Machine No. 3: Skipped Stitches Before a School Shirt Deadline
A tailoring workshop in a school-cum-training centre runs six straight-stitch machines for 6 hours a day. A student operating machine No. 3 reports that the thread loops underneath the cotton fabric, stitches skip every 8–10 stitches, and the needle has broken twice in one week. The machine was last serviced eight months ago. The needle currently fitted is size 14, the thread is 40s cotton, the tension dial is at 4, and the bobbin was wound on another machine. The workshop has no overlock machine, the delivery of 40 school shirts is due in five days, and the instructor must decide whether to keep the machine running, switch the student to another machine, or stop for repair. The workshop has a spare packet of size 11 and size 16 needles, a small brush, machine oil, and a screwdriver. The fabric being stitched is a light cotton shirting.
1. List the likely causes of the skipped stitches and looping in the most probable order, and state the first three checks you would make before changing the tension dial. Explain why the order matters.
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The symptoms point to a machine problem rather than a single tension fault. Most probable order:
- Needle condition/size: size 14 with 40s cotton on light shirting can work, but two breakages in a week suggest a bent, blunt or wrongly set needle. A bent needle can cause skipped stitches and loops.
- Bobbin/bobbin case: a bobbin wound on another machine may be uneven or the wrong height; this commonly causes loops underneath.
- Lint/thread nest: under the throat plate, in the feed dog or around the bobbin case. Eight months without service makes this likely.
- Timing/clearance: check only after the simple causes are eliminated.
- Upper tension: adjust last. Changing tension first can hide the real cause and make the next test meaningless. First checks: remove the needle and roll it on a flat surface; replace with a new size 14 (not 11 or 16) and rethread; remove the bobbin case and brush out lint; test on two layers of scrap. If loops persist after a new needle, a correctly wound bobbin and cleaning, stop and call a technician.
2. The instructor has a spare size 11 and size 16 needle, a brush, machine oil and a screwdriver. Give a 15-minute care routine and a longer maintenance schedule; say which tasks a student may do and which need a technician.
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15-minute routine: brush lint from the bobbin case, feed dog and under the throat plate; check the needle for straightness and sharpness; oil one or two drops only at the points marked in the manual; wipe excess oil; run a test seam on scrap. The student may do brushing, needle changing, external oiling and test-sewing under supervision. Weekly: remove the face plate, clean compacted lint, check the belt tension, cord, plug and pedal; check that the bobbin winder winds evenly. Longer schedule: because the machine was last serviced eight months ago, request a technician check of timing, tension spring, motor, internal gears and wiring. A student must not open the internal mechanism or adjust timing. Keep a log with date, machine number, action and result. A machine that has just been repaired should be test-sewn on actual fabric before it returns to production.
3. Should the workshop keep machine No. 3 running to meet the five-day deadline? Recommend an action and write a short machine log entry.
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Do not keep running it as it is. Skipped stitches create weak seams and rework, and a broken needle can fly and injure the student. The deadline is still manageable: 40 shirts across the five other machines is 8 shirts per machine over five days, which is realistic if the work is reallocated. Recommended action: stop machine No. 3 for diagnosis and repair; move the student to another machine after a test seam; use machine No. 3 only for non-load-bearing basting after repair, not for visible seams. Machine log entry: Date/time: [today]; Machine: No. 3; Symptoms: loops underneath, skipped stitches every 8–10 stitches, two needle breaks in one week; Actions: fitted new size 14 needle, cleaned bobbin case and feed dog, changed bobbin, tested on scrap; Result: fault persists/clears; Decision: call technician; Operator: student name. This record helps the instructor identify a repeat fault and avoid blaming the operator.