Stitching Techniques, Seams and Stitches
Scope
Stitch types (ISO 4915), seam classes (ISO 4916), tension, SPI and seam selection.
Core rules
- Stitch classes: 100 single-thread chain, 300 lockstitch, 400 multi-thread chain, 500 overedge, 600 cover chain.
- Seam classes: 1 superimposed, 2 lapped, 3 bound, 4 flat, 5 decorative, 6 edge neatening, 7 separate items, 8 single ply.
- Common seams: plain, French (class 1, enclosed), flat-fell (class 4, two rows), lapped, bound.
- Tension: balanced lock inside the fabric; overlock needle and looper threads interlock at the fabric edge.
- Knits need stretch; use 500 or 600 stitches with suitable differential feed. Test seam strength, slippage and elongation.
Worked example
Choose a seam for the inside leg of denim jeans. Reasoning: it needs strength and abrasion resistance, and raw edges must be enclosed. A flat-fell seam (class 4) with two rows of lockstitch gives a strong, clean finish; a plain seam would fray. Set stitch length about 3 mm and use a 100/16 or 110/18 needle.
Traps
Using a lockstitch on stretch knits without elastane thread; excessive SPI causing thread breakage and puckering; unbalanced overlock causing seam grin; wrong seam class for the finish.