Bowmen of Skelmersdale

Causes of Bow Vibration

The archer

Most people depend on one particular vibration - your heartbeat - to stay alive.

Thats at about 1Hz, sitting still. Further up the frequency range are oscillations caused by poor bow control at around 2 to 10 Hz (related to typical reaction time) then muscular tremor at perhaps 10 to 30 Hz.

Limbs

Slight imbalance in the limbs will result, after the shot, in visible asymmetric limb vibration (ie as the top limb moves forwards, the bottom limb moves back, so the nocking point moves up and down rapidly) (see diagrams below). This movement produces a frequency around 10-20 Hz depending mostly on bow weight and limb material and mass. Notice that this natural frequency for the

limb vibration is not far from some of the archer s movement frequencies, and as the bow is drawn, the natural frequency drops.

String

The string has a natural frequency in the range of a few hundred Hertz when near rest. It is set in motion by the shot.

Riser

Shooting the bow causes a lot of flexion in the limbs and riser as the limbs reach the limit of movement imposed by the string. The shock starts a whole set of different vibrations off, mostly at high frequencies.


Asymmetric Vibration

Symmetric Vibration

What bow behaviour needs controlling?

Bow  movement

Timing - When is movement important?

Time and Motion

Controlling bow displacement

Weight, Mass and Inertia

Static and Dynamic properties

The misnamed TFC

Controlling bow balance

Centre of Gravity

Finding the centre of gravity

Changing the balance using weight

Weights and Distances

Rods, weights and risers

Controlling bow vibration

Causes of Bow Vibration

Reducing Vibration - Damping

Bow Resonance

Tuned damping - more on TFC’s