Author Topic: Where did positive tiller come from?  (Read 7245 times)

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Offline lostarrow

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Where did positive tiller come from?
« on: January 31, 2014, 11:29:28 am »
  Del's post "Where do they break" lead to some interesting discussions .(some ,very heated) Glad to see things were hashed out quickly . Just goes to show the   admirable character  of  those involved.

 Without getting too heated , what are the thoughts and reasoning behind the practice of positive tillering , and possible origins . I have a few Ideas , but will keep them to myself for a bit ,so as not to influence  other's theories.  Sort of a discussion on past principles  that may or may not work  in present day with current knowledge.
  (I didn't want to hijack Del's post)

Offline Dances with squirrels

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Re: Where did positive tiller come from?
« Reply #1 on: January 31, 2014, 12:18:31 pm »
I think how it got started will be hard to figure out... and largely open to speculation.

Predetermining 1/8" positive tiller, or ANY tiller measurement at brace height is not the best way to build bows, IMO. I tiller so that the limbs are bending in harmony, held as the archer will hold it, and its profile at brace s the result OF tillering/timing not a guide FOR it. Doing so avoids a lot hurdles down the road, especially with bows from odd shaped staves and such.
Straight wood may make a better bow, but crooked wood makes a better bowyer

Offline RBLusthaus

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Re: Where did positive tiller come from?
« Reply #2 on: January 31, 2014, 12:26:52 pm »
Not sure about its origin, but when I tiller a bow, I have not usually determined which end will be the top and which the bottom.  I generally keep flipping the bow, end for end, throughout the tillering process till near the end, when I am forced to decide which will be the top.  That decision is usually based on string / handle alignment, but if it is good both ways, I would make the weaker limb the top, since it does not work as hard.  I do not intend to tiller a weaker limb, but there always is one. 

Russ

Offline PatM

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Re: Where did positive tiller come from?
« Reply #3 on: January 31, 2014, 12:57:43 pm »
In most cases positive tiller is solely as a result of a longer upper limb. There is actually no increased bend.
 That's the real answer.
 

Offline Del the cat

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Re: Where did positive tiller come from?
« Reply #4 on: January 31, 2014, 01:10:35 pm »
I used to think it was bunkum, and even argued to that effect...
E.G. I'd  say "If both limb tips come back the same distance at full draw. The lower limb is shorter, therefore it must be bending on a tighter radius (assuming a simple arc of a circle tiller).
If it bends on a tighter radius for the same applied force it must be weaker, not stronger!".

Of course you've all spotted the flaw in the argument... the applied force on the two limbs isn't the same :(.

My guess is some early bowyer noticed his lower limbs taking excessive set or going rubbery on him, so he then made 'em a tad stiffer.
IMO The best bowmaking is based on experience and observation. The maths is useful as a tool in some instances, but we should be aware that our ancestors did fine without it.

My first encounter with the need for a bit of positive was when a fully tillered and well shot in Ash primitive with wide flat limbs suddenly went weak on the lower limb. If I hadn't seen it with my own eyes, I wouldn't have believed it. It was a very chastening experience, and I sought solace with the community here :laugh:

I think positive tiller is more of a shorthand measurement rather than an aim in itself. I've even had Robert Hardy himself, tell me one of my bows was "built upside down"!
It had negative tiller because I'd put the naturally deflexed limb as the lower one. I popped off the string and showed him. I didn't actually argue, as I felt it right to show due deference to the man :)

Target archers adjust their take down contraptions to have a bit of positive tiller, presumably it has some value in tuning the bow. It can't be about safeguarding the limbs on their bows as they are waaaay over designed and could be overdrawn to hades and back with no ill effect.
It tickles me when they say they are 'tillering' their bow ::).
Del
« Last Edit: January 31, 2014, 01:18:56 pm by Del the cat »
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Offline lostarrow

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Re: Where did positive tiller come from?
« Reply #5 on: January 31, 2014, 01:29:39 pm »
Sorry guys, after thinking about it ,I realised how silly it was to hold back an opinion in a discussion forum. ::) These are all our opinions after all, and I'm open to any and all of them.

