Industrial Sewing Machine Fundamentals: Types, Parts, Needles, Threads and Attachments
Expect questions that ask you to name the machine for a given job, identify a part from its function, match a needle system or size to a fabric, and choose the right thread or attachment.
Machine types and what they make
- Single-needle lockstitch (stitch class 301): the general-purpose seaming machine.
- Overlock: 3-thread for edge neatening, 4-thread for knit seaming, 5-thread safety stitch for seaming plus neatening in one pass.
- Flatlock/coverstitch: stretch hems and flat joins on knits.
- Feed-off-the-arm: flat-fell seaming on denim, especially inseams.
- Bartack and buttonhole machines: reinforcement and buttonholes.
- Specials: blind hem, zigzag, chainstitch, double-needle.
Parts and their functions
Needle and needle bar; presser foot; feed dog; throat plate; bobbin and bobbin case; rotary hook (or shuttle); take-up lever; tension discs and check spring; thread guides; spool pin; handwheel; reverse lever; stitch-length dial.
Needles
- Lockstitch uses the DBx1 (16x231) system; overlock typically DCx27; coverstitch uses UY128GAS. Systems are not interchangeable.
- Metric sizes run about 60 to 110 (Singer 8 to 18). Finer fabric, finer needle: lightweight georgette around 65-70, shirting around 80, denim around 100-110.
- Point type matters: sharp (SES) for wovens, ball point (SUK) for knits so yarns are pushed aside, cutting point for leather and coated fabrics.
Threads and attachments
Threads are sized by ticket number (higher ticket = finer) or tex. Polyester core-spun is the workhorse; cotton for natural handle; nylon for high strength. Attachments include hemmers, binders, folders, zipper and compensating feet, edge and magnetic guides, and tuckers.
Worked example
A cotton jersey T-shirt side seam is skipping and the needle is leaving small holes. Reasoning: the sharp needle is cutting knit loops, so switch to a ball-point needle of the correct size (for example 80/12 SUK), match thread to the fabric weight, then recheck tension on a scrap.
Traps that cost marks
Treating DBx1 and DCx27 as interchangeable, using a ball point on woven fabric, and choosing an oversized needle that leaves permanent holes in coated or fine fabric.