Too circular??

[Hunter Van Winkle]

I have a question that relates to this issue and the discussion at hand:

What kinds of tillers are there, and what are the differences?

[Del the cat]

I have a question that relates to this issue and the discussion at hand:

What kinds of tillers are there, and what are the differences?

Just my few pennyworth.
Basically:- Circular, whip ended, stiff ended and all shades in between.
There's what I call 'square' too which is one of the classic beginners mistakes... long stiff handle a hinge at mid limb and a stiff tip... one to avoid!
The above assumes a straight bow, if you then add in reflex and/or deflex it changes to look of the bow at full draw.

I hate the term 'Eliptical' as it is too vague and most tiller shapes are elipses of one sort or another (A circle is an elipse with major and minor axis the same length)
A 6' length of 2 x 1/2 will pull into a curve with most bend in the centre, but you could probably fit an elipse to it with the major axis running in the direction of the arrow.
I think people mean an elipse with the major axis running the other way,... it illustrates the possible confusion.
An arc of a circle is pretty unambiguous.
Del

[k-hat]

Del, i bet if i took that pic at 28 instead of 29" of draw the center of the new circle would be right on the nocking point

Your clarification of ellipse vs circle is right on.  It's also why my question was asking if my tiller was edging on being "too circular" of an ellipse.  I guess we expect everyone to know when we say elliptical that we are implying the type of ellipse as you mentioned (long axis perpendicular to the arrow) as opposed to a "circular ellipse".  I suppose it would be correct to say that your tiller oughta be some form of ellipse no matter what the profile!

[SLIMBOB]

Steve Gardner's chapter on "The Mass Principal" in TBB IV (I believe), is the starting point for this topic.  You asked for a more mechanical explanation as to cause and effect.  Great place to begin.  I'm not an engineer and my mathematically challenged little brain gets lost at a certain point on this topic.  I can see that mass placement has an effect on performance, and that is what I keep an eye on.  You asked what the possible effects of this tiller might be over a slightly more elliptical tiller (I agree with Del that the term is misleading)?  Maybe no noticeable effect at all.  If anything, a slight reduction in cast, more set near the handle and more limb vibration or hand shock.  If when shot you see none of these things, then from a PRACTICAL stand point, your good.

[George Tsoukalas]

Excellent! You had to tiller the way you did to get that  draw length from such a short stave. My only concern is that you may experience some stacking toward the late  stages of draw. That happens when the string angle approaches 90 deg which is the case, k hat. Jawge

[Del the cat]

Del, i bet if i took that pic at 28 instead of 29" of draw the center of the new circle would be right on the nocking point

Your clarification of ellipse vs circle is right on.  It's also why my question was asking if my tiller was edging on being "too circular" of an ellipse.  I guess we expect everyone to know when we say elliptical that we are implying the type of ellipse as you mentioned (long axis perpendicular to the arrow) as opposed to a "circular ellipse".  I suppose it would be correct to say that your tiller oughta be some form of ellipse no matter what the profile!

Now that's V interesting because my take on it is you'd need to draw it back about an inch MORE to get the perfect arc of a circle!
I think that really shows how confusing this lot is!
E.G. If the red elipse I drew was stretched down to become a circle, the centre would pretty much be your nocking point, however the bow would be flatter than the arc of a circle.
Heck! I'll just do it and post the pic!
Wow, according to the grid marks in 'paint' the blue is pretty much spot on circular and it sits pretty well on the bow.
I'd just love someone to post what they consider to be a 'better' eliptical tiller so I can see what shape it is. I think the pic shows how subtle some of this stuff is. You can almost fit any shape you want to the curve, that's the advantage of drawing a circle, you can at least measure and quantify the darned thing!
Del

[toomanyknots]

I hate the term 'Eliptical' as it is too vague and most tiller shapes are elipses of one sort or another (A circle is an elipse with major and minor axis the same length)
A 6' length of 2 x 1/2 will pull into a curve with most bend in the centre, but you could probably fit an elipse to it with the major axis running in the direction of the arrow.
I think people mean an elipse with the major axis running the other way,... it illustrates the possible confusion.
An arc of a circle is pretty unambiguous.
Del

...I am so confused...   

[Josh B]

I have to agree with Jawge.  The length of draw that your going for on that length of bow dictates your tiller.  For the best balance of performance and least amount of stack, you nailed the tiller.  If you went for a flatter elipse, it would undoubtedly stack pretty bad.  Great work!  Josh

[gstoneberg]

Wow, it doesn't seem that long ago you stood in my shop and worked on taking that osage stave to a growth ring.  I wish I could claim that I did something that helped take you to where you are today my friend...but I can't.  We just didn't get that far.  But you have progressed really really quickly on your own.   Nicely done, your bow is lovely.  The tiller looks fine to me, more than fine.   I wouldn't change a thing. 

