Sewing Machine Parts, Setup and Basic Maintenance
This domain tests identification of lockstitch and overlock machine parts, correct needle and threading set-up, tension and stitch-length setting, and the daily maintenance routine that keeps stitch quality stable.
Main parts and function
- Needle bar, presser bar and presser foot, needle (throat) plate, feed dog, bobbin case and bobbin, rotary hook, take-up lever, thread guides, tension discs, spool pin, handwheel, reverse lever, stitch-length regulator, servo motor, oil reservoir.
- The feed dog moves fabric; the hook picks the needle loop; the take-up lever controls thread supply and setting of the stitch.
Needle and thread set-up
- Needle system: DBx1 for woven lockstitch; ball-point for knits; heavier sizes for denim.
- Sizes: 70/10 for fine voile, 80/12 for shirting, 90/14 for medium wovens, 100/16–110/18 for denim and canvas.
- Insert the needle fully up into the clamp with the scarf facing the hook, then tighten securely.
- Thread path: spool, guides, tension discs, take-up lever, needle - in that order. Missing one guide causes looping.
- Stitch length 2.5–3 mm for shirting (about 10–12 SPI); shorter, 12–14 SPI, for knits.
Tension and maintenance
- Correct tension: the knot sits inside the fabric, not on the face or back.
- Brush lint from feed dog, bobbin case and hook area at least once per shift; lint causes skipped stitches and oil starvation.
- Oil per the manual in the marked holes; over-oiling stains fabric and attracts lint.
- Replace the needle after a break, after a burr, and roughly every 8 hours of running.
Worked example
Skipped stitches appear on a single-jersey knit. Check in order: is a ball-point needle fitted and fully inserted? Is the needle blunt or burred? Is the thread path correct? Then check hook timing. Reasoning: a sharp needle cuts knit loops, so the hook has nothing to pick up.
Traps
- Tightening top tension to fix a loose stitch actually caused by lint trapped in the bobbin case.
- Keeping a burred needle because it "still sews" - it snags and needle-cuts fabric.
- Ignoring oil quantity and oil type, which shortens hook life.