REALLY tiller on the edges?

[Knoll]

I've made a few bows from boards.  All relatively narrow (ala 1 3/4 or less) with various width tapers ... beginning at fades, 4" from fades, and some as much as 12" from tips.   And usually constant thickness.  I've tillered all of them by reducing wood from belly.  Never from edges.

Now I'm about to begin tillering my widest-limbed bow ... 2 1/4".  Width is constant to 4 1/2" beyond fades.  Then tapering to 1/2" tips.  Thickness is constant too.

I've come to understand that pyramid-tapered limbs should be tillered by removing wood from edges, not from belly.  While my past approach of removing wood from belly has resulted in shootable bows ... how truly good they are I don't have enough experience or chrony to judge.

Since this bow is so wide, I'm thinking maybe I should tiller this one by removing wood from edges.
     What are the advantages of doing so? 
     Use a rasp in beginning stage, then scrap, & then sand?  Constantly re-rounding edges?

This bow will be a new adventure .......

[bubby]

I'm not sure where you got the Info on side tillering pyramid bows, I've built a ton of them and don't think I've ever side tillered one, I start with an even thickness but buy the time I'm done tillering there's usually a silght thickness taper

[George Tsoukalas]

Tillering from the edges is possible with a wide limb...say around 3 ". Never done it though.

I've tillered log staves from the edges when they don't respond to belly wood removal.

I've tillered narrow (2 in) pyramid shaped limbs from the belly.

There's no hard and fast rule. IMHO.

Jawge

[PatM]

It really depends if you subscribe to the front shape matching tiller shape mantra.
 I don't. Wood is not that smart.

[bradsmith2010]

if you have the bow tillered well and want to reduce the weight,, from the side is good,,

[DavidV]

if you have the bow tillered well and want to reduce the weight,, from the side is good,,

Exactly. It's easier to scrape 1/2" evenly than 2 inches.

[Jim Davis]

A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.

The whole purpose of a "pyramid" design is to have the whole limb at the optimum thickness for the amount of bend desired.

Then, the whole length of the limb, the width is appropriate for the weight desired. A straight taper accomplishes this--with one necessary modification. Ideally, the taper would form an apex at the tip of the limb. But the tip needs to be big enough to hold the string. So, the limb should be tapered only to where the sides are about a half inch apart. From there, the last few inches of the limb should be parallel to the tip.

With that design, the limb will be perfectly or almost perfectly tillered right off  the saw. If not,  narrow the limbs where needed.

[Knoll]

A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.

Thanks for pulling the quote.

So, an optimum pyramid design is one where width taper and thickness is so close to ideal (given weight/pull objective) that little tillering is needed.  Much the same could be said for any design ... that limbs are sized so close to optimum that little tillering is needed.

For a 50#/28" pull bow I guessed at 2 1/4" tapering to 1/2" and thickness of 15/32".  Not surprisingly, those dimensions yield limbs too stiff for the objective.  So, according to Jim Davis, limb width is where wood should be removed.  Correct?

[Danzn Bar]

What kind of wood we talking about ... osage, mulberry, hickory or ash....it all makes a difference to limb thickness, related to width.
DBar

[Jim Davis]

Yes it does matter what kind of wood. But there is one thickness for each wood in a "pyramid" design that is right for each length of limb/draw length combination. There is no number that can be attached to any of these situations, but there is aright thickness.

A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.

Thanks for pulling the quote.

So, an optimum pyramid design is one where width taper and thickness is so close to ideal (given weight/pull objective) that little tillering is needed.  Much the same could be said for any design ... that limbs are sized so close to optimum that little tillering is needed.

For a 50#/28" pull bow I guessed at 2 1/4" tapering to 1/2" and thickness of 15/32".  Not surprisingly, those dimensions yield limbs too stiff for the objective.  So, according to Jim Davis, limb width is where wood should be removed.  Correct?

Thickness that is right for the amount of bend takes into account the length of the limb. As for your example, no, if your bow is around 66" ntn, the limbs are plenty thin enough to bend without taking set. The bow has more width than you need if it is too stiff. It should be narrowed in straight lines--the fades should be narrower but the nocks should be left as is.

Lots of us have found these things to work in practice (for at least the last 75 years) and the math of physics bears it out.

I did not discover any of these ideas or practices. I just do them. There is no reason for me to defend  them, I had only hoped to explain them. A foolish goal, perhaps.

[Danzn Bar]

Yes it does matter what kind of wood. But there is one thickness for each wood in a "pyramid" design that is right for each length of limb/draw length combination. There is no number that can be attached to any of these situations, but there is aright thickness.

Agree 100% Jim    But everyone was talking a lot of dimensions...
DBar

[Knoll]

So, Jim, if wood is removed from edges, roughly how much would recommend to remove before putting the bow back on tillering tree to see where you're at with weight/pull/bend... particularly during early tillering when ya know good bit needs to be removed, but don't want to "over do it"?

[Jim Davis]

So, Jim, if wood is removed from edges, roughly how much would recommend to remove before putting the bow back on tillering tree to see where you're at with weight/pull/bend... particularly during early tillering when ya know good bit needs to be removed, but don't want to "over do it"?

If your limbs are of even thickness from fade to tip and the sides are a straight taper, you can figure out exactly how much narrower to make the limbs to reduce the draw weight to what you want.

If the bow pulls 50# and you want 40#, the width needs to be 4/5ths of what it is now. If it's 2-1/2" wide at the fades, it needs to be 2" wide to pull 40#. Leave the tip width or the width where the tip becomes parallel unchanged.

The bend will stay the same curvature no matter how wide or narrow the taper, barring any change in relative stiffness by the loss of local relatively stiffer or weaker wood. That is, if the wood is of uniform stiffness from fade to tip, the curvature will not change by narrowing the triangle.

[mikekeswick]

Asharrow has nailed it on the head!

[mikekeswick]

It really depends if you subscribe to the front shape matching tiller shape mantra.
 I don't. Wood is not that smart.

EH?
It's not about wood being smart it's basic physics. Wood certainly isn't smart enough to think itself above and beyond the laws of physics! Thicker material won't bend as far as thinner material - simple. A constant thickness limb should be bending the same amount along it's length.