Tillering bows

[Steve Cover]

Maybe i missed in my search, but I didn't find that answer I was looking for.

Question:  Are bows tillered to have the equal strength on both limbs.

The reason I ask is that most of the bows I've owned, It seems that the lower limb was slightly stronger than the upper.

The reason the knock point is not at 90 degrees??

Anyway, can anyone shed some light on my query, or am I just mistaken?

Thanks,

Steve

[radius]

the way i understand it, the lower limb and upper limb should bend the same, except if the upper limb is longer, in which case it should bend more...english longbow style

[DanaM]

I think most people tiller the lower limb a bit stronger, its called positive tiller.

You should consider investing inThe Bowyers Bible Vol 1-4 its not a huge investment for the amount o0f knowledge that they contain

[Pappy]

On same length lombs I usually tiller them about 1/4 to 3/8 heaver on the bottom limb.
If the top is longer by an inch or so I tiller them even.
   Pappy

[Steve Cover]

Thanks guys,

I was starting to think I was seeing things.

Also, thanks for tip on the Bowyer's Bible, I'll check that out.

Steve

[Hrothgar]

Steve, I suppose the reason most nocks are 45 degrees is because it is closer to the angle of the string when the bow is drawn; although on some flat bow stlyes like the Modoc and pyramid the nocks are often cut in pretty much perpendicular (90 degrees).

[George Tsoukalas]

My limbs are the same length (at least they used to be; getting older now.). I tiller the bottom limb stiffer.The nock point is a little higher than 90 deg. That depends on limb tiller and the split fingered draw. Jawge

[artcher1]

 

"Question:  Are bows tillered to have the equal strength on both limbs."

Here's some of my thoughts on the subject:

Yes, but how you achieve that is by the way you grip your bow.  For example, you're building a bow and know nothing about positive tiller. But you have enough common sense to know that both limbs should feel even strain at full draw. Now, how you grip your bow during the tillering/shooting-in process will determine the amount of positive tiller (or lack there of) you will end up with. Someone who uses a low wrist grip vs a high wrist applies greater heel pressure to their handle causing a need for a stiffer lower limb to achieve even strain at full draw. So a bow designed for a low wrist grip will show a greater positive tiller than the person using a higher wrist design.

A note: some, for their on reasons, like to favor placing more pressure on the upper limb requiring that limb be stiffer. Again, how one grips their bow will determine ones needs. So if you see a bow tillered negative, you can't automatically assume that it's out of tiller.

"The reason the knock point is not at 90 degrees??"

Taking into account the arrow's dia. and the distant that the string nock pushes the arrow nock down (because of string angle) your string nock will most likely be between 3/8 to 1/2" above square on average. ART

[Steve Cover]

"Question:  Are bows tillered to have the equal strength on both limbs."

Here's some of my thoughts on the subject:

Yes, but how you achieve that is by the way you grip your bow.  For example, you're building a bow and know nothing about positive tiller. But you have enough common sense to know that both limbs should feel even strain at full draw. Now, how you grip your bow during the tillering/shooting-in process will determine the amount of positive tiller (or lack there of) you will end up with. Someone who uses a low wrist grip vs a high wrist applies greater heel pressure to their handle causing a need for a stiffer lower limb to achieve even strain at full draw. So a bow designed for a low wrist grip will show a greater positive tiller than the person using a higher wrist design.
A note: some, for their on reasons, like to favor placing more pressure on the upper limb requiring that limb be stiffer. Again, how one grips their bow will determine ones needs. So if you see a bow tillered negative, you can't automatically assume that it's out of tiller.
"The reason the knock point is not at 90 degrees??"
Taking into account the arrow's dia. and the distant that the string nock pushes the arrow nock down (because of string angle) your string nock will most likely be between 3/8 to 1/2" above square on average. ART

Thanks,  That is good information.

I've always used a high wrist grip... (I only own recurves)



In the past, when setting a knock point on a new bow, would shoot fletchless arrows into my target from close range.

