ELB tiller question(s) (related to limb length)

[Strichev]

 Now that I'm a bit better at not tearing the wood and such nonsense (survivability is no longer the primary concern) performance of a bow has become a question of importance. I'm done with pulling a 60 pound ELB only for it to have measly cast of 120 to 130 m maximum cast.

The thing is I'm not entirely sure how to tiller an ELB; as in, how do you place it on the tillering tree, where do you attach the draw rope, where on the bow is the arrow pass? The limb length thread got me to post this, as I happily clicked on it, expecting a definite answer about an optimum bow geometry. Things got even more confusing after reading it, though.


When making my first bow I supported the center of the bow and pulled at the center of the string, thereafter placing the grip below the arrows pass and thus bellow the center of the bow. It survived but it wasn't exactly pleasant to shoot, it sort of pulled (pushed?) the wrist up quite a bit (I don't know if I explained it well enough). Could this be normal for self bows? (I never shot a self bow or anything around 60 pounds before, so I don't know how it's supposed to feel on a good bow).

I've read somewhere that the arrow pass should be placed slightly above the middle of the bow. All nice and whatnot, but do you then support the bow at the arrow pass? It would seem natural to support it where the hand supports it most, thus around the middle (in a design with arrow pass above). However, does it even matter upon release?

Where do you pull it on the tree then? At the future arrow nock? Slightly below? In line with the center? Or do you make the arrow pass at the center of the bow and support it there and pull on the string in the middle too? Or do you support it below center?

Slight adjustments seem to make a visible difference in the way limbs bend.

[Dances with squirrels]

You are asking the right questions for the right reasons. These aspects of bow making are directly linked to how a bow carries, draws, shoots, how it treats the arrow and archer as a result, how easily it will be to tune, and whether or not it holds its tiller.

Here's one way to do it that I've found to work well for me... I generally design my bows so that the handle center is 3/4-7/8" below bow center. This makes the top limb 1 1/2 - 1 3/4" longer than the bottom, which allows it to balance in my hand the way I like, and keeps bow center, string fulcrum, and dynamic balance point all an inch or less from each other. This has several important benefits during and after tillering... but I digress.

The bow is placed on the tillering tree with its 4" handle centered and supported in a 4" cradle... which is level.

The string will be drawn from precisely where the center of my middle finger will be as I draw the bow, since this is my string hand fulcrum point. I find this exact spot on the wall behind my tillering tree by measuring over from the cradle(where the handle/shelf will be located) 3/8", which is where I set all of my nock points.... 3/8" above the shelf.... Then measure back from there the thickness of the arrow nock (1/4"), plus half the thickness of my middle finger (3/8"). So, this puts me at 1/4" in from the edge of the cradle (or down below the top of the handle/shelf). THIS is where I hook onto the string with my rope and pulley.... right where my middle finger will be with a 3/8" high nock point.

That point is also where I draw a vertical, plumb line on the wall for reference, from the cradle down toward the floor. This line represents the intended travel of the fulcrum point when limbs are balanced in strength relative to the string fulcrum. If they're not, the hook will drift toward the stronger acting limb as the bow is drawn, and it can be weakened as needed.

This adequately mimics how I shoot the bow, and I'm done tillering when I reach my draw length and the hook follows the line.

I give no regard to predetermined tiller measurements during the process. They are what they are when I'm done. This method balances limb strength in odd shaped bows, for example: one limb straight and the other reflexed, as well as it does those whose limbs look identical.

[wizardgoat]

DWS always has great explanations, takes a couple reads but always on point.
For me I like my bows usually 2" longer on the top limb, with a bottom limb that's about 1/4" stiffer.
I tiller my bows as you said, on the tree, handle centred, but I pull the string as DWS stated, about where my middle finger would be.
If the bow is going to 28", at about 24" and assuming the limbs are very even and brace looks very close, I no longer use the tree. I film myself and take photos, when the bow is in hand and I'm nocking an arrow, the bend will be a little different, usually stiff out the top fade.
For me I can never get a perfect tiller on the tree alone. If your bows are long and not very high weight, and shooting slow, try tillering a bow a little more elliptical instead of circular.

[Del the cat]

ELB.
Arrow pass 1" above centre.
Support the bow on the tiller tree where your hand will support the bow, pull the string from where your fingers will pull the string.
I prefer to allow the bow to rock on the tiller tree.
This post rom my blog illustrates it quite well and may be useful.
http://bowyersdiary.blogspot.co.uk/search?q=symmetry
Del

[Dances with squirrels]

Yep Del, that's the other way to do it... let it rock on the cradle. The hook still moves toward the stronger side.

