lets talk positive vs negative tiller

[Roy from Pa]

I've been thinking of making a new tillering tree bow holder for my tree. Instead of the solid 1" wide bracket I use now and place in the center of the handle. Been kicking around the idea of a 4" wide nylon strap that would float on a centered pivot point on the tree and span the 4" width of the handle area to more replicate the bow hand grip.

[Echatham]

Roy I like that idea.... been thinking along the same lines myself.... the two different cradles i have used didn't seem to be the best way.

[John Scifres]

Rusty Craine used to have a strap to hold his bow for tillering.  His contention was that it showed imbalance better by swinging.  This was before youtube so I never saw it in action but it made sense.  Not enough that I changed my setup though     I miss Rusty.

[Echatham]

wow... guess i hadn't read tillering the organic bow yet after all... i thought i had... but this is all new to me.

[Echatham]

ok, i have only read as far as this... and may yet answer my own confusion... but here he says a same limb bow will balance with the upper being stiffer.... did i read that right?

"Upon realizing this, my second generation tillering tree replaced the cradle with a radiused shoulder. It requires positioning the bow's handle on one contact point, specifically upon that contact point which most closely resembles your own handhold. Such a point would represent the dynamic fulcrum. For me, since I grip the bow by the side of the handle, that contact point is inside the thumb joint, about 5/8" below the arrow rest. By placing the bow on its dynamic fulcrum and then pulling it to full draw from the position of the middle finger on the bowstring, regardless of your finger style, you will learn what you need to know about balance and whether or not your bow achieves it. (You will better learn something of its stability, too, as rocking and twisting during the draw will reveal itself more readily with this set-up, especially from an end view.)

If you do this with a same-limb bow, you will discover that the bow only balances when the upper limb is a bit stronger than the lower limb, not weaker. How much stronger (negative tiller) depends upon the wood of the bow and the discrepancies in length between the upper and lower limb designed into the handle."

[Echatham]

you cant read something that Dean wrote without feeling smarter at the end of it.

[Roy from Pa]

I just sent Dean an email, inviting him to join in here. Hope he does:)

[canopyboy]

So, based on a conversation with Nate Steen (Sunset Hill Bows), I changed my cradle to a leather strap awhile ago.  I started with one as wide as my hand, but since it didn't pivot well, I've cut it back to about 1.25" wide.  I try to center where I think the bow is meant to be gripped.  For me, that means about 1" below the arrow shelf.  If you then pull at the correct part on the string (I use another strap of leather to approximate the pull of three fingers instead of a single hook point), you can see the bow swing as you first draw but come into balance as you get closer to full draw.  Makes sense, as you'll always be pulling on the arrow slightly above your grip center of pressure if you're shooting split.  (More in line with 3 under tillering though.)

[canopyboy]

Originally posted by Echatham:
you cant read something that Dean wrote without feeling smarter at the end of it.

Actually, I usually feel smarter before I read something he wrote...

   

(Afterwards, I'm left feeling a bit overwhelmed by what I don't know.)

[Bowjunkie]

Art, yes, the dynamic fulcrum on a symmetrical bow is round-about the top of the 4" handle, or just very slightly below it. The reason is mostly due to geometry and leverage, and it can vary slightly depending on some things, including how we tiller/time the bow, but, that is roughly where it will be. This is assuming a 3/8-1/2" high nock point and split finger grip. When I set my tree up to replicate this, as I just did again 10 minutes ago to verify, and began to draw the bow, it practically teetered on the top edge of the grip. (This is with the pull rope on the string in such a place as to replicate my middle finger’s position with the 3/8” high nock point)

Now, with the symmetrical bow braced but no pull on the string, its 'static' balance point is center of the bow/center of the handle, right? But as soon as the draw is begun, the 'dynamic' part of the balance comes into play, AND since we're pulling the string about 2" above the bow/handle center, the bow's balance makes the shift from the static to the dynamic. I can feel this as plain as day the instant I begin to draw the bow… and this is what Canopyboy sees on his tree.

Additionally, as the balance point shifts to the dynamic, almost 2" higher, the bottom limb effectively becomes graced with 4" more leverage than the top. (the bottom limb gains 2", and the top loses 2") Or as Dean put it, “…the lower limb works almost 4” farther from the dynamic fulcrum than the top limb.”

So, in the drawn symmetrical/same limb bow, the bottom limb has almost a 4" inherent, dynamic leverage advantage... AND folks frequently tiller this bow with the bottom limb stronger. So that it’s stronger AND has a 4” leverage advantage?

Countering the bottom limb’s 4” advantage and establishing synchronization is a simple matter… the top limb should be STRONGER, relative to the bottom, not weaker as is commonly proposed.

Ever notice how many guys’ bow’s top limbs are tilted forward in their full draw pics?

The path to resolve is a tillering tree setup that mimics the archer's holds on bow and string and allows the bow to show you its relative limb strength.

[Bowjunkie]

John, I miss Rusty too. Quite the character.