      My concern is that we may be misled (unintentionally) by conventions of the past, without  allowing for different circumstances of our own time and place.
    Our ancestors lacked the benefit of social media and shared knowledge from a wide spectrum. Couple that with a guild that needed to keep their secrets for matter of job security and you wind up with pockets of disconnected information and lost knowledge. A man would learn as an apprentice from his master (often only one)  As we all know, not everyone is a good teacher and  even if you know something , you may not be able to express it.  Even if you do express it , it may not be  fully understood. How many times has  it happened that you were told to do something a certain way  just because it worked?
     The problem here is ,that tidbit of info might work in that instance  with that piece of wood ,in that climate ,with that design for the intended purpose. If  utilised but not understood, that information could quickly become the "common practice" If you are an apprentice and cranking out war bows  designed for a specific purpose  you would likely carry that " common practise" to be a hard fast rule.
      Reverse engineering might also come into play . Looking at a successful  bowyer's bow and taking measurements and trying to mimic it  could lead to  copying a flaw  that may be due to circumstances other than design, such as abuse , poor storage conditions , change in climate  etc.  Just about anyone who asks how to make a bow, has the mistaken impression that you form the bow to have a curve (when they are really looking at the set.  They think it is the cause not the effect.
   I guess what I'm  trying to say is," Knowledge without understanding,  is not wisdom".  (feel free to embroider that on a pillow :D) Without  understanding how something works , information can be next to useless or in some cases ,detrimental.  The English longbow made from yew benefits from  certain design characteristics that result in utter failure if applied  to other species or designs . We know this because of our advanced knowledge of cell structure and physics. Our very ancient ancestors may have learned by trial and error.
   I would like some hard facts to help me evolve, and become a better bowyer.  I have  heard more times than I can count that the bottom limb needs to be stronger because it is under more stress, usually followed up by " it's a fact " or "physics proves it ". I don't feel this is always the case.
 
   Can someone prove to me that the bottom limb is under more stress?  Please state your arguments /thoughts without fear of offending . This is a discussion to promote advance . I will not be offended and don't intend to offend, but will not accept "Old adages" or" Common knowledge " without at least a guess as to why. We are all here to learn.

Offline lostarrow

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Re: Where did positive tiller come from?
« Reply #6 on: January 31, 2014, 01:31:41 pm »
In most cases positive tiller is solely as a result of a longer upper limb. There is actually no increased bend.
 That's the real answer.
  Good point...................... why is the upper limb longer?

Offline lostarrow

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Re: Where did positive tiller come from?
« Reply #7 on: January 31, 2014, 01:35:12 pm »
I used to think it was bunkum, and even argued to that effect...
E.G. I'd  say "If both limb tips come back the same distance at full draw. The lower limb is shorter, therefore it must be bending on a tighter radius (assuming a simple arc of a circle tiller).
If it bends on a tighter radius for the same applied force it must be weaker, not stronger!".

Of course you've all spotted the flaw in the argument... the applied force on the two limbs isn't the same :(.

My guess is some early bowyer noticed his lower limbs taking excessive set or going rubbery on him, so he then made 'em a tad stiffer.
IMO The best bowmaking is based on experience and observation. The maths is useful as a tool in some instances, but we should be aware that our ancestors did fine without it.

My first encounter with the need for a bit of positive was when a fully tillered and well shot in Ash primitive with wide flat limbs suddenly went weak on the lower limb. If I hadn't seen it with my own eyes, I wouldn't have believed it. It was a very chastening experience, and I sought solace with the community here :laugh:

I think positive tiller is more of a shorthand measurement rather than an aim in itself. I've even had Robert Hardy himself, tell me one of my bows was "built upside down"!
It had negative tiller because I'd put the naturally deflexed limb as the lower one. I popped off the string and showed him. I didn't actually argue, as I felt it right to show due deference to the man :)

Target archers adjust their take down contraptions to have a bit of positive tiller, presumably it has some value in tuning the bow. It can't be about safeguarding the limbs on their bows as they are waaaay over designed and could be overdrawn to hades and back with no ill effect.
It tickles me when they say they are 'tillering' their bow ::).
Del

 Also good info  drawn from a great deal of experience! ........... missing a bit of info to complete the picture. The ash bow.... was the bottom limb different in dimension to the top in relation to where the bow was held and string was drawn? I would think that would make all the difference in the world, no?

