Author Topic: How does tiller affect performance?  (Read 6812 times)

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Offline Badger

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How does tiller affect performance?
« on: August 24, 2016, 03:16:53 pm »
   I think this is a good topic and I expect somewhat theoretical as I can't give prove of any of my own theories. That being said I feel the best tiller shape would be one that allowed the outer limbs to start moving first during the draw and allow the bend to progress inward during the drawing process until the last few inches where the near handle wood starts to bend. Most of us including myself are usually tillering for a desired shape so to some degree we ignore the progression of the bend. An Elliptical tiller will usually facilitate this pretty well. Circular tillers I feel are the biggest cause of handshock. Having only the outer limbs bending as the string returns to brace during the shot lowers the momentum of the limbs and gives the arrow a lot better control over the limb mass. The arrow needs to slow the tips down to extract the energy or else it will be lost to vibration.

Offline bradsmith2010

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Re: How does tiller affect performance?
« Reply #1 on: August 24, 2016, 03:40:41 pm »
hmmm let me think a minute,, :)  nice topic

Offline Danzn Bar

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Re: How does tiller affect performance?
« Reply #2 on: August 24, 2016, 04:56:36 pm »
I'm still trying to get my head around the definition of the word tiller ???
DBar
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Offline Dances with squirrels

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Re: How does tiller affect performance?
« Reply #3 on: August 24, 2016, 05:09:35 pm »
I don't think there is a "best tiller shape"... just like there isn't a best fly rod taper or action for all fly casting.

I don't tiller for a desired shape, per se. That's a mistake I see some, especially less experienced folks make. They try to tiller all of their bows to the 'desired shape' in their mind's eye, regardless of the vagaries of the stave or blank's profile. Some even try to bring pronounced d/r  or reflexed bows to the same full drawn shape as a straight standing bow, and assume all those limbs are working the same because they look the same at full draw.... nope.

I like your thoughts on bend progression, and that's how I tiller most of mine, shape notwithstanding.

Online sleek

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Re: How does tiller affect performance?
« Reply #4 on: August 24, 2016, 05:20:15 pm »
I look at this in terms of cars.

You have torque and horsepower. Your outter limbs are your horse power and inner your torque. Proof? All tje strain of a bow is focused in the handle. It is the highest concentration of potential energy. As you move outwards you get more kenetic energy simply because you have more movement. Hp is a measure of that.

So, on take off, you want high torque, and at top end is where your want all your hp.  A bit redundant  but making my point.

So you release your arrow, first thing you want to move is your inner limbs, letting all its torque into the arrow, and as tje arrow speeds up you want that energy to be coming from close to the tips. As the arrow releases the string you should have nothing moving except the tips.  If the entire limb is still moving, a consequence of the inner limbs still having energy, the hand shock will be bad.

As common sense would follow the first thing to move on the draw would be the last on the release. Tips should move first on draw.
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Offline SLIMBOB

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Re: How does tiller affect performance?
« Reply #5 on: August 24, 2016, 06:23:36 pm »
Great topic. and one I have spent some time ruminating over.  I like the idea Sleek put forward.  Good analogy.  As to whether getting the bend to run from outboard - inward...is that the ideal?  I ask the question because I am unsure.  That is to some degree is how I tiller most of mine, without giving it much thought during the process.  I have been threatening to build an Elmer Wilcox Duoflex for years now.  I have toyed with it on several staves and cant get the balance anywhere near right.  Stability issues yadda yadda, so I've yet to get close.  If you look at the FD curves on them as reported, they are pretty amazing for a wood bow.  They are built quite to the opposite.  Thick inner limbs bend first before the working recurves open up at the end of the draw.  I believe Marc built one if not more some years back.
I think it was actually Russ Willcox. 
« Last Edit: August 24, 2016, 06:46:37 pm by SLIMBOB »
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Offline red hill

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Re: How does tiller affect performance?
« Reply #6 on: August 24, 2016, 06:40:32 pm »
Interesting topic. I like your explanation, Sleek.
Now ya'll got my wheels turnin' in all kind of directions.   :o

Online sleek

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Re: How does tiller affect performance?
« Reply #7 on: August 24, 2016, 06:43:36 pm »
Working recurves to me are an example of what a turbo would do. Dont think of them as tips, but as a small high power bow at the tip of another.
Tread softly and carry a bent stick.

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Online sleek

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Re: How does tiller affect performance?
« Reply #8 on: August 24, 2016, 06:46:02 pm »
Interesting topic. I like your explanation, Sleek.
Now ya'll got my wheels turnin' in all kind of directions.   :o


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Offline Justin.schmidt23

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Re: How does tiller affect performance?
« Reply #9 on: August 24, 2016, 07:35:36 pm »
So regarding kinetic energy wouldn't static limb tips like the mollie be the "fastest" design?
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Offline Selfbowman

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Re: How does tiller affect performance?
« Reply #10 on: August 24, 2016, 08:03:31 pm »
I will probably remain in the entire limb working verses the Molly for better cast. Dead wood is dead wood. That being said I am sure there are some who think differently. Also if you have shock you probably also loose cast.  A bow with lots of reflex does sometimes have more shock but has good cast. But at some point there will be a trade off. Arvin
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Offline red hill

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Re: How does tiller affect performance?
« Reply #11 on: August 24, 2016, 08:29:41 pm »
I would think that energy is still being transferred through the static limb tips even if they are not working. As I understand it, the molle's tips work the same as a simple lever.
Has anyone ever slung an apple impaled on a stick? (Showin' age and upbringin' here!  :-X) The stick may not flex but the mechanical advantage provided by the stick as a lever allows a more efficient transfer of energy into the thrown apple.
The movement/transfer of energy outward from the handle to the limb tips seems much like the movement of a wave. Wave dynamics may not apply here but it helps me visualize how a stick and string flings an arrow.

Offline Badger

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Re: How does tiller affect performance?
« Reply #12 on: August 24, 2016, 10:12:38 pm »
  I keep the last 10" or so stiff on most bows, it improves the stored energy. As for shock, the only bows I have ever gotten shock on were bows I used the gizmo on so I could rush and get done.Elliptical tillers will seldom ever be shocky.

Offline willie

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Re: How does tiller affect performance?
« Reply #13 on: August 24, 2016, 10:58:11 pm »
Steve
I have often thought that the best tiller shape might be as you describe. Are you thinking it might be best because hopefully the limb will unwind in a reverse manner upon loosing?

If so, consider a bow limb that is equally strained through out its length. this limb also has the same thickness throughout, so that every part of the limb that has equal width, does equal work. Does tapering the width, (making a pyramid bow) give the progression of bend you desire?

I think when you are tillering for shape with a pyramid bow you are tillering for progressive bend, but how it unbends with arrows of different weights is the bigger question.

willie


Online sleek

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Re: How does tiller affect performance?
« Reply #14 on: August 24, 2016, 10:59:16 pm »
Probably because a circle tiller , the entire limb moves at the same time and stops at the same time. An elliptical tiller allows the tips, the lightest part of the bow, to be the last thing moving. Really that reinforces your suspicuons and my point above. Tips bend first, inner limb last.
Tread softly and carry a bent stick.

Dont seek your happiness through the approval of others