I would mark the string at the point the arrow entered the target straight on, and place my knock point there.

Depending on the fistimal, the knock point was always located to place the arrow a variable distance North on 90 degrees.

That helped fuel my interest in positive tiller.

This very old picture (1962) shows the lower limb with less bend than the upper....  I always wondered if it was just an illusion...

I appreciate your detailed answer.  It has laid to rest several of my questions.

Steve

[Del the cat]

It sounds, daft, but I think there must be some confusion over the terms strong, weak, long and short.
The 'working portion' of lower limb is often the same length or shorter than the upper limb.
However the nocking point is often above centre of the string and handle is all below the arrow pass.
This gives some strange geometry, so the terms 'weaker' or 'stronger' aren't necessarilly correct as the two limbs aren't under the same conditions.
The way I see it is the lower limb generally has to bend through a slightly tighter arc, and the whole issue is best resolved on the tiller tree.
If you mount it on the tiller as close as possible to how you will actually hold and draw the bow, and tiller it so that as you draw the string back and forth the handle remains stable and doesn't rock back and forth, then I figure it's gotta be right.
I think it's a matter of doing what works rather than trying to analyse it.... a shed load of physics probably wouldn't help tiller a real wood bow...and ain't that just why we like it?
Del

[artcher1]

Hey Del, if we're dealing with a shorter lower limb then that means that the handle has been shifted down the bow to accommodate for a lighter grip.  Perhaps "off set handle" would be a less confusing term than long or short.

The tillering tree can't account for the hand's heel pressure that's needed to engage the lower limb to compensate for the bracing effect created by the drawing hand being above the bow hand. Only tillering on the tree for the 3-finger under draw would be the closest thing in terms of narrowing the gap between the center of the bow and string. ART

[Del the cat]

Hey Del, if we're dealing with a shorter lower limb then that means that the handle has been shifted down the bow to accommodate for a lighter grip.  Perhaps "off set handle" would be a less confusing term than long or short.

The tillering tree can't account for the hand's heel pressure that's needed to engage the lower limb to compensate for the bracing effect created by the drawing hand being above the bow hand. Only tillering on the tree for the 3-finger under draw would be the closest thing in terms of narrowing the gap between the center of the bow and string. ART

Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately.
Mine has a radiused block with a thin rubber covering, I place the bow on it at the point where my hand pressure will be, The string is drawn back by a two pronged hook which approximates the with of  my fingers under string pressure, it is very noticeable how much differnce there is between that and supporting the bow dead centre and pulling the string back dead centre.
Maybe you can't simulate a very heavilly contoured grip like on a recurve, but even so, the force should pretty much come through a single point (or the geometric centre of a pressure area).
If the hand is having to provide forces to stop one limb coming back more or less than the other, I'd say it is tillered wrongly, as surely the bow hand should be relatively 'soft' (relaxed)?
It's a good discussion point, and one of the probs is expressing what one actually means!
All just my opinion of course...I'm not trying to be dogmatic (or catmatic?).
Del

[artcher1]

"Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately. "

Can't argue you point Del....................cause I use to do things very similar to you. So I know exactly what you're saying. But through the knowledge and experience I gained over the years I since moved on with a better understanding of how things work. Again, sorry I can't argue you view...................ART

[Del the cat]

"Sorry but I dissagree...The tillering tree CAN simulate the heel pressure fairly accurately. "

Can't argue you point Del....................cause I use to do things very similar to you. So I know exactly what you're saying. But through the knowledge and experience I gained over the years I since moved on with a better understanding of how things work. Again, sorry I can't argue you view...................ART

I'm interested in what other people think feels right.
Are you saying you like to feel the lower limb pulling/pivoting the bow into the heel of your hand?
I can see that might feel 'right', I've just not tried it myself... (yet  )

PS. I've only just spotted your original post which makes it clear what you mean...sorry.
Del

[El Destructo]