beater
A weaving tool designed to push the weft yarn securely into place. It contains the comb-like insert reed and is sometimes a part of the loom.
beater: the loom's hammer that locks in every pick
The beater is the swinging frame assembly mounted on a loom that drives the weft yarn firmly against the fell (the line where new cloth is being formed). It pivots on a horizontal shaft called the race and swings forward with each pick cycle, compressing newly laid weft threads into the cloth body. Without a beater, the weft would sit loose and the fabric would be weak and open.
The reed, a comb-like set of parallel wires or thin strips, is the working edge of the beater. Reed spacing is measured in dents per inch, typically ranging from 4 to 30 or more depending on yarn fineness and cloth type. A loom designed for fine fabric might use a 24-dent reed, while heavy tapestry might use only 6 dents. The reed sits in a groove on the beater frame and can usually be removed and replaced.
The beater's timing and force are critical to weave quality. On a traditional shuttle loom, the beater strikes immediately after the shuttle passes through the shed, while the warp threads are still separated. On modern projectile and airjet looms, the beater may pulse multiple times per pick cycle. If the beater strikes too softly, the cloth becomes spongy and loose; too hard, and warp threads may break or crimp unevenly. Mechanical wear on the race journals can cause the beater to swing at inconsistent angles, creating visible density variations in the cloth.
The name derives from the beater's primary action: it literally beats the yarn into place. In some older texts and regional usage, the entire assembly is called the lay, though lay can also refer just to the reed holder. The German term is Schlag, which has the same root sense.
Beater design varies significantly across loom types. Rigid-heddle looms use a simple hand-operated beater that the weaver moves manually. Power looms have cam-driven or linkage-driven beaters synchronized to the timing of the shed opening and shuttle or projectile launch. Air-jet looms often have lighter, faster beaters because the projectiles deliver weft at higher speeds. The mass and angle of the beater frame affect both the force profile and the mechanical load on the loom's main structure.