ITI/NCVT Sewing Technology (AITT Theory) cheat sheet

Needle-guard and eye-guard must be fitted on every industrial lockstitch machine; never remove a guard to 'improve visibility'.

Power isolation rule (LOTO): switch off, lock the isolator, and verify zero energy before threading the needle bar, changing the knife, or clearing a fabric jam.

Machine flywheel runs at 3,000-5,500 stitches/min; needle penetration injuries are the most common sewing-trade accident - keep fingers at least 3 cm from the needle path and use a stiletto/awl to guide fabric.

Colour code for portable fire extinguishers: CO2 = black (electrical), foam = cream, dry powder = blue, water = red; electrical machine fires require CO2 or dry powder, never water.

Ergonomic limits: seat height adjusted so thighs are horizontal, elbows at 90 degrees, work surface 5-10 cm below elbow height; a 5-10 minute break per hour reduces cumulative trauma to neck and shoulders.

Noise exposure limit is 90 dB(A) for an 8-hour shift; hearing protection is mandatory above that level, and two people should be able to talk at 1 m distance without shouting.

Dust and fibre control: cotton dust (lint) is a respiratory hazard - local exhaust ventilation at the cutting and overlock stations, plus a face mask when brushing or blowing lint.

First aid for a needle through the finger: do not pull out; immobilise, support the hand, and refer to hospital with the machine part if the needle is embedded.

Needle size designation: metric (Nm) = needle diameter in 1/100 mm, so Nm 90 = 0.90 mm blade; Singer sizes 9, 11, 14, 16 correspond approximately to Nm 65, 75, 90, 100.

Needle point selection: sharp (set) point for woven fabrics, ball point for knits to push between yarns instead of cutting them, cutting point for leather and coated fabrics.

Needle system codes: DBx1 and 1738 for single-needle lockstitch, DCx1 for double-needle, DPx5 for overlock/chainstitch; system must match machine type.

Stitch length (SPI) = stitches per inch; stitch density on a lockstitch is normally 10-12 SPI for light fabric, 8-10 SPI for medium, 6-8 SPI for heavy denim.

Thread tension balance: bobbin thread should sit inside the fabric, not on either surface; upper tension is adjusted by the tension dial, bobbin tension by the small screw on the bobbin case (quarter-turn increments).

Loop formation underneath the fabric usually means the upper thread is not threaded through the take-up lever, or the bobbin is wound unevenly.

Maintenance schedule: daily - remove lint from feed dog, bobbin case and needle plate, oil per manual; weekly - clean motor vents and check belt tension; monthly - check timing and replace worn feed dog.

Skipped stitches on knits are usually caused by a blunt or wrong-point needle, incorrect needle-to-fabric size, or needle deflection from a bent needle.

Fibre classification: natural (cotton, flax, wool, silk) vs man-made (regenerated - viscose, modal, acetate; synthetic - polyester, nylon, acrylic, elastane).

Cotton: absorbent, comfortable, poor elastic recovery, shrinks 3-5% unless pre-shrunk or sanforised; burns with a paper smell and grey ash.

Polyester: strong, low absorbency, thermoplastic - it melts and glows with a black bead; heat-sensitive, so iron at low temperature and avoid high needle speeds that generate friction heat.

Wool: scales give felting and shrinkage; burns with a hair smell and crushable black ash; requires ball-point needle and low-tension sewing.

Yarn count systems: Tex = grams per 1,000 m; denier = grams per 9,000 m; cotton count (Ne) = number of 840-yard hanks per pound - higher Ne means finer yarn, whereas higher Tex/denier means coarser.

Fabric weight (GSM) = grams per square metre; light shirting 80-150 GSM, medium 150-250 GSM, heavy denim/coat 250-400+ GSM.

Weave structures: plain (1/1, strongest interlacing), twill (diagonal, 2/1 or 3/1), satin (long floats, lustrous, low abrasion resistance); knit structures: single jersey, rib, interlock.

Fabric grain: warp = lengthwise (higher strength, less stretch), weft = crosswise (more stretch), bias = 45 degrees to warp (maximum stretch, used for drapes and piping).

Pre-shrinking and relaxing: spread fabric in a relaxed state for 24 hours before cutting so that residual shrinkage and spirality do not distort the cut panels.

Shrinkage allowance formula: required cut length = finished length / (1 - shrinkage %). For a 2% warp shrinkage on a 100 cm finished length, cut length = 100 / 0.98 = 102.04 cm.

Grain line must be parallel to the warp; a 1 cm deviation over a 60 cm panel causes visible twisting and garment spirality after washing.

