

Positive tiller is where the top limb is slightly weaker than the bottom...correct?

One of my bows is a takedown, both limbs are the same length (it has symmetrical limbs). The deepest part of the grip, where the centre of resistance provided by the bow hand is, is in the dimensional centre of the bow. The arrow pass is approximately 1 inch above dimensional centre.
This is a symmetrically limbed bow...correct?

I shoot 3 under. My nocking point is 1/2" above the shelf and I nock my arrow below the nocking point. When I draw the bow I figure that the majority of pressure on my drawing hand is on my middle finger, the centre of which is about 1 1/2" below the nock which means that I am pulling from the centre of the string.
Why does the bow need positive tiller???

Red Dwarf

[George Tsoukalas]

David, don't want you to be  disappointed. Both sides get entrenched, nothing is solved, terms get thrashed around, the Red Sox are in the play offs and have a chance to win their division. No your style of discussion doesn't put me off. I mean I was raised in a Greek family. You want forceful...Just don't have much more to add to the discussion except this - if the bow is both a spring and a lever then you must feel it is  a "compound" machine. Rather ironic. I am willing to discuss the bow as a lever or a spring. I haven't really thought about the spring concept much until our last foray on this topic.  I think knowing what the bow is - is pivotal for this discussion. Jawge

[Rich Saffold]

Red,
Usually you want an 1/8th to 1/4" more distance from the belly to the string on the upper limb. I shoot with two fingers, and like less than an 1/8 difference on my personal bows. When I shoot "normal" or Mediterranean style there is no difference in how the bow feels.. Why because the arrow just is along for the ride.

And if the bow is shooting properly, How you shoot it doesn't matter enough to feel. I shoot a couple of my bows where the arrow and how I grip the bow is within 1/2" and it feels no different than when I shoot the bow with the arrow 1.5" above center.  These factors don't matter whether the tiller is even, or 1/4" positive. The percentage of how far the arrow sits above center is so low it really doesn't matter, especially for all the debating that goes on about it..

The reality is the chronograph shows no advantage to any set-ups mentioned here, so how the bow feels in your hand, and arrow flight matters most.

Rich-even length limbs, symmetry at full draw works for me

[Red Dwarf]

Please excuse me for being slow, I am pretty new to all of this but....If I grip the bow in the centre and pull the string from the centre why do I need positive tiller?

Red Dwarf

[DCM]

Because you can't apply pressure to the bow at a point perfectly perpendicular to the corresponding place where you apply pressure to the string.... because you can't shoot and arrow thru the center of your hand.  Rather one must position the string hand above the bow hand, in effect shortening the upper limb.  A short limb stacks ahead of a longer one, so we introduce a little extra weight to the lower from the outset so that at full draw they come into parity. 

Sorry guys, I know this topic deserve more attention than I've shown but bow season opens in a few minutes and I been bizzer 'n a cat covering scat.

[George Tsoukalas]

DCM, I am disappointed that you do not want to discuss this issue. Seems you have blown us off for hunting season. You can't find time for us? I guess that's the way it goes. Jawge

[George Tsoukalas]

Just kidding! Season started here in NH 9/15. I haven't seen a deer yet. Hope you get one. Hope I do too. Jawge

[Red Dwarf]

Surely, with the pressure point of my bow hand in the centre of the bow and my drawing hand pulling from the centre of the string my drawing hand is not above my bow hand ...I'm confused??

Red Dwarf