#2
Post
by Dennis La Varenne » Fri Oct 22, 2010 12:43 am
Andy,
It is pretty hard to judge the quality of the tiller in a picture of a drawn bow, but here is how I do it. I downloaded your picture and opened it in Photoshop. I then draw a line from string nock to the end of the riser. Then I compare the area under the limbs and above the line. Because it is difficult to see in your original picture, I have overdrawn the upper limb for clarity.
You can see in this redrawn picture that there appears to be a greater gap between the lower limb and the line than in the upper limb. This may indicate either of two things -
Firstly, that you have tillered the bow with too weak a lower limb, or
Secondly and the more likely from looking at this picture, that the shooter is 'heeling' the bow and causing the lower limb to 'belly' out a bit.
Heeling is the term used when too much pressure is being put against the grip of the bow by the lower part of the bow hand. On a recurved bow, the drawing pressure should come against the web of the bowhand or at worst no lower than the thenar prominence (ball of the thumb) so the bow is in balance when drawn.
Being in balance when drawn means that there is equal bending of the limbs at full draw which indicates that there is equal drawing force on each limb and therefore they will accelerate at the same speed to drive the arrow. The stored energy in the bent limbs will be applied to the arrow most efficiently that way. If there is more pressure against one limb compared to its mate, then they will accelerate at different speeds and the stored energy from the limb with the greatest bend will do most of the pushing and the slower limb will come to a stop fractionally later than the other resulting in some recoil in the bow limbs felt as vibration after the arrow has left the bow.
This may or may not be happening. It is a matter of degree of difference in the amount of bend between each limb. But, I would suggest from your picture that you try to get the young bloke in the picture to try lifting his lower hand a bit more off the grip and taking the pressure more into the web of his bow hand, THEN have a look at the tiller. If he is not sure about the security of his grip, get him to wrap only his thumb and index finger aroung the throat of the grip and open the rest of his fingers. This will bring the drawing pressure against the correct part of his bowhand for a recurved bow. This type of grip is called a 'high wrist' grip.
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Dennis La Varénne
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