Pattern symbols: notch = matching point, dart = V-shaped fold, grain line = arrow parallel to warp, fold line = place on folded fabric, buttonhole mark = short line, seam allowance = dashed line.

Marker efficiency (%) = (area of pattern pieces / total marker area) x 100; typical woven marker efficiency is 80-90%.

Cutting tools: straight knife for bulk lay (up to 20-30 cm high), round knife for small lays and curves, band knife for precision and fusible interlining, die cutter for high volume.

Lay height limits: fabric type and knife power determine the maximum; too high a lay causes layer shifting and inaccurate cutting.

Seam allowance standards: 1-1.5 cm for most woven seams, 0.6-1 cm for enclosed seams, 0.5 cm for overlocked edges; add ease to pattern before adding seam allowance.

Lockstitch (Class 300) uses two threads and interlocks in the middle of the fabric - strong, non-stretch, requires a bobbin.

Chainstitch (Class 400) uses two threads and forms loops on the underside - more extensible than lockstitch, used for waistbands and hems where stretch is needed; unravels if the thread end is not secured.

Overlock (Class 500) uses 3, 4 or 5 threads; 3-thread overlock for edge neatening, 4-thread for seaming knits, 5-thread for strong seams with a safety stitch.

Coverstitch (Class 600) uses 2-4 threads and produces parallel rows on the face - used for knit hems, lingerie, and decorative topstitching.

Backstitch/tacking at the start and end of a seam is required for 0.5-1 cm to prevent seam slippage; on stretch fabrics use a bartack or reverse stitch at low tension.

Stitch density for knits: 10-12 SPI with a narrow zigzag or overlock; a straight lockstitch on knits breaks when stretched beyond 10-20%.

Differential feed on an overlock: set to 1.0 for normal, 1.2-1.5 to stretch the fabric (prevents wavy seams on knits), 0.7-0.9 to gather (prevents puckering on lightweight woven).

Topstitching distance from edge is a quality spec: 2 mm, 6 mm, or 10 mm are common, and the stitch must be parallel to the edge within 1 mm.

Seam classes (ISO 4916): Class 1 superimposed (plain, French), Class 2 lapped (lap felled, flat felled), Class 3 bound (binding), Class 4 flat (flat seam), Class 5 decorative, Class 6 edge neatening, Class 7 attaching separate pieces, Class 8 single-layer edge finish.

Plain seam: right sides together, stitch 1-1.5 cm from edge, press open or to one side; used in most woven garments.

French seam: stitch wrong sides together 6 mm, trim to 3 mm, turn right sides out, stitch 6 mm; encloses raw edges, suitable for light and sheer fabrics.

Flat-felled seam: strong, double-stitched, raw edges enclosed; used for jeans, shirts, and reversible garments; width typically 6-10 mm.

Stitch types (ISO 4915): 301 lockstitch, 304 zigzag, 401 two-thread chainstitch, 504 three-thread overlock, 512 four-thread overlock, 605 coverstitch.

Seam strength test: pull the seam perpendicular to the stitch line until it ruptures; failure should occur in the fabric, not the seam, for a well-balanced seam.

Seam allowance pressing: press the seam open before topstitching; a 1-2 mm shift shows as a visible ridge on the face.

Edge neatening alternatives: overlock, zigzag, binding, pinking (for non-fraying fabrics), and French seam (self-enclosed).

Interlining: fusible (resin-coated, applied by heat press at 130-160 degrees C for 10-15 seconds) or sew-in (non-fusible, used where heat would damage the shell).

Fusing parameters: temperature, pressure, and time must all be set per the interlining supplier's specification; under-fusing causes bubbling, over-fusing causes strike-through and shine.

Zippers: closed-end (trouser fly, bags), open-end (jackets), invisible (dresses, skirts), two-way (long coats); size is measured in the closed length in cm.

Buttons: 2-hole, 4-hole, shank; button diameter in lignes (1 ligne = 0.635 mm); a 20 ligne button is about 12.7 mm.

Elastic: braided (stable), knitted (soft, stretchy), woven (firm); apply with 20-30% stretch for waistbands, and secure with a bartack or stitch through the casing.

Lace and trims: attach with a narrow zigzag or coverstitch so the trim retains stretch; avoid straight lockstitch on stretch lace.

Thread selection: polyester-core cotton-wrapped thread for general use; 100% polyester for high-strength and stretch seams; silk or fine cotton for delicate fabrics; thread should be 1 size finer than the needle.

Labels and care labels: fibre content, country of origin, care instructions, and size must be permanently attached and legible per consumer labelling rules.

Placket types: continuous (one-piece strip), two-piece, faced, and fly (trouser). A placket width is typically 2.5-4 cm finished, with the buttonhole centred on the overlap.

