The Complete Handbook of Compound Bows

Chapter 1: Understanding Compound Bows

A compound bow is a mechanical draw system in which the archer's muscle effort is managed by cams—rotating wheels or eccentric shapes on each limb—that increase draw difficulty initially, then substantially decrease it at full draw through a mechanical system of cables and pulleys. That reduction in holding weight is called "let-off," and it is the defining feature that separates a compound bow from a recurve or traditional longbow.

Understanding what a compound bow actually is requires understanding why this mechanical complexity exists. When a traditional archer draws a recurve bow, the draw weight—the force required to pull the bowstring back—increases continuously as the string moves away from the bow. At full draw, the archer must hold the heaviest weight. This makes aiming difficult because the archer's muscles are fatigued and shaking. A compound bow inverts this problem: the cams force the archer to work hard initially, but as the draw progresses and the cams rotate, the mechanical advantage changes. By the time the archer reaches full draw, the actual holding weight might be 60 to 80 percent less than the peak effort required. This means a hunter can hold full draw steadily for several seconds, aim carefully, and execute a clean release without muscle fatigue interfering.

This mechanical advantage comes from the way the cams and cable system are arranged. Most modern compound bows use two cams, one on each limb, connected by a cable that runs through or around them. As the archer