Bowmen of Skelmersdale

Reducing Bow Vibration ‘Damping’

In principle, vibration will continue until stopped. A vibrational movement which is being reduced by some external force is said to be damped . Very often, the time vibrations take to stop is too long, so engineers spend a lot of effort in inventing methods of controlling or slowing vibration more quickly. The basic principle of all these methods is to provide a method of transferring energy away from the vibrating

object and into some system that dissipates the energy without adding more vibration. Some common examples include:

Friction.

Any friction slows vibration by dissipating energy as heat. Frictional force is constant, so the final resting point of the object is slightly uncertain. Powder filled stabilisers use the friction between powder particles to dissipate energy.

Fluid, or viscous , damping.

Movement through a fluid needs a force proportional to speed of movement, making fluid damping very useful when an object is to be brought progressively to a known rest point. A piston or weight moving through oil transfers energy to the oil, which dissipates the energy as heat. Most of the energy is lost in overcoming fluid viscosity (or thickness), hence the alternative term.

Hysteresis effects.

When you stretch and squash a material like rubber, you store energy in the material. Each time you let the rubber return to rest, much of the energy comes back in the form of movement. But some is lost and, as usual, turns up as heat in the rubber, so you can t just let go and let the material keep oscillating. Systems which move from one state to another and exactly back to the first with loss of energy at each cycle (as the rubber moves from squashed to stretched and back to squashed) are exhibiting hysteresis . The effect is used in TFC rubber to damp oscillation. Some manufacturers even sell special high hysteresis rubber parts to improve damping.

Structural effects

Some materials, particularly composites like carbon fibre, soft foam rubber and wood, absorb energy well through combinations of the effects above. So Carbon rods tend to absorb high-frequency, post-shot vibration more effectively than aluminium rods

All these methods rely on one essential fact. To damp movement, the movement must be transferred quickly and effectively to the damping device. To make this happen with vibrational movement, we often need to think about resonance.


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