Pocket types: patch (applied to the surface), in-seam (set into a seam), welt (a strip of fabric covering the opening), bound (strips on both sides), flap, and slash.

Patch pocket placement: top edge parallel to the garment edge and 2-3 cm below the chest line; reinforce the top corners with a bartack or triangle stitch.

Welt pocket: the welt strip is 2-3 cm wide, the opening is 12-16 cm long; the welt must be parallel to the waistband and the ends reinforced.

Collar types: shirt (two-piece with stand and fall), one-piece (band), flat (Peter Pan, sailor), shawl (rolled), and notch/lapel (tailored jackets).

Collar attachment: interface the stand, stitch the collar to the stand, clip the curve, turn, and topstitch 2-6 mm from the edge; the collar points must be symmetrical within 2 mm.

Sleeve types: set-in (most common, requires easing), raglan (diagonal seam from neck to underarm), kimono (cut in one with the body), and dolman.

Sleeve cap ease: the sleeve cap is 1.5-3 cm larger than the armhole; distribute the ease evenly between notches and shrink with steam before stitching.

Production line types: progressive bundle system (PBS), unit production system (UPS), and modular/single-piece flow; modular flow reduces WIP and lead time.

Standard minute value (SMV) = basic time x performance rating + allowance; basic time = observed time x rating / 100.

Efficiency (%) = (standard minutes produced / minutes attended) x 100; standard minutes produced = pieces x SMV.

Line balancing: assign operations so that each workstation's cycle time is as close as possible to the takt time; takt time = available time / customer demand.

Bottleneck operation determines line output; relieve it by splitting the operation, adding a machine, or reallocating work elements.

Method study steps: select, record, examine, develop, install, maintain; use flow process charts and string diagrams to record movement.

Work measurement techniques: stopwatch time study, predetermined motion time systems (PMTS, e.g., MTM, GSD), and work sampling.

Allowances typically added: personal 5%, fatigue 4-8%, machine delay 2-5%, and contingency 2-3%.

AQL (Acceptable Quality Limit) sampling per ISO 2859-1: choose lot size, inspection level (usually II), and AQL (2.5 for major, 4.0 for minor defects); read the sample size and acceptance/rejection numbers from the table.

Defect classification: critical (safety or legal, e.g., needle fragment), major (affects saleability, e.g., broken stitch, wrong size), minor (cosmetic, e.g., slight shade variation).

Four-point system for fabric inspection: assign 1, 2, 3, or 4 points per defect based on length (up to 3 inches = 1, 3-6 = 2, 6-9 = 3, over 9 = 4); accept if points per 100 square yards are within the agreed limit.

Common stitch defects: skipped stitches (needle/thread/timing), puckering (tension, feed differential, fabric stretch), seam slippage (low stitch density, slippery fabric), and needle cuts (wrong point for knit).

Common cutting defects: off-grain (marker misalignment), mismatched plies (layer shifting), short cut (knife deviation), and notch misplacement.

Inspection stages: fabric inspection, cut panel inspection, in-line (during sewing), end-of-line (final), and pre-shipment inspection.

Root cause analysis: use the 5-Why method or fishbone (Ishikawa) diagram covering man, machine, material, method, measurement, and environment.

Zero defect tools: poka-yoke (mistake-proofing jigs), statistical process control (control charts), and first-piece approval before bulk production.

Care label symbols: washtub = washing (number = max temperature), triangle = bleaching, square with circle = tumble drying, iron = ironing (dots = temperature: 1 dot 110 C, 2 dots 150 C, 3 dots 200 C), circle = dry cleaning.

Ironing temperatures: cotton 180-220 C, linen 200-230 C, wool 150-160 C with a damp cloth, silk 120-140 C, polyester 110-150 C, nylon 100-120 C.

Pressing equipment: flat bed press for general pressing, steam press with vacuum table for shaping, trouser topper, and sleeve board for narrow areas.

Pressing sequence: press seams open, press darts, shape with steam, then final press; never press over a button or zipper - use a pressing cloth.

Shrinkage testing: wash a 50 x 50 cm sample per the care instructions, dry, re-measure; length shrinkage % = (original - final) / original x 100.

Colour fastness tests: wash fastness, rub (crocking) fastness, light fastness, and perspiration fastness; ratings 1-5, with 4-5 acceptable for most apparel.

Packaging: polybag with a suffocation warning for children's wear, size and colour sticker, barcode, and carton packing list; carton dimensions must not exceed the buyer's specification.

Final finishing: thread trimming, spot cleaning, checking for needle fragments (metal detector), and folding to the buyer's fold card.

