Machine Setup, Threading, Tension Adjustment and Basic Maintenance
This domain tests the sequence you follow to bring a machine into production, the correct threading path, how upper and lower tension interact, and the daily and periodic maintenance routine.
Setup sequence
Clean lint, oil per the manual, fit a new needle the right way round (flat side per machine), insert the correct bobbin, thread from spool to needle, set stitch length and tension, then sew a test seam on the actual fabric and check both sides.
Threading rules
- Raise the presser foot while threading so the tension discs open and the thread seats between them.
- Follow the path in order: spool pin, guide, tension discs, check spring, take-up lever, lower guides, needle. Skipping the take-up lever gives loose, tangled stitches.
- Wind the bobbin evenly at correct tension; an uneven bobbin changes stitch balance as it unwinds.
Tension balance
Upper tension is set by the dial; bobbin case tension by its screw, adjusted only in small increments. A balanced 301 stitch locks inside the fabric, with no loops on either face. Loops under the fabric mean the upper tension is too loose (or the bobbin too tight); loops on top mean the bobbin is too loose (or the upper too tight). Always re-test on scrap after each change.
Maintenance
- Each shift: remove lint from feed dog, hook and tension discs; oil the points listed in the manual.
- Needle change at least every shift or after about 8 hours, and immediately after a needle break.
- Periodic: hook timing and needle-to-hook clearance (about 0.05 mm), belt tension, worn feed dog, throat plate burrs, electrical checks by a qualified person.
- Over-oiling stains fabric; use only the specified oil.
Worked example
A machine starts a seam with a nest of tangled thread under the fabric. Reasoning: hold both thread tails back for the first few stitches, check that the bobbin is wound evenly and seated correctly, confirm the thread is in the tension discs with the foot up during threading, then rebalance tension on scrap.
Traps that cost marks
Reaching for the bobbin screw first, threading with the presser foot down, and changing tension without a test seam.