Where did positive tiller come from?

[huisme]

I've always thought it's because when you're crouching and going through the bush stalking brey you want most of what you're trying to carry with you in front of you and in your visual range, and when you draw you want the bottom limb off the ground which is easier if it's shorter.

[dwardo]

I have started to notice recently that the tillerboard is only good upto about 22 and a bit inches. After that it has to be all by hand and feel.
If I rely to heavily on the board (knackered elbow) then i tend to come out top limb a tad stiff,

[Marc St Louis]

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 don't think so Pat

[PatM]

Well take a bow(with a longer top limb) that sits with 1/8 positive tiller and draw a line from the short limb tip to a corresponding point on the upper limb.
 The "string" will now be  the same distance from the belly of mid-limb on both sides.
 If you trace the arc it will match if your ability to execute an even bend is good.
 To actually show true positive tiller, your limbs would have to be even length. I would believe it then.

[bow101]

Marc could you clear this up...?   need an experienced bowyer to get this positive thing settled.......

[huisme]

I sat here for a minute thinking, "Waaait, I'm not one to clear up anything like this. I'm a physics guy, but this is history. I haven't posted anything exceptional about history, have I?"

Then I remembered I share the name with a certain bowyer I'm sure you've heard about

[PatM]

Let me reiterate that I only mean my theory applies if your limbs are of  unequal length and the positive tiller is minimal. I would think if your upper limb is an inch to 1.5 inches longer the positive tiller would need to be over 1/4 inch before it could be said to be as a result of a true greater bend plus the limb length differential.
 

[lostarrow]

I will have to check out that blog ,Del.

 PatM. The question I'm after is why would you make the top limb longer and try to compensate by adjusting tiller on the bottom?  Does it not make more sense to make the dimensional center of the bow the actual pivot that bears on your bow hand. If you shoot three fingers under (I just happen to) your middle finger lays in perfect relation to the center of the bow, with the arrow resting about 1-1/4" above  on both the bow and the string. Then measure out your desired distance for  handle and match the distance above for arrow pass /sight window . Start the fades at the same distance from that center and make the limbs the same  dimensions .(length ,taper etc. )  If this is the case, the bottom limb should be equal to the top. Everything is symmetrical both string and bow.
     The only reason I can think why you would need a positive tiller is if you placed the arrow in the dimensional center of the bow, which would then make a Mediterranean release line up better.  (not as perfect as the former method with the shape of my hands, but I don't think enough to make a difference). You now talking about a difference of say 1" - 1-1/2"

   Pat got me thinking with his longer top limb statement (which I understand what you are saying completely , there's no argument here ,to your statement) The positive tiller / stiff limb on the bottom only seems to make sense , if you are placing your arrow in the center of the bow, instead of your hand.

     So that leads to the next question.
1:Who lays out their bows  with the arrow in the center , and who lays it out with your hand in the center.

2: Also , is there a good reason to place the arrow in the dimensional center of the bow? ( as I see it , there is no way to draw , short of a mechanical release  or one finger under and one over ,that will put the arrow in the  apex of the string angle)

[PatM]

Without getting into that endless circular argument Tim Baker used to always bring up, I think a bow with a longer upper limb is just far more forgiving.
 There is just no way a person can actually shoot a bow from the exact center without a release and a shelf on the right side at mid bow.
To take it to an extreme you can string up an untillered  bamboo pole bow and shoot it very well with  most of the bend taking place only in the upper limb. If you flip it over and shot it with the short stiff limb up it just won't work the same.

[lostarrow]

  That's what i'm saying ,Pat. If you are shooting with the arrow above center anyway, why not lay the bow out with your  one hand in the center of the bow and the draw hand in the center of the string. Making both limbs equal length and tiller.

 When you layout a bow , how are you doing it?

 I know the quote from Tim Baker was used to back your statement , but ,once again  anecdotes and common practise without evidence to back it up , will only serve to hinder our progress. From reading through Del's thread ( the inspiration for this one), it seems that a lot of people are using a positive tiller with no solid basis as to why and how much. As did I .I'm not faulting anyone but myself ,for not looking into it sooner. There is still a lot  to learn and relearn about our chosen craft.

[lostarrow]

@ 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

 

 So ,Del,  the bottom limb was 2" shorter, from fade to nock?

[PatM]

  That's what i'm saying ,Pat. If you are shooting with the arrow above center anyway, why not lay the bow out with your  one hand in the center of the bow and the draw hand in the center of the string. Making both limbs equal length and tiller.

 When you layout a bow , how are you doing it?

 I know the quote from Tim Baker was used to back your statement , but ,once again  anecdotes and common practise without evidence to back it up , will only serve to hinder our progress. From reading through Del's thread ( the inspiration for this one), it seems that a lot of people are using a positive tiller with no solid basis as to why and how much. As did I .I'm not faulting anyone but myself ,for not looking into it sooner. There is still a lot  to learn and relearn about our chosen craft.

Tim was actually insisting on the equal limb length /tiller and shooting from the center of the bow.
 I like a bow that points with the same natural angle that your extended clenched hand will naturally have.  A more Yumi like tiller with an upper limb that bends more and tilts the bow forward a fraction.]
 This means an upper limb about two inches longer, placing the arrow very close to the dimensional center.

[Del the cat]

@ Lostarrow.
I've just popped out to the grage and measured it. The lower limb is about an inch and a half shorter.
Del

[mikekeswick]

It really is very simple.
You put different forces on the bow limbs when you draw the bow by hand.
Bow hand pressure point and the point where you actually pull the string from are what you need to think about and their relation with where actual measured center is on the bow.
Tiller you bow to bend evenly and be balanced at full draw and the lower limb needs to be stiffer.
It really is as simple as that.
I don't understand what you are all talking about! Just tiller the darned bow to be balanced in the hand at full draw. 
This is, always has been and always should be the way to tiller a bow.
I'm saying no more.

[Del the cat]

I'm saying no more.
Oh come on Mike, I'm sure if we prod you a little, you might  
I think the (IMO naive) practice of clamping a bow on the tiller and/or supporting it and drawing it from the geometric centre causes trouble.
But we all have our ways of doing stuff.
Del