Tillering

[Walt Francis]

Often people want full draw pictures of laminated wood and glass bows.  When learning to build wood laminated and glass bows I was taught to tiller my limbs by timing them throughout drawing process.  With these type bows, the lower limb is usually a little stiffer then the upper (tillered for split finger), reflected by the string being closer to the lowest part of the fades/limbs on the lower limb then on the upper.  Anyway, in my experience if the limb timing is correct you rarely get the perfect symmetrical arch on both limbs that many use to judge a properly tillered selfbow (that is a debate for another time).  Admittedly, I have only built a little over 30 laminated bows (21 glass and 14 all wood) but the amount of hand shock is less, smoothness while drawing the bow is increased, and arrow speed faster for the same draw weight, when ignoring the full daw profile picture and using limb timing as my guide.  You still need to tiller each limb to a, for lack of better words, “A Smooth Arch”, eliminating any sibilance of a hinge, but the arch of each limb is different; Not much, but still different.  

My question is what method do you use for judging tiller on laminated wood and glass bows and why?

I know there are other methods that some use, lets hear about those methods and your reasoning for using them.

[Stiks-n-Strings]

Looking forward to what I can learn on this discussion.

 Stiks

[NTD]

I tiller for an even bend throughout the limb, because that's the way I've learned. I am open to other ideas but have never heard a convincing reason to do so.  I also build symmetrical bows.  I've seen/read very little about how to tiller like you mentioned.  How exactly do you tiller for timing?  High speed video?

[Art B]

A full draw profile should only verify or confirm proper limb design I would think Walt. And using even limb strain at full draw to verify for best possible timing.

But I know what you're saying about the arc of one limb being slightly different than the other sometimes. But should it be? Can it be prevented? Could better limb timing be achieved by both limbs showing an even arc?

Boy, everyone's different when it comes to gripping a bow. Using proper grip per design would go a long way in eliminating a lot of problems in this area.

But to answer your question, and since I try to apply even strain to both limbs at full draw, I look for an even arc for both limbs when drawn. And when I do get it right (not all the time), I know I can keep my tiller (usually the thickness of the string) very close and maintain that over the life of the bow (selfbows). I shoot split fingers with arrow passes from 2" to 1 1/2" above center.

This bears repeating, there's no better way, IMHO, to achieve best limb timing, then to properly grip a bow per it's design/arrow pass layout ......Art

[Roy from Pa]

Walt, by timing your limbs, are you speaking of the horizontal lines drawn on the wall behind the tillering tree? And having the limbs bend equally?

[NYArrow]

Interesting thought.

[John Scifres]

I'm all for eliminating variables when I tiller.  That's why I have gravitated to Torges' fulcrum concept.  I have a rolled up leather pad at the top of my block of my tiller setup.  I place the center of the bow on the apex of that pad.  That makes it a teeter totter of sorts.  
 

Then I mark the center of my tillering string.  This changes depending on the length of the string which shortens as I get closer to full brace height.  I place the hook of my tiller pull rope on the center point of the string.  

A well balanced bow does not rock on the teeter totter.  In the end I prefer an arc of the circle final shape with stiff tips.  I think it loooks better but it only works for the type of bows I build.  The radius of each limb does differ slightly though.  My limbs are equal lenght if you consider the center of the bow the beginning of the limb (how could it be otehrwise?).  But on rigid handled bows, the wroking portion of the bottom limb is shorter.  

I acknowledge that some people hold their bows wrong but if you all did everything correctly like me, you could elimiate some variables.

But that is only the starting point for tillering.  Final tiller begins and ends in the hand.  If it draws poorly and shifts in my hand or shoots like crap with handshock or torquing, something is wrong and I work from then on mostly without the tree until it feels pleasant in the hand.

