asymmetry in hornbows

Uli · Post by **Uli** » Thu Oct 26, 2006 9:31 pm

Dear ATARN members,

I d like to ask a question on hornbows:

I noted that the hornbows I got to shoot were all designed slightly asymmetric, ie when braced, one limb (the upper) bends more than the other. but if one draws the bow, this asymmetry usually disappears
(provided one uses the bow with the more bending limb as upper limb).

Is this a wanted effect, and if so, based on which reason ?

thanks for your replies

Bede · Post by **Bede** » Thu Oct 26, 2006 10:14 pm

Do you mean horn, wood and sinew composite bows when you say horn bows?

If you do, the curve of the limbs is adjustable by the archer. You can bend the stiffer limb over your knee for a minute or so to correct the curve. Usually the bow holds the new shape for several hours.

Uli · Post by **Uli** » Fri Oct 27, 2006 7:31 am

yes, more specifically mongolian composites.
I did shoot some and one of my mongolian friends has
a bow (http://198.170.108.27/phpBB2/viewtopic.php?t=558)
like this one I also found on the internet (attached)

You can clearly appreciate the slight asymmetry, also in the ankle of the siyas, and the lower limb is 1.5cm shorter
( sorry, on my pic I the nock point is dilocated to the lower limb )

I thought this asymmetry would be unintentional but now
I thought maybe its menat to correct
the fact that whenever one draws such a bow (thumb draw,
hand in middle of handle), the lower limb tends to bend more.
( no objective mesurement, but you may try for yourself )

see pics

Uli

Stephen Selby · Post by **Stephen Selby** » Mon Oct 30, 2006 2:22 am

On your photo, BowStrung.jpg, I would prefer to adjust the limb slightly with warming and bending. Although it is correct that the bow is not completely symmetrical, it should not be as exaggerated as the photograph. Visually it should not be perceptible.

Rapsod · Post by **Rapsod** » Mon Oct 30, 2006 8:21 pm

Upper limb is longer.

Uli · Post by **Uli** » Sat Nov 18, 2006 3:08 pm

I think I found a possible answer at a site on archery mechanics..

Draw Geometry

When the bow is drawn the draw force in most cases acts between the nocking point and the bow grip (The exception is the bare bow archer who string walks). When the arrow is shot the string force is acting on a line between the nocking point and around the arrow rest position. As the arrow rest is a couple of inches above the throat of the grip this geometry change may result in a vertical nock movement effect. In effect, at full draw prior to release (assuming the springs are equal) the bottom limb is drawn more than the top limb. On release the limb springs are not balanced with respect to the arrow/string force and the nocking point moves downwards as the lower limb moves forward more than the top limb. You can offset this effect by making the lower limb stiffer than the top limb so it doesn't move as much. Compensation for this effect is usually built into the bow design.

The Archer

Nocking point tuning includes the effects of how the archer holds and releases the bow string whatever the finger pressure balance the archer uses. Variations in the loose will introduce variations in vertical nock movement, particularly if the 'final' pressure point varies between being below and above the nock. The action of the bow hand can also effect the tiller (one of the effects that comes under the catch all of 'bow hand torque'). If say the archer 'heels' the bowhand then one effect is to draw the lower limb relatively more than the upper limb affecting the bow tiller. The arrow leaves the bow rotating pile upwards and the arrow ends up hitting high.