Grading and shrinkage allowance errors on a boys' school shorts order
A Panipat unit has an order for 1,800 boys' school shorts in cotton twill for a Haryana school chain, in sizes 22–34 (seven sizes), to be delivered before the June session. The fabric supplier's wash test shows warp shrinkage of 4.0% and weft shrinkage of 2.0% after three home washes. The patterns were graded with a constant 4 cm waist increment and a 3 cm length increment for every size, and the waistband is a straight rectangle graded only in length. Cutting lays 40 plies on 110 cm fabric, and the marker runs at 76% efficiency. After the first delivery the school reports that size 22 fits well but size 34 is tight at the waist and short in the leg, and 8% of pieces show twisted side seams after washing. The buyer wants a repeat of 2,000 pieces in three weeks and has asked for the grading to be 'rechecked'.
1. Explain why size 34 is tight and short even though the patterns were graded, and propose corrected grade rules.
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Two different faults are being reported as one. Tight waist is a grading fault. Children's waists do not grow linearly across the size range; the step between sizes 22 and 34 works out at roughly 5 cm per size step in a standard chart, not 4 cm. Six steps at 4 cm leave size 34 about 6 cm small at the waist, which matches 'size 22 fits, size 34 is tight'. The seat and crotch curve must be re-proportioned as the size rises, not just offset. Short leg is a shrinkage fault, not a grading fault. A 3 cm length increment is generous, so if the leg is short after washing, the cut length never carried a shrinkage allowance. Correct approach: rebuild the grade rules from the buyer's measurement chart with size-specific increments, check the crotch curve at each size on a nest, and apply the shrinkage allowance separately to the cut pattern, never by tweaking the grade.
2. Calculate the shrinkage allowance you would apply to the cut patterns, and explain why simply adding 4% to the length is not exact.
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The allowance must be applied to the cut length so that the finished length is correct after washing: cut length = finished length ÷ (1 − S). For warp at 4.0%: divide by 0.96, i.e. multiply by 1.0417 (add 4.17%). For weft at 2.0%: divide by 0.98, i.e. multiply by 1.0204 (add 2.04%). If you simply add 4% to the pattern, the washed result is 1.04 × 0.96 = 0.9984 of target - short by about 0.16%, small at 4% but growing quickly at higher shrinkages (at 10% the error is a full 1%). Since the twill shrinks differently in warp and weft, apply the two allowances separately along length and width, and do not forget the waistband and pocket pieces. Confirm the figures with a three-piece cut-and-wash test from the actual bulk roll before releasing the lay.
3. Identify cutting-room actions to improve marker efficiency and reduce side-seam twisting.
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Marker efficiency: 76% is low for shorts, which normally run 82–88%. Combine sizes in a marker that matches the order ratio instead of cutting size-by-size, reduce end allowances, and place small parts such as pockets, fly pieces and waistbands in the gaps, respecting grain tolerance. Check whether the 110 cm width is being used fully; a marker made for 112 cm fabric on 110 cm cloth wastes a strip down the full lay. Twisting: 8% after washing usually means the fabric was spread off-grain or was not relaxed. Let rolls relax at least 24 hours in the cutting room, check that the weft is square to the selvedge before each lay, align both ends of the lay to the same line, and reduce ply height where the twill is spongy. Off-grain cutting plus 4% warp shrinkage is exactly the combination that pulls side seams into a twist.