[George Tsoukalas]

Walt, you said lam and glass bows. I never built any of those. Not even a wood backed bow. I don't heat wood much and try to work with it as much as possible in it's as is condition. I'll heat if I have to make limbs match but that's about it. I kind of don't follow the crowd on that. So having told you that.  Here's what I do. I floor tiller and then long string tiller. I try to match the tiller on both of the limbs so it is not really a case of 2 separate tillers on each but that may be accurate enough a description. I let the stave determine the tiller pattern it wants. I have to since I don't heat it into submission. Timing is everything. The rope and pulley will show the limbs bending, flexing and returning in unison. If not I fix it. I tiller to draw weight 1 inch shot of my draw and shoot it in. Looking for a balanced tiller as I draw. No tipping. The drawing of circles and arcs is a nice way to look at tiller until your eye is practiced enough to not need it. I don't use it. That's the way I've made'em for me and mine for years.    Jawge

[Art B]

I also consider limbs as starting in the center of the bow John. To understand limb timing, balance, equal limb strain, and the one thing folks fail to talk about, equal limb mass. That starts at center also.

So to achieve best timing, one could say that good balance in the hand at full draw, equal limb strain and equal limb mass is what one should strive for. And if one subscribes to that notion, then no matter what configuration of limb lengths we use, it just comes down to properly gripping the bow if those steps are adhered to that I mentioned earlier.

In theory, and if this critera is met, neither limb would show more stressed (asymmetrical) other the other. Following this line of thinking throughout the building process, will in the end, produce the best possible balance and timing IMO........Art

[SEMO_HUNTER]

I agree with your explanation Art, mainly because it makes the most sense to me and that's actually how I have made my self bows so far. That's also the reason why I keep my intended grip position as close to the actual center of the bow as possible. Then the arrow goes as close as possible directly above my hand. I didn't figure this scientific marvel of an equation up myself, but mostly through what works and what didn't work. I guess you could say I just stumbled into to it by not knowing any better?
Well not actually that blindly, I have put alot of thought into it and that's what made sense to me, so that's how I built my bows and so far for me it has worked just fine.
I have found that shooting directly off the top of my knuckle as closely as possible has worked the best when the center of the bow is planted firmly in the crotch of my grip between my thumb and index finger.

Right or wrong, that's just the results I've experienced.

[Walt Francis]

Everybody, thanks for the input.

NTD, I wish I had a high-speed camera; it might help answer some of my questions.  Then again, it would probably create more questions then it answered.

Hova, you are in good company, I know several bowyers that make some fine shooting bows that used the same reasoning to design and build their bows.  I also like your reasoning because it is similar to mine and you arrived at same conclusion I did about ten years back.    

Let’s define timing, at least as I understand it:

 When the limbs reach the end of the power stroke, with the same amount of force, at the same time, they are in synchronization and timed.  

This is not a perfect definition and is open to suggestions and refinement.

Without a high-speed camera, the only method I know to check the timing is by feel.  When the excess forces exerted by the limbs at the end of the power stroke are out of synchronization, they cause a different oscillation in each limb, and is felt in the hand as excessive hand-shock.  Regardless of the timing, there is always some hand-shock when shooting an arrow; it is just greater if the limbs are unbalanced.  


Art, Your thoughts regarding energy and mass is the main reason I wanted to limit the discussion to laminated bows.  As you stated, the way somebody grips the bow makes a huge difference on the way a bow performs.  I saw a shooting seminar by Fred Asbell once and he used a 15# bow to demonstrate the effect different grips had on the bow limbs; it was significant.  My thoughts are close to yours, for a bow with equal length limbs and the riser centered on the bow.  In theory, if the pressure from the string and the throat of the grip are both centered on the string and bow, a perfect tiller, and timing, would have limbs with identical profiles.  If the pressure point of either the string or grip shifts then the timing and tillering will change.  I think bowyers stiffen the bottom limb and/or make it shorter, to help bring the timing of the limbs closer.  Adjusting the brace height fine tunes the timing and brings them even closer to synchronization.  That is why every bow has a “Sweet Spot”, or the best brace height, where hand-shock is minimized for that bow.

