Four Faults on a Poly-Cotton Shirting Run Against a Shipment Date
A small garment unit in Ludhiana is running a repeat order of 1,200 poly-cotton (65/35) shirting pieces at 120 gsm. The line uses 40s/2 polyester-core-spun thread, a 14/90 needle, 12 stitches per inch and standard lockstitch machines. After the first 200 pieces the quality checker reports four faults: fine puckering along both armhole seams; skipped stitches at the collar points whenever the operator lifts the presser foot to pivot; small brown scorch-like marks and needle holes along the topstitched placket; and seam grin at the side seams when the seam is pulled by hand. The supervisor wants to slow all machines to 60% speed, which will cut daily output from 300 to 180 pieces, against a shipment date of 12 days. The buyer's specification allows a maximum 2.5 AQL for major defects and requires a seam-slippage test report with the shipment.
1. Diagnose each of the four faults, naming the most probable cause and the specific setting or component you would change.
Read the worked answer
1. Puckering along the armhole seam
- Most probable: thread tension too tight for a 120 gsm fabric, combined with a needle (14/90) that is heavy for the cloth, so the seam is compressed after stitching.
- Action: reduce needle tension and balance bobbin tension, set stitch length to about 2.5 mm, fit a 11/75 or 12/80 sharp needle, and check for correct presser-foot pressure. On a curve, do not pull the plies - let the feed do the work.
2. Skipped stitches at the collar point
- Most probable: needle deflection and loss of needle-to-hook clearance as the needle climbs the tapered point, worsened by lifting the presser foot to pivot.
- Action: fit a fresh sharp-point needle, check hook timing and needle-bar height, reduce foot lift, sew the point with the fabric supported, and use a point-turning technique rather than pivoting with the foot raised.
3. Brown marks and needle holes on the placket topstitch
- Most probable: needle heat - friction at high speed on a polyester blend reaches the fibre's softening range, glazing and piercing the fabric; a blunt needle and a tight needle-plate hole make it worse.
- Action: new needle, correct plate hole size, reduce speed locally or use a needle cooler/air jet, and avoid pressing directly over the marks (which sets them).
4. Seam grin at the side seam
- Most probable: stitch density too low and seam allowance too narrow for a plain-weave shirting; the yarns slip past each other.
- Action: raise to 14–15 stitches per inch, confirm 1.5 cm seam allowance, and test a French seam or overlocked edge option.
2. Evaluate the supervisor's plan to run all machines at 60% speed, using the output figures, and propose a better plan.
Read the worked answer
Assessment of the proposal
- 1,200 pieces over 12 working days needs 100 pieces per day. At 60% speed the line gives 180 per day, so the date is still met - but 40% capacity is sacrificed permanently to cure a fault that affects only the placket.
- Slowing every machine to fix needle heat also masks the real causes of puckering, skipped stitches and seam grin, so those faults will continue at 60% speed.
- Cost: at 180/day the run takes 6.7 days instead of 4 days; that idle capacity is the real loss.
Better plan
- Hold the line for a short controlled trial: 20 pieces with corrected needle size, balanced tension, 14–15 SPI and reduced placket speed only.
- Inspect 100% of the trial against the defect list and run a seam-slippage test; release the line at full speed only if the trial is clean.
- Slow only the placket operation (or fit a needle cooler), keeping the rest of the line at full speed.
- Brief all operators on the four faults with a marked-up defect sample at each machine, and add a checkpoint after 200 pieces.
Maths to justify it: at 300/day the order is complete in 4 days, leaving 8 days as buffer for rework of the first 200 pieces - far safer than a permanently slowed line.
3. What testing and documentation would you insist on before the shipment leaves, and why does each matter to the buyer?
Read the worked answer
Testing
- Seam slippage (e.g. ISO 13936-2 or ASTM D434) at the side and armhole seams: this is the only objective evidence that the seam-grin fix has worked, and it is a specified deliverable.
- Seam strength and elongation and a needle-cut/hole check on the placket: needle damage is a latent defect that appears after washing.
- Dimensional stability to a wash test (ISO 6330 / ISO 5077) so the buyer knows the 35% polyester blend will not shrink in their store's laundering instructions.
- Colourfastness to washing and rubbing if any contrast placket or collar is used.
Documentation and inspection
- In-line inspection at 200 pieces plus end-line inspection at AQL 2.5 major / 4.0 minor, with a defect Pareto showing that puckering and skipped stitches are closed out.
- An approved golden sample signed by both parties, plus the corrected machine-setting sheet (needle 11/75, 14 SPI, tension settings).
- Care label artwork matching the tested performance, and a rework record for the first 200 pieces.
Reasoning: the buyer's 2.5 AQL is a sampling limit, not a guarantee; the seam-slippage report and the golden sample are what convert a verbal assurance into a defensible record if a claim is raised later.