[Strichev]

DWS, wizardgoat, Del, thank you all for taking the time to answer. Now it's all clear.

[Cameroo]

Hey guys, been a long time since I popped in, but I just happened to be working on a bow right now that could demonstrate how much of a difference this makes in the timing of the limbs.  I'm working on a big maple-backed yew bow that is currently tillered out to 120 lbs at 28". I have been tillering with it centered on the tree, and pulling the center of the string. This is how I've always tillered ELBs in the past, but they often seemed to look at bit "off" when drawn in the hand. This is how the tiller looks at about 21" of draw (didn't want to stress it too much for the next picture, but wanted to draw to same length for comparison):



It occurred to me that I should be pulling from where my fingers are going to be, so I shifted the hook over about 3/4" to the left on the string (arrow pass will be about 1" left of center, bow pivoting in bow hand roughly at center, and figured my middle string finger will pull roughly 3/4" left of center). This is how the tiller looks when drawn from there:



Now it looks like the EDIT:right (bottom) left (top) limb is about 2" stiffer! I guess I should probably soften it up a bit now while I still can... got about 4 inches of draw length to go yet.

[Dances with squirrels]

I think you'll like how the bow behaves if you do, Cameroo.

If you didn't already, be sure to move the pulley over the same amount as you did the hook so it's pulling straight down, not at an angle.

Is that bow symmetrical or asymmetrical?

[Cameroo]

DWS - I suppose the bow would be considered symmetrical, since the point where it pivots in the hand will be roughly in the center. In the second picture I have it set on the tree as Del described above. The shelf is rounded on top so the bow is free to pivot. No need to adjust the bottom pully since the bow adjusts itself to be drawn as it would be by hand. I think I will remove a bit of wood just right of center to bring the right limb within an inch of the left at full draw, and that should make for a pretty good tiller in the hand. It needs to bend a bit more in the center at full draw anyway, so if I do that, it should pretty much give me the last few inches of draw length that I need yet.

[Del the cat]

Confuse a cat... you have it lower limb right
I always go Lower Left
RIGHT LIMB is NOT stiffer!!!!!
Left is too stiff, it is pulling the bow down on the left. If you weaken the right limb, it will curve even more and allow the stiff left limb to pull down even harder.
Imagine the left limb is totally rigid, as you draw it the rigid left limb will cause the bow to tilt and all the flex will be in the right with it bowing upwards... I kow it's a bit counter intuitive. Maybe that's why some people like to clamp it rigid on the tiller.
Put two kids on a see saw (teeter toter?) the fat heavier kid goes down!
Del
(Scampers off to fetch mirror )

[mikekeswick]

Yep left limb is stiff From handle out to mid limb'ish.
If your bow was clamped to thte top of the tillering tree and unable to move then your right limb would be the weak one but seeing as it's free to move - left is stiff.

[Cameroo]

Ya, that's what I meant to say... I guess that's why I always tillered at the center. Keep it simple stupid! Throw something else in the mix and it all goes out the window!  Now that you point it out, it seems obvious. Good thing I didn't touch it today after I took those pics

Mike - I purposely left it stiff there because there are some gnarly knots in that section, but I think I'm at the point now where I can get it bending a bit more without an explosion.  I will attack it tomorrow!

I was honestly expecting this glue up to fail much earlier. I just pumped the knots full of CA and crossed my fingers.

[BowEd]

So if I see and understand this right.If the bow as it is was shot as in the second or lower picture it would be shooting with a negative tiller if the left limb is top limb.Material removal from left limb is needed to even it up.Then even more material removal to get a positive tiller.Now if that top or left limb was say an inch longer than it would show closer to even tiller pulled as in the second or lower picture at present stage.

[Strichev]

I guess one needs to always carefully check whether the bow is tilted on the rest or not.

Just today I faced an almost identical situation on my current bow. Just that I didn't notice right away that the bow wasn't tilted on the rest. I kept removing wood from the "stiffer" limb like advised to Cameroo. Well, luckily I noticed the situation getting worse and indeed, the other limb (the one that behaved like the right one on his picture) was quite a bit stiffer.

With something like 30 pounds to spare my mistake was far from critical.