Twill Sett and Shrinkage on a 4-Shaft Table Loom
A vocational student is weaving a 2/2 twill scarf on a 4-shaft table loom with a 40 cm weaving width. The warp is 2/20s cotton (two-fold, 20s count) and the plan is 18 ends/cm and 14 picks/cm. The available reed has 6 dents/cm, and the student plans 3 ends per dent. The warp length on the beam is 3.2 m; the required finished length is 2.2 m. After 40 cm of weaving, the cloth measures 36.5 cm wide and the picks/cm is 15.2. The selvedges are drawn in, and two warp ends near the right selvedge have broken repeatedly. The student wants to correct the width by pulling the weft tighter and beating harder.
1. Check whether the sett is correct and calculate the number of ends, the denting, and the required warp length allowing 12% take-up and 8% shrinkage.
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Sett check. Ends = 40 cm × 18 ends/cm = 720. At 6 dents/cm and 3 ends/dent, 720 ÷ 3 = 240 dents; 240 ÷ 6 = 40 cm. The denting is correct for 18 ends/cm, so the sett itself is not the cause of the 36.5 cm width.
Warp length. Required finished length 2.2 m. Allow 12% take-up and 8% shrinkage: 2.2 × 1.12 × 1.08 = 2.66 m. Add 0.4 m loom waste = 3.06 m; the 3.2 m beam is adequate but not generous.
Diagnosis. A 3.5 cm loss (8.75%) with ppi rising to 15.2 suggests excessive weft tension and/or hard beating, causing draw-in. Check warp tension across the width, fit a temple, reduce beating force, and set weft tension so the weft lays in without pulling the selvedges. Measure after relaxation, not on the loom.
2. The student wants to change to a 3/1 twill for a stronger diagonal. Explain the threading, tie-up and treadling changes and the effect on float length and sett.
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3/1 twill change. Thread straight 1-2-3-4. Tie up so each treadle lifts three shafts: treadle 1 lifts 1-2-3; treadle 2 lifts 2-3-4; treadle 3 lifts 3-4-1; treadle 4 lifts 4-1-2. Treadle in order 1-2-3-4 for a right-hand diagonal; reverse for left-hand.
Effect. The float length becomes 3, not 2, so the cloth is warp-faced, firmer in the warp direction but more prone to snagging on the back and less balanced. For a scarf, 2/2 is usually better. If using 3/1, increase ppi slightly or reduce ends/cm to keep cover balanced, and test drape and abrasion. The sett may need re-sleying; do not simply change the tie-up and expect the same width.
3. Evaluate the proposal to fix width by tightening weft and beating harder. Give a corrective plan.
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Reject the fix. Tightening the weft and beating harder increases draw-in and ppi, making the cloth narrower, not wider.
Corrective plan. (1) Check warp tension end-to-end and side-to-side; correct loose or tight sections. (2) Fit a temple of the correct width. (3) Set weft tension and shuttle timing so the weft is laid straight; use a lighter beat. (4) Inspect the right selvedge heddles and reed for burrs; replace damaged heddles and check the shuttle path. (5) Weave a 20 cm sample, relax it, and measure width and ppi. If 40 cm is mandatory, re-sley to about 19 ends/cm and allow 5–8% shrinkage. Record the corrected reed plan.