Too circular??

[Del the cat]

Just to clarify my position in this excellent discussion.
It's self evident that you could get any shape tiller by tapering either thickness or depth and leaving the other parallell.
That's all I'm basically trying to say!
The best tillered bow will doubtless have a combination of the two and to try to put it all down to front profile seems an oversimplification.
I've heard the classic Holmgaard tiller shape being held up as an example of tiller reflecting front profile... but it doesn't! The levers are only stiff because they are thicker not because they are narrow and parallell! Without the thick tlevers it would be very whip tillered (or snap!)
Del

[Pappy]

Looks very good to me.
   Pappy

[k-hat]

Thanks Pappy

I hear ya Del, i didn't understand you to be saying otherwise.  I've only made two pyramid bows (and one bendy bow), both pyramids came out "rough" with about as even thickness as is possible (both boards).  The tiller process resulted in both having a very slight thickness taper most of the length (guessing maybe 1/16-1/32"). 

Henry:  I don't think tapering width and thickness is a mistake at all, unless you taper one of them too much!  It seems to all go back to what do you want out of the stick.

[SLIMBOB]

Del.  Your right.  You can get any tiller shape with any front view profile.  The question I ask is, which tiller shape will give me the best possible performance with a particular front profile.  I think what's getting overlooked here, is that initially this bow was 68" in length (I'm assuming it's the same bow).  Early on when he was first tillering the bow, maybe had it drawn to 12 inches or so, he asked how the tiller was looking.  I and a few others said that at 68" with parallel limbs, he should shoot for a more elliptical tiller.  I believe that was good advice based on the bows parameters.  At 68 inches and parallel limbs (assuming a 28" draw), when the bow is bending close to the handle, you are spending stored energy throwing a lot of wood forward.  Add to that, a dense heavy wood.  If the bend begins farther from the handle (elliptical), you are spending less energy because you are moving effectively, shorter limbs which are liter.  The bows length and dense wood allows, or maybe suggests you do this.  The bow ended up being 60 inches.  That changes the equation a bit.  You now have to get the wood close to the fades working to even out the strain, and you are working with shorter liter limbs to boot.  I think a slight width taper from handle to mid limb on this bow MIGHT add a bump in performance for the reasons discussed, but we really start to split hairs.  It's an academic debate.  Interesting none the less.     

[Tom Leemans]

Your design dictates the shape of the tiller. Beyond that, when both limbs work evenly and the stresses are distributed evenly along the length of the limb (get out the tillering gizmo!) and you are at the draw length and weight you want, you're there!

[k-hat]

Same bow Slimbob, cept i was mistaken about the length.  It started out at 64" ntn, then yes i piked it to 60" ntn.  It went from 28" limbs to 26" limbs.  Saw half-eye's creations and was a hair under the goal weight, so I said why not shorten her up and speed her up.  She's elm and tempered and can handle it.  Who wants to play it safe anyway?    I was actually thinking of trimming the width a little as you mentioned, mainly looking at mass characteristics, i've got a little weight to lose.

To me there's not much disagreement here.  I sure appreciate y'all discussing this, I didn't realize I was gonna learn (and re-learn) that much from a "simple" question   I feel like i've definitely graduated to another level in understanding performance design characteristics.  I can't imagine how long it would've taken me to get to this level of understanding on my own!!!

[mikekeswick]

How thick a particular piece of wood is will determine how far it can bend without taking set.
Thats the long and short of bow making.
When you have some taper in thickness you SHOULD have an elliptical tiller. If your tiller is circular then the inner limb is being over strained and this will be shown by that area having taken more set than it should have.
Sure you can make your limbs bend into whatever tiller shape you want but the wood will let you know when you've done it wrong!

[Del the cat]

How thick a particular piece of wood is will determine how far it can bend without taking set.
Thats the long and short of bow making.
When you have some taper in thickness you SHOULD have an elliptical tiller. If your tiller is circular then the inner limb is being over strained and this will be shown by that area having taken more set than it should have.
Sure you can make your limbs bend into whatever tiller shape you want but the wood will let you know when you've done it wrong!

