Author Topic: Tiller shape vs front profile  (Read 17744 times)

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Offline SLIMBOB

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Re: Tiller shape vs front profile
« Reply #30 on: June 25, 2021, 07:55:42 pm »
So I frankly agree with nearly every position put forward here. By that, I think it is sensible to build bows with “principle” in mind, and I think it is just common sense that informs me on this.  It is in no way a must, only a way to marginally increase the efficiency of these bows we make, in certain circumstances. Del and I have been arguing this for 10 years I think.
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Offline PatM

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Re: Tiller shape vs front profile
« Reply #31 on: June 25, 2021, 10:07:28 pm »
Even the term elliptical is a bit odd considering it would really mean a rather whip  tillered bow.

Offline scp

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Re: Tiller shape vs front profile
« Reply #32 on: June 25, 2021, 11:10:38 pm »
It is reasonable to "match" the front profile with the proper thickness tillering. But how are we going to accomplish such a "match"?

"The Mantra: Make inner limbs wide or long enough for virtually no set.
Make midlimbs wide enough for little set. Make outer-limbs and tips narrow
enough for lowest possible mass." (TBB4 p.150)

Can this mantra be applied to all kinds of front profile? At least for all wood self-bows?


Offline SLIMBOB

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Re: Tiller shape vs front profile
« Reply #33 on: June 25, 2021, 11:33:58 pm »
I think in a general sense, yes. It can, or should, be applied without exception. Don’t take set on the inner limbs…we know the consequences if we do. Keep the tips light…no question, this is preferable to heaven tips. You are simply left with the center, and since set is unavoidable, that is where it must happen. We should balance the mid-limb somewhere between too heavy and too light.
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Offline PatM

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Re: Tiller shape vs front profile
« Reply #34 on: June 25, 2021, 11:38:04 pm »
If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.

Offline SLIMBOB

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Re: Tiller shape vs front profile
« Reply #35 on: June 25, 2021, 11:50:23 pm »
That is a really good point that makes you stop and think. The inner limbs can carry more mass because we aren’t moving that mass much at all near the handle. We can afford the extra mass that minimizes any set without much I’ll effect on cast. So the inner limbs would necessarily be under marginally, less strain…I would argue.
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bownarra

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Re: Tiller shape vs front profile
« Reply #36 on: June 26, 2021, 02:31:53 am »
If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.

I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow!  Two different things :)

Pat - 'The typical  circle held against a bent limb orc a gizmo will do that.'     isn't an answer. What's a typical circle?

Offline lonbow

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Re: Tiller shape vs front profile
« Reply #37 on: June 26, 2021, 04:26:04 am »
I´m always trying to find find the right amount of bend for the inner limbs. They should bend as much as necessary in order to take the strain from the midlimb areas but not more. If they bend too much, the bow will be shocky. That´s why I start monitoring hand shock at half draw. If there is to much handshock, I´m removing some wood at the midlimb and outer areas. This ensures a better efficiency of the bow. But there´s also the other way around: I remove some wood from the inner limbs if feel that there´s too much strain in the midlimb areas. Usually it isn´t necessary to remove a lot of wood there because of the good leverage of the inner limbs.

But there is not much oppertunity to play with the tiller, if the bow is very short and narrow for its draw length. In this case, the strain of the wood must be distributed as evenly as possible over the entire length of the bow.

lonbow

Offline Del the cat

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Re: Tiller shape vs front profile
« Reply #38 on: June 26, 2021, 05:10:27 am »
"What's a typical circle"? (quote from Bownarra)
Arc of a circle tiller has only 2 variables.
1. The radius of the circle.
2. What proportion of the circle does it include (e.g 1/3 of a circle or a semicircle)

If you try to define an arc of an ellipse there are a lot more variables, and I've yet to hear or read any actual definition that quantifies how elliptical is elliptical.
Maybe arc of a circle is a bit lazy, but it is vastly easier to interpret.
Del
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Offline RyanY

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Re: Tiller shape vs front profile
« Reply #39 on: June 26, 2021, 05:15:29 am »
If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.

+1. It has never made sense to me that people think the limbs are strained/stressed evenly along their whole length. To me this means the fibers are all doing the same amount of stretching in tension and compression which would result in the same amount of set everywhere. If not then this would mean thicker vs thinner limbs take different amounts of set under the same strain for some reason. I can’t wrap my head around that.

Offline BowEd

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Re: Tiller shape vs front profile
« Reply #40 on: June 26, 2021, 08:22:07 am »
I hear you Ryan.I do know bending it in 1 area too much causes set there if not compensated for with extra wood there.Making a bow according to the amount of power you need and getting most of that from an area on the limb that needs to be compensated for with extra wood there.Leaving less wood in areas on the limbs that take less strain like the outer limbs.
Then it's the discussion of what type of weight arrows are best suited for what type of bows.Whip tillered can shoot lighter arrows faster.Bows working from mid and inner limbs shoot heavier arrows faster.
Exception being short horn bows where their shorter limbs reduce mass considerably because of the composite materials in them.
I might be changing the subject here a bit.Bow making and it's use is such an individual thing there is no 1 size fits all.
« Last Edit: June 26, 2021, 08:27:02 am by BowEd »
BowEd
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Offline Don W

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Re: Tiller shape vs front profile
« Reply #41 on: June 26, 2021, 08:53:08 am »
I think the fact that a limb needs to taper from fade to tip is easy to comprehend. I think once you start to study, learn and experience you get that to much stress causes set, and set is not your friend. But there has to be a better way to explain the correlation between profile and tiller and how to get to an efficient (or more efficient) bow. Even if that means creating categories like hunting, target, general, it's for heavy arrows, for light arrows, etc. We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from. I think the mass theory started down that road, but never got to completion. But there is probably more to it as well. Sorry for the ramble, but I am really trying to wrap my head around this.
Don

Offline PatM

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Re: Tiller shape vs front profile
« Reply #42 on: June 26, 2021, 09:17:14 am »
If you're straining equally and set has to happen, it should take place everywhere the bow is bending then.

I'm not trying to strain the wood evenly i'm trying to strain it optimally for a bow!  Two different things :)

Pat - 'The typical  circle held against a bent limb orc a gizmo will do that.'     isn't an answer. What's a typical circle?

   It's round.  A typical circle is round.

Offline RyanY

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Re: Tiller shape vs front profile
« Reply #43 on: June 26, 2021, 09:42:19 am »
I think it’s helpful to think of these topics in terms of examples and thought experiments. Say you have a pyramid bow and a typical parallel limb taper (American longbow) bow and both have a circular tiller with the same amount of set. Which one would shoot faster and why? (Same poundage/draw length, length, etc. ;) )

Offline willie

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Re: Tiller shape vs front profile
« Reply #44 on: June 26, 2021, 08:55:49 pm »
We seem to interprete speed with efficiency, and speed can be gaged with each situation. So how do I constantly make my heavy hunting arrows go faster? What exact profile do I need to start with and expand from.

Interesting question. With heavy arrows, a bow becomes more efficient, so efficiency gains are harder to tease out of designs.  So maybe just a heavier draw weight? BTW, for me, a bow that is at my upper draw weight limit "feels" better if it is longer.   
« Last Edit: June 26, 2021, 08:59:47 pm by willie »