Pyramid vs Elliptical

[sapling bowyer]

Hi guys I want to know the pros and cons of two kinds of designs. The pyramid taper and the elliptical taper( the kind that the limbs are parallel until about 2/3 of the limb when it tapers down in the last 1/3) The wood I want to use is hazel and it will be around 55-60 inches in length. I'm stuck with choosing design and I want to know more about these designs. I'm planning on 40#@23". Also do I have to make a thickness taper if I use the elliptical design?

[wizardgoat]

Pyramid and parallel are in relation to your limb profile, and circular and elliptical are tiller shapes.
A tapered profile (pyramid) should be a little more circular, and parallel limbs should be a little more elliptical. Either design works just fine when they are executed right.
Both designs you will have to remove wood to make it bend right, so yes, there is a thickness taper with pyramid limb bows, just maybe not as much with parallel limbs

[willie]

A tapered profile (pyramid) should be a little more circular, and parallel limbs should be a little more elliptical.

Wiz

I have never understood why this advice is often put forward, could you share more?

I do realize that a pyramid back profile could be tillered elliptical, and parallel back tillered to circular (isn't that the prefered tiller for an elb?), and with proper tillering,the difference might be small, but why the preference?

thanks
willie

[joachimM]

Those tiller shapes relate to stressing the wood all over the bow the same amount. This ensures that all the mass is doing its fair share of work.
Thicker wood can store more energy, but cannot bend as much before taking set. So parallel inner limbs will have more thickness profile than pyramid inner limbs. The thicker inner part cannot bend as much, so the tiller shape is more elliptical. In a pyramid bow, it is possible to have no thickness taper from fades to tip whatsoever. that results in a (nearly) circular tiller.

On the paleoplanet forum this was discussed some ten years ago: http://paleoplanet69529.yuku.com/topic/11187/Pyramid-Bows-and-Thickness-Tapering#.VrOrE4XhBD8

Joachim

[sapling bowyer]

Thanks guys but I have one more question. Does the tiller shape: circular or elliptical affect the performance of the bow. I just read some stuff about this in the tbb vol 4 but because I am not native in english I could not understand fully.

[loon]

I think elliptical stores less energy but can be faster if outer limbs would otherwise be too heavy, less handshock with lighter/medium weight arrows

Circular stores more energy than elliptical if elliptical is more "whip tillered" than circular. But can have handshock if outer limbs aren't narrow/light enough.

[bradsmith2010]

my understanding is that if done properly,, they both can give great performance
the tiller has to match the front view profile,,
wide to thin,, more circular,,
parallel,, more elliptical,,

if you try to make a pyramid bow with elliptical tiller it won't work well, it will be whip tillered and won't stress the limb evenly, taking set in the wrong places

if you try to make a parallel limb ,, circular,, it will take too much set at the fades and have too much mass in the outer limbs and not shoot well or break,,

its hard to explain,, it is about a whole chapter in a book,,

[joachimM]

Bradsmith, I think you nailed it there.

[willie]

that was an interesting discussion in the link Joachim provided. Baker did point out that properly locating the highest stressed part of the limb, puts the desired set i all the right places.

[George Tsoukalas]

Bows with nearly parallel limbs can be tillered elliptically.

Pyramid bows should appear more rounded. As Brad suggests, wider, near handle wood can and should bend more tha narrow near parts near the nock. Thus the tiller appears more rounded.

I see no advantage of one over the other.

Jawge

[sapling bowyer]

I guess that the pyramid design would perform better because it would have less mass at the limbs than elliptical if they both start at the same width and taper to the same width. Also the pyramid bow would be easier to tiller.

[PatM]

Make them, don't guess.

[George Tsoukalas]

sapling bowyer, it is usually the last 8 inches that count and that area can be taperd on a bow with parallel limbs.
The anger, as Brad said, with pyramid bows is they are made whippy.
Agreed that they can be easier to tiller as long as the tiller becomes circular.
Jawge