Auxiliary Margin
Selvedge trim margins on shuttleless looms accommodate auxiliary warp ends that secure the weft before the cutting mechanism engages. Incorporating a calculated catch cord allowance ensures that the auxiliary yarns can hold the weft securely without interfering with the fabric body. This boundary is measured from the outermost fabric edge to the waste selvedge.
Edge Security
Temple actions during weaving force the fabric outward, requiring the auxiliary ends to bear high lateral stress. A generous catch cord allowance helps absorb this tension, preventing the weft from pulling back into the fabric before the tucking or binding is finished. If the margin is too narrow, the fabric edges can fray during subsequent wet processing.
Yarn Selection
Coarser yarns are usually stronger and cheaper than the warp yarns used in the main fabric body. Using the catch cord allowance, weavers can run texturized polyester or coarse cotton ends that provide excellent friction to grip the weft picks.
Waste Extraction
A cut selvedge is routed away from the fabric during the weaving cycle to a waste collection bin. An improper catch cord allowance can lead to the waste strip curling and getting caught in the cutting blades, which halts the loom.