George

[k-hat]

my bad del, i was thinking backwards.  you are correct.  I was thinking that if i relaxed it to 28, it would make a different circle (which it would) but with a larger radius, not a smaller one (which was what i had in my imagination).  As you said, that would put the nock even further from the center of the circle.  Duh

Slim/Del:  My thoughts were along these lines (mechanically speaking from a stress/strain point of view):  if you have parallel limbs that taper in thickness gradually, then the percentage of wood removed per inch to create the taper INCREASES as you move toward the tip (and as we know, changing the thickness a certain percentage has a much larger effect on resistance to bending than changing the width).  This would seem to dictate that if you measured the amount of bend at each inch of the limb, it would INCREASE as you move from fade to the tips.  This would create an elongated ellipse (ie not a circle).  With a constant width taper from fades to tips and uniform thickness, the change in width being constant creates a constant/uniform change in resistance per inch of limb toward the tips.  That would seem to dictate a constant angle of deflection per inch (as opposed to increasing as parallel limbs do) which creates a CIRCLE (ellipse with both foci at the same point... the center).   i havent read Steve's chapter on the mass principle in a while, so i don't know how well this ties in.

I know this is oversimplified, I haven't even considered in this the leverage that each inch of limb exerts on the one before it (from fades to tips) also increases, which may completely negate all of what i said.  Nor have I included what may happen if you have a width AND thickness taper at the same time

All that put aside, if your limbs bend evenly without stiff spots or hinges, and fling an arrow, then you have a bow.  Maybe even a good one.  The rest i think is performance/comfort oriented (which i think is what you were discussing in your previous post, Slimbob), and maybe longevity as well. 

Jawge:  There is a tiny hint of stack the last inch or so, but it aint bad.  At 28" the angle is still well under 90 degrees.  I've put some arrows through, and at the right brace height she feels really good.  Not jarring or anything.  She she seems really fast too, well shooting across the garage anywho    Gonna take her for a spin in the back yard in a bit.

Appreciate ya'lls discussion on this.  I think we often do confuse things by not being real consistent or even accurate with the terms we're using. 

BTW Del: don't some of those short horse bows (mongolian and such w/siyahs) end up with a tiller that is an elongated ellipse with the major axis running along the arrow?

[k-hat]

Appreciate the kind words Doc!  Think i kinda stumbled into it

Thank you George.  You've done more than you realize via our few conversations and interaction here on PA.  I have a great deal of respect for you and your words carry big weight with me.  if you told me the tiller was crap i'd probably just go scrap it and start again   I really owe thanks to a lot of guys here on PA and TG for helping me progress pretty quickly.  It's like being apprentice to a couple dozen masters   So glad i stumbled on this little gold mine a year and 1/2 ago when i got started.

George i know i keep sayin it, but i do look forward to when we CAN get together again and make some shavings!!  Maybe i can bring you one of my wacky hackberry staves and see what you do with it!

[k-hat]

I just put a couple dozen arras through her in the back yard up to about 18 yards.  LOVE IT!!  She is much more accurate than I am , and a pleasure to shoot.  After several draws to 28", I actually didn't feel a hint of stack.  She really sinks them in!  At 6" brace, she is the quietest bow i've made so far.  As my bowyer's knot loosened and the brace came down toward the end, i could tell she got a little noisier, so looks like 6-6.5" is gonna be ideal for her.  I don't think the recipient is gonna have any trouble from the hawgs that get stuck by this little lady

Of course I always fall in love with the ones that have to go away to someone else.  Oh well, i can enjoy her for a little longer while i finish shooting her in and do the finish work.

[SLIMBOB]

I think your above description nails the idea.  When I started making these, there was little thought (at least by me) as to tiller shape, thickness, width taper, mass and movement, blah, blah, blah.  We simply scraped until the tiller was good, and called it a calf-rope.  I made a few whip tillered bows, under weight bows, heavy slow over built bows and a few that were, well, perfectly to my liking.  Without regard to how someone else might feel about it.  If you like it, and it appears as though you should, that's what counts.  I'll bet the recipient loves it.

[Hunter Van Winkle]

Great discussion on tiller. I've made the mistake of tapering width and thickness to start a bow, but it seems to keep an even thickness and a gradual width taper makes the most sense.

[mikekeswick]

Matching tiller shape to the way the limb tapers in width is critical in my opion.
Parallel width then tapering quite suddenly into the nocks will require an elliptical tiller.
Pyramid bows a straight line taper from fade to nock will require a more arc of a circle tiller.
The parrallel width bow WILL have to have a thickness taper in order to bend like a bow. If the wood is tapering in thickness each part out to the nock is getting thinner and can/should bend further - elliptical tiller.
Pyramid bows on the other hand will have little to no thickness taper therefore if the wood is the same thickness it can bend the same amount - circular tiller.

Here's an experiment for anybody who doesn't feel that the above makes sense.
Make 2 bows.
1 that has a straight line width taper and 1 that has parrallel width out to 8 inch from the nock (then tapers into 1/2 inch nock).
Make the 1st bow with an elliptical tiller.
Make the second bow with an arc of a circle tiller.
Then repeat but reverse the tiller shapes.
Which 2 bows shoot the best??

The really important thing with your bow is what does it look like unbraced? Where is the set? All bows will show where they are overstrained.