Limb Timing

[Dances with squirrels]

I would be interested in how others define and quantify "proper tiller" and "symmetry".

[son of massey]

With reasonably symmetrical systems it is easier to think of the motion of the bow as a compression of the distance between the nocks and not so much a lateral motion. That way you can mentally keep one nock motionless and consider the motion of the other relative to it. In this case, there is no option other than a perfectly 'timed' return to brace.

The further away from symmetry you go the further away from this perfect innate timing you get. Tillering is designed to (in most cases) closely approximate that symmetry such that timing is not really an issue. (This is a little bit of a mental exercise from here as I am only passingly familiar with Yumis.) The Japanese bows are about as far from symmetrical as you can get. Timing these bows becomes not really an issue though either because the bottom limb moves so little relative to the top limb that there is no difference in timing between 'return' to brace for bottom nock as it barely left brace position in the first place-which means 'timing' itself is not a huge concern in either set of bows-symmetrical ones because it is automatic and unsymmetrical for practicality.

[Del the cat]

Nice post Son of Massey.
I like your trick of moving the frame of reference to one nock.
Del

[Buckeye Guy]

Whooo only 44 post in 9 years and now all this to say !
While the name says son I perceive you are not all that young from those posts
I think you gave a good sumation too , thanks for chiming in!
Guy

[Slackbunny]

I would be interested in how others define and quantify "proper tiller" and "symmetry".

I would define proper tiller as a tiller that equally displaces the stress over all the parts of the bow that are intended to bend.

I would define symmetry as symmetry. Its a pretty concrete concept without much room for interpretation.

[adb]

Symmetry (from Greek συμμετρία symmetria "agreement in dimensions, due proportion, arrangement")[1] has two meanings. The first is a vague sense of harmonious and beautiful proportion and balance.[2][3] The second is an exact mathematical "patterned self-similarity" that can be demonstrated with the rules of a formal system, such as geometry or physics.

[PatM]

 If it's the same "Son of Massey" he may not have many total posts but he has been on here forever as one of the originals from when the message board started.
 He was a prolific poster as a teenager about  12 years ago.
 Many people took a break when the board was off limits unless you subscribed.

[Dances with squirrels]

Hmmm, well, seems to me a bow can be 'properly tillered' while stressing all bending parts equally, OR it can be properly tillered if the outer limbs are caused to bend a little less, or more, for whatever reasons we deem necessary.

Does 'properly tillered' mean tillering a bow to a predetermined measurement at brace, say, 1/8" positive, regardless of unstrung profile and differences In limb shape? Or does it mean something other?

I know what symmetry IS. But when and why should symmetry matter in bow making? If a bow's lineal measurements are identical on either side of the centerline,  it is symmetrical in that sense, but what if that bow has one limb straight and the other has deflex as viewed from the side, should symmetry be maintained in its tiller profile? If not, then what should guide our efforts?

I'm still not convinced timing is unimportant or that all are 'timed' because the string stops both limbs from moving at
approximately the same time. Timing to me is something different. It's more dynamic. Good timing is causing the limbs to 'give' to the string fulcrum equally, so that it, and the arrow nock, comes straight back perpendicular to the handle/shelf. If one limb is stronger than the other, NOT at brace, but relative to the bow hand and string hand fulcrums, it will flex less, and the string fulcrum and arrow nock will move toward the stronger limb, relative to the shelf. Anything more than a wee bit is less than good timing. Imho.

[George Tsoukalas]

DWS, so what happens if the stave has a couple of knots on each limb?
When I tiller knots I tlller them to not bend as much as the rest of the limb. That will certainly affect how the tiller looks.
So what is the stave has some natural twist, it will affect the appearance of the tiller.
I don't always heat out twist. I look at both sides  and take mental snap shot of each to arrive at common ground.
Then there's prop twist ...LOL..which I do not heat out unless excessive.
So you see timing becomes important as does using a few of your other senses for tillering.
Caveat: this is what Ido and have done since the late 80's...not looking for converts to my way of doing things. Gotta go.
Jawge

[Marc St Louis]

Hmmm, well, seems to me a bow can be 'properly tillered' while stressing all bending parts equally, OR it can be properly tillered if the outer limbs are caused to bend a little less, or more, for whatever reasons we deem necessary.

Does 'properly tillered' mean tillering a bow to a predetermined measurement at brace, say, 1/8" positive, regardless of unstrung profile and differences In limb shape? Or does it mean something other?

I know what symmetry IS. But when and why should symmetry matter in bow making? If a bow's lineal measurements are identical on either side of the centerline,  it is symmetrical in that sense, but what if that bow has one limb straight and the other has deflex as viewed from the side, should symmetry be maintained in its tiller profile? If not, then what should guide our efforts?

I'm still not convinced timing is unimportant or that all are 'timed' because the string stops both limbs from moving at
approximately the same time. Timing to me is something different. It's more dynamic. Good timing is causing the limbs to 'give' to the string fulcrum equally, so that it, and the arrow nock, comes straight back perpendicular to the handle/shelf. If one limb is stronger than the other, NOT at brace, but relative to the bow hand and string hand fulcrums, it will flex less, and the string fulcrum and arrow nock will move toward the stronger limb, relative to the shelf. Anything more than a wee bit is less than good timing. Imho.

Symmetry does not always mean in appearance.

The arrow will move towards the top or bottom limb if the nocking point is incorrect

[Badger]

     When I think of limb timing I am thinkng in terms of the arrow going in a straight line when I draw it back and a straight line when I release it. In reality your finger placement when drawing it back will slighlty change where the arrow is situated once you release the string. The arrow is the only thing holding the limbs back when it is accelerating so it won't return exactly as it did when you drew it back. I tiller by pulling it back where I knock the arrow and not where my fingers are going.

[Dances with squirrels]

Exactly George. Knots, twist, humps, dips, refex in one, deflex in the other.... there are plenty of reasons that a wooden bow should NOT be tillered to reveal symmetry, or not have the limb tips travel the same distance, etc.

Marc, to me, the nocking point is 'incorrect' if it is anything other than what I tillered the bow for. I set the nock point at 3/8" above the shelf and then time the limbs by adjusting their relative strength, while pulling from where my string hand will, so that the 3/8" high nock point comes straight back. When the bow's done, I tie the nock point on where planned and it's over. There's no moving the nock point up and down trying to mask built in issues. I find it easier this way. But like George said, I'm not trying to say folks have to do it my way.... just offering food for thought and an option perhaps.

Badger and I are doing nearly the same thing on our trees, we merely pull the string from a slightly different place because i disagree with his 'arrow holding the string back' theory :^)

I may try it his way one day, then mine and see if there is any noticeable difference. Maybe I'll try it on the bow I'm finishing now.

[Marc St Louis]

Well I don't use a tree so maybe that's the difference.  I prefer to tiller with the bow in hand.  That way I can feel what it's doing

[Jesse]

Im not sure if they come home at the same time or not. Makes sense to me that they would. I do know if the limbs are tillered different it will be reflcted on the chronograph.  I like them to both bend the same for the way I shoot. I trace one limb at brace and flip to the other side. If it looks like 2 lines I tiller until its one line. Learning that helped me out a lot.   Jesse

[son of massey]

Wow Pat that is some memory you have got, I did not expect anyone would recognize me.

Del, it is always helpful to simplify a model as far as one can. Sure you miss details, but extremes highlight truisms well.