Ah Mike.
Indeed I can't argue with what you say, and to some extent I think we are arguing over how many angels can fit on the head of a pin.

The problem I have is that for every effect or rule of thumb there is an opposing word of wisdom. E.G  people say in one breath 'You want eliptical tiller', but the next 'The Holmgaard design is one of the best', which does the opposite (putting all the bend in-board).
As I see it, it's about compromise, and I'm not saying eliptical tiller isn't the best.
I'm just saying it isn't necessarilly achieved by the front profile.

As a simplified example:-
You could tiller a bow to 90% draw with parallell limbs by tillering thickness only. You'd look at it and say, blimey it has all this excess weight at the ends and we all know the thickness contributes more to stiffness than width, also there is V little leverage at the tip. So I'll reduce the width of the tips until I just see the tiller/draw weight shifting.
Thus the front profile is determined by the tiller not t'other way round!
Hang on I've just realised I'm discuss ing gnat excrement and it doesn't really matter if A causes B or B causes A.
Del
 

[mikekeswick]

Well holmgaard style bows are well made then they should have a mildly elliptical tiller definately not having 'all the bend inboard'. The width on the holmgaard bow is widest at the fades and has a slow width taper which then 'steps in' out to the tip. This means that there will be a width taper which also means that the bend should increase out to where the 'shoulder' is. If you make it bend straight out of the handle then you are losing a lot of potential.
You say that having a parrallel width bow will give excess weight out at the ends...well not if it's bending correctly there. I've made bows that are parallel width until 8 inches from the nocks and they have shot 170fps plus which would indicate that there is no excess weight hanging about doing nothing! If it's bending close to it's limit then it isn't surplus to requirements.
I still stand by the thickness of the wood dictating how much bend it can take without inducing set.
Here are a few bows that correspond to the front view dictating tiller principle.
http://paleoplanet69529.yuku.com/topic/45302

[Del the cat]

Mike! I shall have to give up trying to agree with you!
 
Maybe it's just semantics.
I'd say front profile is 'reflected' in the tiller rather than 'determines' it.
'Determines' is just a bit too strong a word to me. Maybe I'm just a pedant.
Del

[SLIMBOB]

Checked the PP link out Mike.  Awesome bows.  Love the BL bow.  All three very sweet. 
Del, welcome to the dark side!

[k-hat]

Mike i think what you missed in Del's example was "parallel limbs by tillering thickness only".  If you considered your example in light of Del's, you're both getting the same end result, just from different methods.  I take my daughter to camp every summer down in Austin.  We have friends who take theirs as well.  I go the major highways, he goes the backroads, but we both get there

I kinda like the statement "front profile is affected by tiller" (or would that be effected?!?).  Seems like a good idea to keep both perspectives in mind.
In fact, Del i think i'll try that on one of my next bows just to experiment.  It would be interesting to take two "identical" staves and work one by tillering thickness, then narrow the tips, and do the other by cutting the front profile and initial thickness taper, then tiller the final thickness, and see how each turns out.  Which one is more likely to end up on target?

[soy]

Mike i think what you missed in Del's example was "parallel limbs by tillering thickness only".  If you considered your example in light of Del's, you're both getting the same end result, just from different methods.  I take my daughter to camp every summer down in Austin.  We have friends who take theirs as well.  I go the major highways, he goes the backroads, but we both get there

I kinda like the statement "front profile is affected by tiller" (or would that be effected?!?).  Seems like a good idea to keep both perspectives in mind.
In fact, Del i think i'll try that on one of my next bows just to experiment.  It would be interesting to take two "identical" staves and work one by tillering thickness, then narrow the tips, and do the other by cutting the front profile and initial thickness taper, then tiller the final thickness, and see how each turns out.  Which one is more likely to end up on target?
  that sounds like the mother of invention ...i cant wait to see that build along!