Offline Bryce

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Re: Where did positive tiller come from?
« Reply #8 on: January 31, 2014, 01:45:54 pm »
In most cases positive tiller is solely as a result of a longer upper limb. There is actually no increased bend.
 That's the real answer.
  Good point...................... why is the upper limb longer?

This way the actual center of the bow rides in the croch of the hand and when drawn, balances very nicely.
Clatskanie, Oregon

Offline bow101

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Re: Where did positive tiller come from?
« Reply #9 on: January 31, 2014, 01:48:16 pm »
In most cases positive tiller is solely as a result of a longer upper limb. There is actually no increased bend.
 That's the real answer.

I  allways thought that the bow was built with both limbs been equal length.  So if a bow is 70" overall, I mark it 35" then go about 1 1/2" or whatever above center for my arrow rest/shelf. 
So this makes the lower limb longer, but then again I guess it depends if you are shooting split or 3 under..?
But technically the bow limbs are equal because the handle is built or glued on from center point.
 
"The privilege of a lifetime is being who you are."  Joseph Campbell

Offline lostarrow

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Re: Where did positive tiller come from?
« Reply #10 on: January 31, 2014, 02:37:47 pm »
 If the pivot (where you rest the crotch of your hand ) is the dimensional center, and your arrow is placed on the string  correspondingly higher to match where it will be resting above your hand,........... and you have the same length  above and below your pivot to where you lay out the working limbs (fades on a stiff  handle)......... and you are pulling the string in the center..... why would you make one limb longer than the other? Any thoughts?It's not a trick question bit will lead to others (I hope)

       The difference between split finger and Mediterenian  release is a matter of a finger width that can be taken into account with layout of the fades ,which would then make the start of the bottom working limb 1/2" or so farther from the fulcrum. Seems easier than trying to compensate with limb stiffness.

   I like where this is going! Thanks for the positive responses guys!

Offline 4dog

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Re: Where did positive tiller come from?
« Reply #11 on: January 31, 2014, 02:43:28 pm »
In most cases positive tiller is solely as a result of a longer upper limb. There is actually no increased bend.
 That's the real answer.
  Good point...................... why is the upper limb longer?

This way the actual center of the bow rides in the croch of the hand and when drawn, balances very nicely.

this is how i do it,,right or wrong..center of bow in the center of palm..3 finger split..for what that worth..lol
"SET" is always there !!!

Offline Carson (CMB)

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Re: Where did positive tiller come from?
« Reply #12 on: January 31, 2014, 03:44:58 pm »
It is all about string angle.   8)
"The bow is the old first lyre,
the mono chord, the initial rune of fine art
The humanities grew out from archery as a flower from a seed
No sooner did the soft, sweet note of the bow-string charm the ear of genius than music was born, and from music came poetry and painting and..." Maurice Thompso

Offline Del the cat

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Re: Where did positive tiller come from?
« Reply #13 on: January 31, 2014, 03:47:28 pm »
@ Lostarrow.
The whole build along including tillering videos is on my blog.
Starts here:- 29th July
http://bowyersdiary.blogspot.co.uk/2010/07/change-of-tack-some-design.html

The "I can't believe it" moment is here:- 9th October!
http://bowyersdiary.blogspot.co.uk/2010/10/i-cant-believe-it.html
Short answer, I think the arrow pass is 1" above centre and the upper limb starts there the lower limb starts about 3" below centreline.
Del
Health warning, these posts may contain traces of nut.

Offline burchett.donald

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Re: Where did positive tiller come from?
« Reply #14 on: January 31, 2014, 04:26:39 pm »
  This is or could be a complicated subject...For me it is balance. If I tiller a bow to feel well balanced on the draw it normally is positive on the top limb. What causes this is my drawing fingers are above center on the string. The top limb has to be weaker/positive for me to achieve balance drawing and at full draw. Thus positive tiller is born for me. I don't think it's a rule just more of a result. I might add measuring tiller can be difficult to do with all the asymmetrical shapes limb thickness and whop-de-doo's. My finished tiller is definitely done by feel and balance.
Genesis 27:3 Now therefore take, I pray thee, thy weapons, thy quiver and thy bow, and go out to the field, and take me some venison;