Tiller. Split vs 3 under.

[Bill B.]

Alex C. Started an excellent thread to explain the geometry of tiller and now I have more questions.

3 under.
 It’s been my understanding that the bow should be tillered even. In my mind this makes sense because the fulcrum (string fingers) are now closer to center evening the levers (string to limb tips). But I’ve noticed the 3under shooters set a high nocking point which increases the lever length to the bottom limb again. This seams counter productive to me. What am I missing here? Trying to help a friend but I have no experience with 3 under. Other than shortening the point on distance, are there any advantages to 3 under?

Split finger.
I tiller using the mass principle and the back profile of the limbs. About an inch or 2 before hitting my draw length I start checking limb timing in my hands. With a relaxed bow hand I can feel the stronger limb tipping towards me. A few scrapes will usually get the bow to sit straight in my hand to full draw. This produces 1/8” - 3/16” positive tiller. Set ends up around 1.25” - 1.5”.
Bows are well mannered and of average speed. I’d like to reduce the set some and hopefully pick up a little performance. Any and all input is appreciated.

Sorry for being long winded. Posting is rare for me so I thought I’d put both questions out here.

[Del the cat]

My view is that on the tiller, the bow should be supported where the hand will support it (and allowed to rock). The string should be pulled from where the fingers will draw it. This will look odd as the draw starts, because the bow will tilt, but that is exactly what happens in the hand.
IMO it is a mistake to support dead centre and draw from dead centre as it doesn't accurately simulate real usage.
Del

[Jim Davis]

Seems to me that tillering should be from where the arrow sits on the string. I've never done that, but when we loose the string, the limbs immediately pull against the arrow nock....I'm just sayin'...

[Selfbowman]

Jim I’m not sure I agree. The weight of the arrow resisting the limbs to come to rest is minimal. The release of the limbs is more critical. By not tweaking t he limbs at release there is less vibration. Now that being said a double knock might be of assistance. I have never shot flight with a double knock and sometimes no knock at all. Interesting topic though.

[Badger]

 I go along with Jim Davis on this one, the second you release the string the bow forgets where you were holding it and starts responding to the arrow. People forget that an arrow weighing only slightly more than 1 ounce will way more than 1# under acceleration.

[Selfbowman]

Steve where do you put the scale hook when tillering?

[Badger]

even with the bottom of the shelf

[Alex C]

I've been thinking about the same thing lately.  The big difference is the location of force applied to the string by the fingers at full draw and by the arrow on release.  For three-under shooters, that point moves ~1", whereas it really doesn't move at all for split shooters. 

No matter the method used to get to a final tiller for three-under, we pretty much have to choose between it being 'perfect' for the draw or the release (or maybe tiller so that the center of force is somewhere in between).  I'd imagine that a bow tillered so both limbs apply the same force to the arrow would be a better performer, though that means the bottom limb is more stressed by fingers at full draw.

Shooting split seems to solve it though! Maybe I should try shooting split again... it's been years and I hated it....

[Selfbowman]

Guys I haven’t got this all figured out by any means.but when shooting flight I use two fingers split. So should I make my top limb 1” longer and shoot middle of the bow??

[Selfbowman]

Question does the hand on the bow torque the bow when held?  Does the bow want to bow Down at top limb and if so why.

[Jim Davis]

Arvin, for your flight shooting, these things probably matter. For hunting or 3D, as long as everything is the same shot to shot, we can put the arrow where we want it.

[Bill B.]

Thank you for all the replies!
I’ll be rounding the bow support on my tiller and moving the scale to the aero position from the middle finger. Hopefully this will eliminate some of the unneeded stress during the Tiller process.

Alex
My friend tried my suggestion to lower his knocking point by quarter of an inch. He says the bowl is now quiet with excellent arrow flight. It’s no longer broken so he’s all done fixing it. I still don’t understand the physics/geometry of “why” this worked. If you have any insight on this, I would love to hear about it.

[Selfbowman]

Jim I agree with you totally. But I have broken lots of records tillering from center of bow then razing the shelf 1-1/4” and the string knock a 1/4” higher from there. Knocking underneath.And again i think a wood bow settles in to the way an archer shoots the bow to a degree.A glass bow will not take set to accommodate for any archers personnel shooting style. So I’m not sure this makes a Hugh difference. You just need the arrow to come out of the bow clean. Yes  I’m sure there are lots of folks disagree with my thinking but I have had success with this method.

[Alex C]

Alex
My friend tried my suggestion to lower his knocking point by quarter of an inch. He says the bowl is now quiet with excellent arrow flight. It’s no longer broken so he’s all done fixing it. I still don’t understand the physics/geometry of “why” this worked. If you have any insight on this, I would love to hear about it.

Bill, that makes sense to me from a geometry perspective - to be honest, I have FAR less experience than most folks on here when it comes to bow building, I just have a knack for physics.  So most of my thoughts on this are theoretical and not backed up by experience. 

The nock point just may not have been ideal for a few reasons, many of which are solely dependent on the arrow and not the bow.  But ignoring arrow dynamics, lowering the nock point to solve the problem would make me think his top limb was probably storing/expending more force than the bottom, so tuning would be difficult.  With the lower nock point, that takes strain off the top limb and places more on the bottom, potentially allowing both tips to arrive at brace height more simultaneously and with more equal force. Again, just from a geometry perspective.

It could also just be the angle made by the limb tip, arrow pass, and nock point was just too acute at the top and to big at the bottom.  No bow/arrow combo is going to like extremes for those angles.

[Alex C]

Guys I haven’t got this all figured out by any means.but when shooting flight I use two fingers split. So should I make my top limb 1” longer and shoot middle of the bow??

Like I said earlier, take my insight with a grain of salt because I have no real-world data to back any of this up (yet), I'm just doing some math. 

But I can absolutely see why shooting split finger would be better for flight shooting because there is little-to-no energy lost in the transfer of force from the fingers to the arrow on release - they are pretty much the same point on the string.  I'd imagine shooting from the geometric middle of the bow would mean equal length limbs could be much closer to equal tiller for maximum efficiency.  Raising the nock or shelf would mean you'd want a slightly longer top limb - the more you raise them, the longer the top needs to be.  Having a stiffer bottom limb would have the same effect as having a longer top limb from a geometry perspective.