Sewing Equipment, Stitches and Seams
Equipment and stitch classes
The exam tests machine selection, ISO stitch classes and seam choice. Common machines: lockstitch (301), overlock (500-class overedge), coverstitch (600-class), blind-hem and buttonhole machines. Needle size and thread ticket must suit fabric weight; tension should form balanced stitches without puckering.
Seam and stitch rules
- Class 100 single-thread chain; 300 lockstitch; 400 multi-thread chain; 500 overedge; 600 coverstitch.
- Seam classes: class 1 superimposed, class 2 lapped, class 3 bound, class 4 flat, class 5 ornamental, class 6 edge neatening.
- Overlock both sews and neatens; a 4-thread overlock is common on knit side seams.
- SPI (stitches per inch) affects strength and stretch; knits need lower SPI and stretch stitches.
Worked example
A cotton T-shirt needs side seams and a hem. Choose a 4-thread overlock for the side seam because it gives stretch and edge neatening in one pass; choose a coverstitch for the hem because it stretches with the knit and covers the raw edge. Reasoning: the seam must move with the fabric; a 301 lockstitch alone would crack under stretch unless sewn with a stretch technique.
Traps
Do not label overlock as class 400; overedge is 500. Do not use a straight lockstitch on a stretch knit without adjustment. A seam is not the same as a stitch: a seam joins pieces, a stitch is the thread formation. Balanced tension is not tightest possible.