[Bowjunkie]

So then, by comparison… DIFFERENT length limb/asymmetrical bows...

Their ‘static’ balance/geographic center is generally positioned 3/4-1” above handle center… close to and between the bow hand and string hand fulcrums, which tends to keep the dynamic center of balance right there among them as well. In fact, since they’re all close together, unlike the symmetrical bow, it allows virtually equal leverage to each limb, and an indiscernible amount of shift to achieve dynamic balance.

Unless these are odd-shaped bows, they often reveal a neutral tiller at brace for me once they've been synchronized to full draw.

[Art B]

Hey Roy, Dean's to smart for that, LOL!

Thanks for the reply Jeff.

As Dean mentioned, there's more that one way to tiller bows. True enough, but with same-limb design, he missed the mark here. When it comes to Dean's explanation of same length limb bows he seems rather confused about it's applied positive tiller. He himself said it 'makes no sense'.

Well, I suppose it doesn't if you believe the bow's dynamic fulcrum is 2" above center or under it's arrow rest. I would draw the same conclusions about a stronger upper limb also if I believed that. Not accounting for the heel pressure of one's grip to cancel out the heavier boy on the upper limb (laughing, sorry) is his fatal flaw.

So in reality, a same limb bow's dynamic fulcrum strays very little from center. Maybe a smudge below center if anything. That's why a positive tiller or weaker upper limb works here. Limbs are always the same length, so no 4" advantage here. Longer upper limb is nothing more than the handle shifted down to accommodate  one's preferred grip.

A lot of what I see of full drawn bows is that the bow hand is not accounted for on the tillering tree.  Lower limb, right outside the lower fade takes on a greater bend when it goes to the hand. And limbs tilted forward as you describes is the result of the archer not applying the correct amount of heel pressure to the bow's handle. But then again you see all kinds of things in drawn bows Jeff. Like a full grip on a asymmetrical limb bow, or a straight wrist grip on a symmetrical limb bow.  Few bowyers understand the relationship design, proper grip per design, and their required tillers.  

So be honest here Jeff, only you, Dean, and perhaps one our two other bowyers that I've conversed with over the years have like minds on this subject. Are so few right and so many wrong?  Art B

[Echatham]

ok, i realize that Art and Bowjunkie have differing views on this... and im really hoping i can get something useful out of the debate.  i just want to make sure im understanding what you are both saying.  Jeff and dean both say you need a STRONGER upper limb on a symetrical bow... and Art says that thinking is flawed, the upper limb needs to be WEAKER.... do I have that right?  haha once i know i understand the two opinions... i can start trying to decipher the theories and physics of "why".      
and Thank you to all of you putting your thoughts out there.  It may be a little over my head yet.... but i feel like Im about to grasp some important concepts here.

[canopyboy]

Dean and Jeff's arguments make a lot of sense, I can't figure out how to refute them based purely on physics.

But I have bows with positive, negative, and neutral tiller.  The only ones that really give me a thumpin' and/or create a lot of noise are the negative ones (stronger top limb).  And I have some samples (made by myself and others) with both high wrist grips and straight handles.  Heck, I even have them in glass and wood.

The problem is that I don't like anecdotals if I can't back them up with a good physics based logic behind them.

Since I haven't completely figured it out, I start with neutral, and then slowly add a little positive tiller until the bow turns sweet.  Last bow I made was the sweetest one I've ever shot, let alone made.  Straight grip glass hill-style longbow, a little under 1/8" positive tiller.

So, I'm trying to reconcile this.  Luckily, Mr. Beam is helping me out.  (For you other engineers, we had a great Beam Theory T-shirt in college with a twist of Jim, wish I still had one.)

[Roy from Pa]

I'm playing in the bow shop right now, covered in Osage dust. Beer is cold, AC is running. Just glued on a Bocote riser on my third tri lam. Don't have to work in the morning either. I love retirement an making bows. And this is a very informative thread. I sure hope Dean surfaces.

[Echatham]

sounds like a lovely evening Roy.

[Roy from Pa]

Dean declined my invite and I understand why.

[TimBoA]

In Dean's Tillering the Organic Bow article, he mentions that he grips the bow by the side of the handle, which means the most pressure (dynamic fulcrum) is right below the arrow rest.  That is quite a bit higher than it would be for someone using heel pressure - probably a couple of inches.  Hmmm...

[Echatham]

so what it all comes down to.... if i understand this right.... is that the tree needs to hold the bow and pull the string the same way that you will.  and then the tips need to move together to full draw... synced or timed or whatever you want to call it.  correct?    so if my bow is braced and on the tree.... supported (and allowed to pivot) at the point on the handle where my bow hand will be.... and the string is pulled from where my string hand will be.    and just say i can draw a perfectly horizontal line from one nock to another.... at any point of the draw i can still draw a perfect level line from one nock to the other... and the handle does not pivot on its cradle.  would that be "perfect" tiller.... regardless of limb length?