Cost sheet components: direct material (fabric, trims, thread), direct labour, factory overhead, and administrative/selling overhead; add profit margin to get the selling price.

Fabric consumption per garment = marker area per size / garment area, expressed in metres per piece; multiply by fabric rate to get fabric cost.

CMT (cut, make, trim) costing: CMT price = labour + overhead + profit, excluding fabric; FOB price includes fabric, trims, CMT, packing, and export costs.

Break-even point (units) = fixed cost / (selling price per unit - variable cost per unit).

Markup vs margin: markup % = (price - cost) / cost x 100; margin % = (price - cost) / price x 100; a 25% markup equals a 20% margin.

Lead time = sampling + fabric procurement + production + inspection + shipping; a typical export order needs 90-120 days.

Workplace communication: use standard terminology (style number, colour code, size ratio), written approval for changes, and a documented handover at shift change.

Small-business registration and compliance: GST registration above the turnover threshold, labour welfare compliance, and a written employment contract with wage and working-hour terms.

AQL (Acceptable Quality Limit) sampling per ISO 2859-1: choose lot size, inspection level (usually II), and AQL (2.5 for major, 4.0 for minor defects); read the sample size and acceptance/rejection numbers from the table.

Defect classification: critical (safety or legal, e.g., needle fragment), major (affects saleability, e.g., broken stitch, wrong size), minor (cosmetic, e.g., slight shade variation).

Four-point system for fabric inspection: assign 1, 2, 3, or 4 points per defect based on length (up to 3 inches = 1, 3-6 = 2, 6-9 = 3, over 9 = 4); accept if points per 100 square yards are within the agreed limit.

Common stitch defects: skipped stitches (needle/thread/timing), puckering (tension, feed differential, fabric stretch), seam slippage (low stitch density, slippery fabric), and needle cuts (wrong point for knit).

Common cutting defects: off-grain (marker misalignment), mismatched plies (layer shifting), short cut (knife deviation), and notch misplacement.

Inspection stages: fabric inspection, cut panel inspection, in-line (during sewing), end-of-line (final), and pre-shipment inspection.

Root cause analysis: use the 5-Why method or fishbone (Ishikawa) diagram covering man, machine, material, method, measurement, and environment.

Zero defect tools: poka-yoke (mistake-proofing jigs), statistical process control (control charts), and first-piece approval before bulk production.

Care label symbols: washtub = washing (number = max temperature), triangle = bleaching, square with circle = tumble drying, iron = ironing (dots = temperature: 1 dot 110 C, 2 dots 150 C, 3 dots 200 C), circle = dry cleaning.

Ironing temperatures: cotton 180-220 C, linen 200-230 C, wool 150-160 C with a damp cloth, silk 120-140 C, polyester 110-150 C, nylon 100-120 C.

Pressing equipment: flat bed press for general pressing, steam press with vacuum table for shaping, trouser topper, and sleeve board for narrow areas.

Pressing sequence: press seams open, press darts, shape with steam, then final press; never press over a button or zipper - use a pressing cloth.

Shrinkage testing: wash a 50 x 50 cm sample per the care instructions, dry, re-measure; length shrinkage % = (original - final) / original x 100.

Colour fastness tests: wash fastness, rub (crocking) fastness, light fastness, and perspiration fastness; ratings 1-5, with 4-5 acceptable for most apparel.

Packaging: polybag with a suffocation warning for children's wear, size and colour sticker, barcode, and carton packing list; carton dimensions must not exceed the buyer's specification.

Final finishing: thread trimming, spot cleaning, checking for needle fragments (metal detector), and folding to the buyer's fold card.

Cost sheet components: direct material (fabric, trims, thread), direct labour, factory overhead, and administrative/selling overhead; add profit margin to get the selling price.

Fabric consumption per garment = marker area per size / garment area, expressed in metres per piece; multiply by fabric rate to get fabric cost.

CMT (cut, make, trim) costing: CMT price = labour + overhead + profit, excluding fabric; FOB price includes fabric, trims, CMT, packing, and export costs.

Break-even point (units) = fixed cost / (selling price per unit - variable cost per unit).

Markup vs margin: markup % = (price - cost) / cost x 100; margin % = (price - cost) / price x 100; a 25% markup equals a 20% margin.

Lead time = sampling + fabric procurement + production + inspection + shipping; a typical export order needs 90-120 days.

Workplace communication: use standard terminology (style number, colour code, size ratio), written approval for changes, and a documented handover at shift change.

Small-business registration and compliance: GST registration above the turnover threshold, labour welfare compliance, and a written employment contract with wage and working-hour terms.