Enough rambling, back to the point of my original post: Why do some ask for a full draw picture of laminated bows?  If the accepted practice is to either stiffen the bottom limb and/or make it shorter the profile of the bottom and top limbs will be different, unless the limbs are out of time/synchronization.  If the lower limb is shorter, the arch will be different then the upper.  The same is true when the lower limb is stiffer.

John, you reached the same solution as myself, with all my bows, glass, laminated wood, or selfbows, I first tiller to symmetry (because it is often close to the correct timing), and then final tiller by feel.  Before I started making glass bows, my thinking was the tillering was going to be a lot easier then with selfbows; in some respects, it is (now that I got most the forms fine-tuned).  However, I still find myself having to final tiller by feel.  The full draw profiles of my bow are usually close, but never perfect, so I started thinking it was my design.  Wanting to check if it was me, I started looking at my glass bows made by others (over 30) and only two of them had a symmetrical full draw profile.  Both these bows have more hand-shock then the majority the other bows.

[John Scifres]

Many years ago, Rusty Craine posted a tiller setup which consisted of the familiar pull rope but on the top, instead of a stationary block, he had another rope with a loop to hold the bow at it's fulcrum.  When this was pulled, it was very obvious if the bow was unbalanced or if it went every-which-way upon drawing.  I have long debated setting up something similar.

As for timing, I agree it is most obviously felt but it can also be seen when drawing the bow in a tiller setup.  True, the limbs return in unison when timing is on but they also draw in unison.  Deviations from balance are fairly obvious with a fulcrum tillering setup but I bet they are really obvious with a setup like Rusty devised, especially when videoed and played in slowmo.

Again, many years ago, as I was doing the very first online buildalong I ever did, 1998 I believe, Jim Fetrow suggested weighing the limbs independently to judge balance and potential for good timing.  I was too green to understand what he meant at the time.  But I do now.  Even if I don't regularly follow the advice.  

But we tailor our bowmaking to suit our goals, lifestyles, moods, and personalities.  One man's balance is another's overanalization    

[George Tsoukalas]

Walt:"Let’s define timing, at least as I understand it:

When the limbs reach the end of the power stroke, with the same amount of force, at the same time, they are in synchronization and timed. "

That's half of it. They must also return synced. Jawge

[Walt Francis]

George,
When mentioning the end of the power stroke, I am thinking of the point when the arrow leaves the string and all the remaining energy is transferred/remains in the bow and is dissipated by vibration.

John,
“One man's balance is another's overanalization   “, I don’t think that is really a word, but it is a good description of me at times.
I remember Rusty’s tillering setup and “overanalization describes my exact thoughts, at the time.  I have always leaned towards the KISS principle, unless it adversely affects feel and performance; which I believe a perfectly symmetrical bows does.

[John Scifres]

I don’t think that is really a word  

You do remember Rutsy's spelling prowess...right?

[Art B]

It's one thing to talk about limb timing, but quite a different story to actually experience it.

A perfectly timed bow would have the arrow in the center of the string and the bow. So that's not going to happen with us having to grip the bow below the arrow.

Tim Baker come up with a method some years ago that would give us a small taste of what we're missing concerning true timing. Quite the eye opener!

Take one of your bows, mark up 5/8 of an inch from the center of the bow for the arrow pass, shooting split fingers to where the pressure of the middle finger aligns very close to the center of the bow. Bow is gripped with "thumb" only.

First thing you'll notice is a faster arrow. Second thing that's noticeable is a quiter bow. Once you experience this, you really get a better understanding, and the added benefits of better timing.........Art

[Walt Francis]

Oh ya, he is always good for some good ones.  My favorite saying of his is "sinew is magic".

[Art B]

Don'y know many of Baker's sayings, but sinew certainly isn't magic, but useful to say the least.

Wasn't referring to any of his sayings Walt, just describing something that I feel is useful as a learning tool........Art

[John Scifres]

I think Walt was talkin' about Rusty  

[George Tsoukalas]

That's a Rsuty saying. Tell you what. You'll now if your bow is not timed. Limbs bending and flexing in unison make for little hand shock. Jawge