Sixty School Shirts: Choosing Stitches Without an Overlock Machine
A tailoring unit has received an order for 60 school shirts in cotton–polyester fabric. The unit has four straight-stitch machines and one machine with zigzag, but no overlock machine. The agreed stitch length is 2.5 mm, needle size 14, and 40s polyester thread. A pre-production sample washed three times shows puckering along the side seams and frayed seam edges; one machine also produces irregular stitch length. The supervisor wants to finish all side seams, armholes, hems and the elastic casings of the sports shorts ordered with the shirts using only the straight stitch to save time. The delivery is in 10 days, and 8 shirts have already been stitched with the longest stitch length available. The unit has spare needles, a seam ripper, and scrap fabric for tests. The shirts must survive repeated school washing.
1. Recommend the stitch type and seam finish for side seams, armholes, hems and elastic casings. Explain why straight stitch alone is not adequate for all these areas.
Read the worked answer
Side seams: straight stitch at 2.5 mm with 1 cm seam allowance, backstitch at both ends; finish the raw edges with zigzag (about 3–4 mm width, 2–2.5 mm length) or a double-stitched turned edge. Armholes: stitch the seam, trim graded allowances, then zigzag or use a French seam if the fabric is light enough; for school shirts a plain seam with zigzag finish is practical. Hems: double-fold 1 cm + 1 cm and straight stitch at 2.5 mm; the raw edge is enclosed, so zigzag is not needed. Elastic casing: straight stitch at 2.5 mm, leave a 2 cm opening, reinforce the opening; zigzag is not necessary because the edges are folded. Straight stitch alone is not adequate on exposed seam edges because cotton–polyester frays in repeated washing. Zigzag or an enclosed seam spreads the finishing load and prevents the seam from opening. Load-bearing seams also need a shorter stitch, not the longest stitch, to avoid grinning.
2. What checks would you make on the 8 shirts already stitched at the longest stitch length, and what will you do with them?
Read the worked answer
Inspect each shirt before it goes forward:
- Measure stitch length on the seam; 2.5 mm is about 10–11 stitches per inch. The longest stitch is likely 4–5 mm and is too weak for a side seam.
- Gently pull the seam across its width. If the seam grins or the thread looks straight and loose, it is a reject.
- Check seam allowance. If unpicking leaves at least 8–10 mm, unpick and restitch at 2.5 mm. If unpicking would leave too little allowance, add a second row of stitching or a strengthening tape rather than restitching in the same line.
- Re-finish any raw edges with zigzag and wash one repaired sample again. Do not send them out merely because they are already stitched. Record how many were reworked and why, so the supervisor can see the cost of using the longest stitch to save time.
3. Explain how you would set and test a machine before bulk stitching, including needle, thread, tension and cleaning.
Read the worked answer
Fit a new size 14 needle, check that it is fully inserted and tightened. Use 40s polyester thread on top and in the bobbin; wind the bobbin evenly on the same machine. Set stitch length to 2.5 mm and start with tension at 4. Clean lint from the bobbin case, feed dog and throat plate. Test on two layers of the actual cotton–polyester fabric, plus a test with interfacing at the collar area. Check the top and bottom for loops, skipped stitches and puckering. Adjust tension one step at a time, then re-test; do not adjust several settings at once. For the machine producing irregular stitch length, have a technician check it before it is used on visible seams. Clean the machine after each 8-hour shift.