Help on warbow/longbow tiller - first post! / now with pics...

[Del the cat]

   I have always felt the same way about the word elliptical being ambiguous. If I were to describe my preferred tiller I would say I like the middle 8 or 10" slightly stiffer and I like the last 10" of the limb barely flexing. I find if I get too circular the bows tend to feel more shocky.

Well, it's easy to define how elliptical the desired shape should be. Essentially, a circle is an ellipse with two identical (horizontal and vertical) radii. A flattened ellips has the horizontal radius longer than the vertical one.
Show us your ideal tiller profiles for ELBs, and we can easily deduce the proportions of the vertical and horizontal radius of the ellips. Say it is 1 to 1.2, we can henceforth define the ideal elliptical shape as 1/1.2, and we can also look at a tillering pic and see how much it deviates from circular, and how much from the ideal ELB (or whatever bow type that should have elliptical tiller, like holmegaards and mollegabets).

Yes it's easy to define an ellipse... BUT
That doesn't answer the question of how far round the ellipse the curve should go! 
You can take your ellipse and use a section from the centre which will look almost like an arc of a circle. Or if you take a full half of the ellipse it would be ridiculously whip tillered.
(refer to the pics in my earlier post).
Del

[joachimM]

Granted Del.
You also need the angle of the arc each limb should cover at full draw, or the ratio of the arc covered by the bow to the circumference of the ellips.

[willie]

That doesn't answer the question of how far round the ellipse the curve should go

if your long axis is fixed at a given ratio to your bow length, the how far around question becomes irrelevant.
just adjust the minor axis to match the curve, no matter how far you have drawn the bow.

[penderbender]

I do this a lot while checking tillering pics on my phone. I just use my coffee cup and tilt it til I see what I want. Cheers- Brendan

[Del the cat]

That doesn't answer the question of how far round the ellipse the curve should go

if your long axis is fixed at a given ratio to your bow length, the how far around question becomes irrelevant.
just adjust the minor axis to match the curve, no matter how far you have drawn the bow.

Yup, that would do it....
Just give us the numbers...
Del

[FilipT]

For that hazel bow I am currently making I liked to use AutoCAD to trace lines and see where it bends more and less. Then I compared what the software showed to what bowyers said and it's basically the same.
Of course, con of this is that you have to have this software, but since I am studying mechanical engineering it was logically for me to use this, instead Paint for example.

[willie]

the number for the last bow I tillered this way was   1.2
BTW, Joachim mentioned the same number as an example when comparing the ratio of the long axis to the short axis, but for the sake of clarity, I am using this ratio to proportion the long axis of the ellipse to the bows overall length.

for instance, in the case of a 70" bow, the long axis of the ellipses I drew on my backboard were all 84", and if I want to keep the tips somewhat stiffer (for say the last six inches),  I just make the bow fit the ellipse only for the inner 58"

the 1.2 factor was chosen for a slightly stiff handled bow that can be seen here

 http://www.primitivearcher.com/smf/index.php/topic,59758.msg830731.html#msg830731

of course for a fuller compass type tiller, the ratio should be increased to get further away from the rapidly changing radius at the ends of the ellipse.

fitting a bow to an ellipse and fitting an ellipse to an already tillered bow is two different things, and I agree with Del that if you are selecting ellipses to overlay a pic of a drawn bow, there are a multiplicity of ellipses that have a chord that will match.