Lesson 1Tension systems: upper and bobbin tension checking and fixing stepsGet confident fixing thread tensions for steady stitches. Learn how upper and bobbin tensions work together, spot imbalance from seam looks, and do careful fixes and tests without going too far.
Reading stitch balance on top and undersideTesting and setting bobbin case tension rangeAdjusting upper tension and check spring actionEffects of thread size and fabric on tensionRecording baseline settings for repeatabilityLesson 2Bearing, shaft, and oiling problems causing heat: spotting and fixingLearn how bearing and shaft issues make heat, how bad oiling speeds up wear, and how to spot overheating early by touch, smell, and tools, then do safe fixes to get smooth, cool running.
Typical overheating symptoms and risk indicatorsChecking bearings and shafts for play and scoringAssessing oil level, grade, and delivery pathsUsing temperature, smell, and noise for diagnosisCorrective steps and post-repair verificationLesson 3Needle types, sizes, and materials for medium denim; picking right needle and spotting wearFocus on needles for medium denim. Compare needle types, sizes, materials, match to thread and cloth, and spot wear, damage, small faults that spoil stitch quality and cause breaks.
Needle systems used on industrial lockstitch unitsChoosing size and point for denim and threadCoatings and materials for heat and wear controlVisual and tactile signs of needle wear or damageReplacement intervals and documentation habitsLesson 4Thread path and common threading mistakes causing breaksFollow the full thread path and learn where mistakes happen. Spot wrong routing, missed guides, tension skips causing breaks, skipped stitches, fraying, then use a repeat threading check routine.
Mapping the full upper thread pathCommon misrouting points and missed guidesBobbin winding and insertion best practicesThread quality issues that mimic path faultsStandardized threading and double-check stepsLesson 5Stitch formation, stitch length parts, and reasons for uneven stitch lengthUnderstand how lockstitch forms and what sets stitch length. Study feed parts, stitch controls, common uneven length causes so you fix even, right stitches on denim and like materials.
Sequence of lockstitch formation step by stepFeed dog motion and stitch length regulatorEffects of presser foot pressure on feedingSlippage, drag, and operator handling issuesInspection and adjustment of feed componentsLesson 6Parts of industrial lockstitch machines: needle bar, shuttle/hook, bobbin case, feed dogs, presser foot, tension partsStudy main parts of industrial lockstitch machine and how they work to make stitch. Spot needle bar, hook, bobbin case, feed dogs, presser foot, tension units to trace faults to right parts.
Needle bar, clamp, and driving mechanismsShuttle or rotary hook and bobbin case layoutFeed dog, throat plate, and presser foot rolesUpper tension, check spring, and guidesDrive train, handwheel, and belt connectionsLesson 7Hook and timing problems: signs, measuring, simple timing checksSpot signs of hook and timing faults like skipped stitches, thread breaks. Learn basic timing measures, check needle-hook links, when simple fixes safe for field techs.
Visual symptoms of timing and hook problemsMeasuring needle height at hook intersectionChecking hook point clearance and positionSimple timing corrections within safe limitsWhen to escalate to advanced timing serviceLesson 8Tools and supplies list for site checks and fixes (feel gauges, screwdrivers, oil, spare needles)Get ready for site work with practical toolkit. Make list of hand tools, gauges, oils, cleaners, supplies like needles, screws so most checks and fixes done in one go.
Essential screwdrivers, wrenches, and pliersFeeler gauges, rulers, and timing scalesOils, greases, and cleaning materialsAssorted needles, screws, and small hardwareOrganizing and transporting a mobile tool kitLesson 9After-fix testing: test-seam steps, speed build-up, stitch quality pass rulesCheck fix quality with controlled sewing tests. Set test cloths, run slow to fast seams, check stitch balance, seam look, use clear pass rules before back to work.
Preparing test fabric, thread, and needle setupLow-speed functional checks and observationsProgressive speed testing and heat monitoringEvaluating stitch balance and seam appearanceDefining pass, rework, and documentation rulesLesson 10Step-by-step sight check list and hand tests (handwheel turn, needle drop, bobbin check)Use structured sight check and hand test before power on. Check outside state, guards, wires, moving parts, turn handwheel, test needle drop, check bobbin hook safe.
Exterior, guards, and wiring visual checklistChecking belts, pulleys, and moving clearancesHandwheel rotation feel and noise assessmentNeedle drop alignment and clearance checksBobbin, case, and hook area inspection stepsLesson 11Common fixes: re-threading, needle change, tension tweaks, hook clean, oiling, part swapPractice top field fixes. Learn steady re-threading, safe needle swaps, tension tune, hook clean polish, oil routines, when worn parts need swap not tweak.
Standardized re-threading and path verificationSafe needle removal, fitting, and alignmentFine-tuning upper and bobbin thread tensionsHook cleaning, deburring, and lubrication stepsCriteria for replacing worn or damaged partsLesson 12Thread types and qualities for denim: strength, twist, oils, right thread sizeLook at threads for denim like polyester, cotton, corespun. Compare strength, twist, finishes, sizes, how thread pick affects needle heat, tension, seam strength, look.
Common thread fibers for denim applicationsThread size selection for seams and topstitchingTwist direction, ply count, and seam behaviorLubricants and finishes that reduce frictionMatching thread, needle, and tension settingsLesson 13Heat and needle bend causes: friction, wrong needle, timing faults, high speed effectsKnow why needles heat bend under work from friction, bad needle, timing wrong, too fast. Trace signs to real causes, do aimed tweaks to stop repeats.
Friction sources at needle, fabric, and threadEffects of incorrect needle size and point typeTiming errors that overload or deflect the needleHigh-speed operation and inadequate coolingPreventive adjustments and operator guidanceLesson 14Safety steps and pre-checks for lockstitch machines (lockout/tagout, power cut, handwheel tests)Build safe ways before touch lockstitch machine. Do lockout tagout, check power cut, controlled handwheel tests so checks tweaks no shock, tangle, hurt risk.
Lockout and tagout steps for sewing stationsVerifying power off and residual energy releaseGuarding, PPE, and safe body positioningSafe handwheel rotation and needle clearance testsDocumenting hazards and communicating with operators
