Sewing Techniques and Garment Construction
Sewing Techniques and Garment Construction
This domain tests stitch classes, seam types, machine settings and construction sequence. You should know why a lockstitch differs from an overlock and how stitch density affects seams.
Core concepts
- Stitch classes: 100 = single-thread chain; 300 = lockstitch (commonly 301); 400 = multi-thread chain; 500 = overedge/overlock. Overlock neatens edges and allows stretch; lockstitch is strong and less stretchy.
- Seam types: plain, French, flat-felled and overlocked. French seams enclose raw edges and suit lightweight fabrics; flat-felled seams are strong and common on jeans and home textiles.
- Stitch density: measured in stitches per inch (SPI). Woven garments commonly use 10–12 SPI; knits need a stitch that stretches, such as a narrow overlock or coverstitch.
- Machine settings: match needle size and thread to fabric weight; check tension on a scrap before sewing the garment.
Worked example
A seam is 80 cm long and the machine is set at 12 SPI. Convert length: 80 ÷ 2.54 = 31.5 inches. Stitches = 31.5 × 12 = 378 stitches. If the seam is resewn after a fault, thread consumption roughly doubles for that seam, so costing must allow for rework.
Marks-losing traps
Using a lockstitch on a stretch knit without adjusting; setting a very high SPI that perforates or puckers fabric; forgetting seam allowance in construction; testing tension on the garment instead of a scrap; trimming seam allowance before checking fit.
Key points
- 300-class lockstitch is strong; 500-class overlock neatens and stretches.
- French seams enclose edges; flat-felled seams are strong.
- SPI controls stitch density; match it to fabric and product.
- Test needle, thread and tension on scrap fabric.
- Rework adds thread, time and cost.