Sixty rib T-shirts, three days, skipped stitches

Skipped stitches on the overlocker The most likely causes, in order of probability:

1. Wrong needle for a knit. A 90/14 universal has a sharp point that can deflect off or cut the rib's loops instead of entering the needle groove cleanly. On 1x1 rib the loop must be entered without cutting yarns. Fit a ballpoint (SES/jersey) needle: 75/11 for the body seams, 80/12 where the shoulder and neckline stack is thicker.
2. Needle deflection. If the operator pulls the fabric, the needle bends, the loop is missed and the stitch skips. The fabric must be guided, never pulled; the differential feed moves it.
3. Needle bar height and looper timing. If neither has been checked since the machine was last serviced, check both before anything else, since no needle change will fix timing.
4. Needle seating and plate wear. Confirm the needle is fully up in the clamp, and check the needle plate hole for a burr or an oversized opening that lets the fabric drop.
5. Tension. Very high needle tension increases deflection at speed on thick stacks; balance tensions on a scrap before running.

Broken needles A needle normally breaks when it strikes something hard, or when it is deflected into the plate or looper. With no pins in use, check timing and needle bar height first, then the needle plate, presser foot and any needle guard. Confirm the correct needle system and that needles are not already bent before fitting - a bent needle in a rib seam breaks within metres.

Set-up before production Fit 75/11 ballpoint in both needle positions, check timing, set differential feed to 1.2-1.4, reduce presser foot pressure, re-thread, and sew off on four layers of the actual fabric until ten consecutive shoulder seams are clean. Change needles every 8 hours of running and log it.

Wavy neckline binding Causes: the binding is stretched as it is sewn, or the neckline itself is stretched; the binding is the wrong length or cut on the wrong grain; the differential feed at 1.0 lets the fabric run under tension. Fixes:

1. Cut the binding on the crosswise grain of the rib, which is where it stretches, and cut it to about 85-90% of the measured neckline circumference plus seam allowance. Measure the neckline, do not estimate.
2. Steam-shrink the binding before sewing and let it cool flat. This recovers stretch that has already crept in.
3. Mark quarters on both the neckline and the binding. Sew with the binding underneath and slightly stretched, the neckline on top and not stretched.
4. Set the differential feed to 1.2-1.4 and reduce presser foot pressure so the machine feeds rather than drags. Use a walking foot if one is available for the single-needle stage.
5. Stabilise the shoulder seams with clear elastic or fusible tricot tape before the neckline goes on; a stretched shoulder pulls the neck out of shape.
6. Wash-test a sample at 40 °C and measure the neckline against spec before running the batch.

Coverstitch tunnelling and flaring Causes: excessive needle and looper tension pulling the seam into a ridge, differential feed too low, stitch too long, or the hem stretched during sewing. Fixes:

1. Reduce looper tension first, then needle tensions, until the hem lies flat on a scrap of the actual fabric.
2. Differential feed 1.3-1.5 and stitch length 2.5 mm.
3. Buy woolly nylon for the looper. It is inexpensive and it is the standard fix for recovery and softness; without it the hem will always be firmer than the fabric.
4. Support the fabric in front of and behind the needle; do not pull the hem through.
5. Sew and wash a test hem before committing the batch.

Day 1, morning - prove the set-up (the spare hour, taken before production starts)

• Both overlockers: 75/11 ballpoint needles, correct threading, differential 1.3, reduced presser foot pressure, timing and needle bar height checked. Sew off on four layers of rib until ten consecutive clean shoulder seams.
• Coverstitch: new needles, reduced tensions, differential 1.4, woolly nylon in the looper.
• Sew a test neckline, shoulder and hem on the actual fabric. Wash one sample at 40 °C, dry, and measure. Production does not start until this passes.

Day 1 afternoon to day 2 - run in bundles of ten

• After every bundle, check three things: skipped stitches present or absent, neckline measurement within ±0.5 cm, hem width and flatness. Stop the line if a bundle fails; a fault caught at bundle one costs ten garments, at packing it costs sixty.
• Day 2 afternoon: a second wash test taken from the production run, not from the test sample.

Day 3 - finish and inspect

• Press, 100% inspection on a light table for stretched necklines, tunnelling, needle cuts and oil marks, then pack and count to 60.

Rules for the workshop wall

• Settings are proven on the actual fabric, never copied from the manual.
• Needles are consumables: change every 8 hours or after a break, and log it.
• Nobody pulls fabric through a machine.
• Quality gates after each bundle, not a single final inspection.
• If the buyer's standard cannot be met by day 3, say so on day 2, not on day 3. A late honest call protects the account; a late surprise does not.