knockoff

A knockoff is a mechanical device mounted on a knitting machine that strips completed loops from the needle beds and advances the knitted fabric toward collection. It operates by pushing finished stitches over the needle tips, breaking the loop connection and allowing the fabric to descend. On circular knitting machines, the knockoff typically consists of a rotating or reciprocating cam-driven assembly positioned above or around the needle cylinder. On flat-bed machines, it may be a fixed or moving rail that clears needles systematically across the width of the bed.

The knockoff sits downstream of the needle zone in the machine's hierarchy. New yarn is fed to needles, stitches form on the needle shafts, and once a loop has been knitted to the required number of courses (rows), the knockoff engages and removes it. Without a knockoff, fabric would simply accumulate on the needles and jam the machine. The device is essential to continuous or semi-continuous operation, whether the machine produces hosiery, warp-knit fabric, or weft-knit goods.

Variants and Mechanical Detail

Circular machines typically use rotating knockoff arms or a cam-driven ring that lifts and rotates to strip loops. Flat-bed machines employ a rail or bar that moves across the needles, often with spring-loaded or pneumatic actuation. Some machines use multiple knockoff stages for thick or heavy fabrics. The knockoff must apply enough force to separate the loop from the needle without snagging, splitting, or laddering the yarn. Timing is critical: if it engages too early, incomplete stitches drop; too late, needles jam.

Common faults in knockoff systems include worn cams or rails that fail to fully clear all needles, leading to dropped stitches or incomplete rows. Needle latch failures also reduce knockoff effectiveness because loops may not sit properly for removal. Springs and dampers in the mechanism can fatigue, causing erratic or weak ejection. Lint and fiber buildup around the knockoff zone increases friction and can cause stalling.

The term 'knockoff' derives from the action of knocking loops off the needles. It is distinct from cast-off, which typically refers to the final closure of loops at the edge of a piece of finished garment, and from take-down or let-off, which manage tension and advance the fabric through the machine. Knockoff systems vary widely between machine manufacturers and are usually one of the first items a knitting technician learns to troubleshoot when production quality drops.