Drafting
Also searched as: draft, drawing, draw ratio, roller drafting, draft ratio, attenuation, gilling
Drafting attenuates a fiber strand by making fibers slide past one another, usually between pairs of rollers running at increasing surface speeds, so the strand becomes longer and finer.
In detail
A drafting zone grips the strand at two nips. The front, or delivery, rollers turn faster than the back, or feed, rollers, so each fiber released by the back nip is accelerated as soon as the front nip catches it. Drafting happens on drawframes, roving frames and ring frames, and on worsted gill boxes, where pinned fallers control fibers between the rollers. At the drawframe several slivers are fed together (doubling) while being drafted, which averages out irregularities; drafting also straightens fibers and aligns them with the strand axis.
The science and numbers
Draft is the ratio of delivery surface speed to feed surface speed and, ignoring waste, equals input linear density divided by output linear density. Total draft over several zones is the product of the zone drafts. In cotton spinning drafting systems, the back-zone break draft is usually about 1.1 to 1.5 and the front-zone main draft about 6 to 30. Aprons in the main zone guide fibers too short to span the nip distance. Nip spacing is set somewhat longer than the longest fibers, so no fiber is gripped by both nips at once, which would break it or make it slip erratically. On drawframes, a tension draft of slightly less than one is used between delivery and feed points to keep slivers taut without drafting them.
A practical example
A drawframe is fed six slivers of 5 ktex each, 30 ktex in total, and delivers one sliver of 5 ktex. The total draft is therefore 6, matching the ratio of delivery to feed roller surface speeds. The output is no finer than any single input sliver, but blending six sources into one makes it noticeably more even.
What to distinguish
Drafting is not twisting; twist is added afterward, or on a roving frame in the same machine, to consolidate the drafted strand. A higher draft is not automatically better, because fibers held by neither nip, called floating fibers, move irregularly and create thick and thin places. The spacing between nips relative to fiber length matters as much as the draft figure itself.
Origins and history
Roller drafting was the central idea of the mechanized spinning machines of eighteenth-century England, replacing the hand spinner's fingers that drew fibers out of a distaff or rolag. The older English verb 'draw' survives in the names drawframe and drawing, while mill technicians use 'draft' for the numerical ratio of speeds. Wool worsted systems developed the pinned gill box to control long fibers during the same operation.
Related terms
Sources & further reading
- ScienceDirect Topics: Roller drafting
- Woolwise (University of New England): Drafting and gilling of fibrous assemblies
- Textile Learner: Draft, draft constant and production calculation of drawframe
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.