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C

Piece C

Sergers and coverstitch

A serger trims the edge, sews the seam and overcasts it in one pass. A coverstitch machine sews the stretchy, twin-row hems you see on T-shirts. Neither replaces a sewing machine for zippers or buttonholes.

Common serger setups
2, 3 or 4 threads, some 5
Coverstitch
2 or 3 needles with one looper

A 4-thread overlock is the usual seam for knits: two needles and two loopers, with a knife trimming the edge just ahead of the needles. A 3-thread overlock is lighter and is used for finishing edges and rolled hems.

Differential feed runs the front and rear feed dogs at different speeds. Turn it up to stop knits from stretching out and waving; turn it down to stop light wovens from puckering. Look for easy looper threading, since threading is what most new owners find hardest.

A coverstitch sews two or three parallel rows of needle thread on top with a looper thread underneath, which stretches with the fabric. Some combination machines do both serging and coverstitch, but switching between them takes a few minutes of conversion.

Four-thread overlock seam with left and right needle lines, upper and lower looper threads and the knife cut edgefabric feeds this wayLeft needleRight needleUpper looperLower looperKnife cut edgewidest seamnarrow seamon top, wraps the edgeunderneath (dashed)trims just ahead of needlesDifferential feed sets the front feed dogs faster or slower than the rear ones as the fabric moves through.
Leave out one needle for a 3-thread overlock: the left needle gives a wider seam, the right needle a narrower one.

Common mistakes

  • Expecting a serger to sew zippers, buttonholes or topstitching.
  • Using household needles when the manual names a different needle system.
  • Leaving differential feed at neutral on knits that keep stretching out.

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