ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) cheat sheet

Fire classes and media: A (solid combustibles) water/foam; B (flammable liquids) foam, CO2, dry powder; C (flammable gas) isolate supply then dry powder; D (combustible metals such as Al, Mg swarf) dry sand or graphite powder, never water; E (live electrical) CO2 or dry powder only after isolation.

Noise exposure: 90 dB(A) for an 8-hour day is the usual statutory limit; at 85 dB(A) hearing protection and audiometry are triggered, and the 3 dB exchange rate halves permissible exposure time for every 3 dB rise.

Abrasive wheels: confirm the marked maximum peripheral speed and rpm match the machine spindle, ring-test before mounting, fit a guard covering at least three-quarters of the wheel, and keep the work rest gap within 3 mm.

Lockout/tagout sequence: isolate the supply, dissipate stored energy (accumulator pressure, springs, suspended loads, gravity), apply lock and tag, then verify zero energy with a voltmeter and pressure gauge before dismantling.

PPE selection rules: chip-making and grinding - impact goggles plus face shield; arc welding - shield with shade 10–13 and leather gauntlets; hydraulic work - oil-resistant gloves and eye protection; no loose sleeves, rings or wristwatches near rotating spindles.

Portable electrical tools: supply through a 30 mA RCCB, verify earth continuity, insulation resistance not below 1 MΩ, and use 110 V centre-tapped-earth supply in damp or confined locations.

Manual handling rule: keep the load close to the body and lift with the legs, never with a twisted trunk; loads above roughly 25–40 kg require a team lift or a mechanical aid per ILO and IS guidance.

Chemical control: obtain the safety data sheet before use, extract coolant mist and solvent vapour at source with local exhaust ventilation, and maintain machine coolant at pH 8.5–9.5 with regular microbial checks to prevent dermatitis.

Housekeeping and 5S: keep walkways clear of at least 1 m, cover chip bins, absorb oil spills immediately, and never clean skin or clothing with compressed air - it can inject air and debris under the skin.

Vernier least count = 1 main scale division − 1 vernier scale division; for a 1 mm main scale and a 50-division vernier spanning 49 mm, LC = 0.02 mm. Reading = main scale + (coinciding vernier division × LC), with zero error applied with opposite sign.

Micrometer least count = screw pitch ÷ thimble divisions = 0.5 mm ÷ 50 = 0.01 mm; verify zero with the anvils closed and use the ratchet to limit measuring force to about 5–10 N.

Slip gauges: wring by sliding, never rubbing; sets M87 and M112 build a dimension with the fewest blocks; grades 00, 0, I and II from highest to lowest accuracy; calibration is referenced to 20 °C.

Sine bar: sin θ = h/L, where h is the slip gauge stack height and L the roll centre distance (100, 200, 250 or 300 mm); accuracy falls off above 45°, so prefer angle gauges or a rotary table beyond that.

Hole-basis fits: H7/g6 sliding clearance, H7/f7 running clearance, H7/k6 transition, H7/p6 interference; IT01 is the finest tolerance grade and IT16 the coarsest.

Surface roughness: Ra is the arithmetic mean deviation (CLA), Rz the maximum profile height, Rt the total height; always state the cutoff (commonly 0.8 mm) and the units (µm). Ra 1.6 µm corresponds approximately to roughness grade N7.

Straightness and flatness are checked with a precision spirit level, autocollimator, or a granite surface plate plus dial gauge; granite plate grades are 0, 1, 2 and 3, and the reference temperature is 20 °C.

Dial indicators: least count 0.01 mm or 0.001 mm; keep the plunger perpendicular to the measured surface and verify repeatability and calibration status at defined intervals.

GD&T symbols: flatness (parallelogram), position (circle with cross), concentricity (double circle), total runout (arrow with two parallel lines); a feature control frame reads symbol, tolerance, then datum references.

Tapping drill size for metric coarse threads = major diameter − pitch; M10 × 1.5 needs an 8.5 mm drill, M8 × 1.25 needs 6.8 mm.

Hand scraping cycle: coat the reference surface plate or straight edge with Prussian blue, rub the workpiece, and scrape only the marked high spots; a typical machine slideway shows 20–25 spots per 25 mm square, while general flat surfaces need 8–12.

Scraper types: flat, half-round, three-square and bearing scrapers; the edge is honed on an oilstone and a small negative rake is used for cast iron.

Shaft alignment targets for flexible couplings: parallel offset within 0.05 mm and angular misalignment within 0.05 mm per 100 mm; use rim-and-face or reverse-dial methods and correct indicator sag.

Shim correction: parallel offset is corrected by equal shims under both feet; angular error is corrected by shims under one foot equal to (face gap × foot distance from coupling) ÷ coupling diameter.

Heat-shrink fitting: required temperature rise ΔT = interference ÷ (α × d), with α ≈ 11.7 × 10⁻⁶ per °C for steel; never heat a greased bearing above about 120 °C.

File grades and cuts: bastard (rough), second cut and smooth; single-cut files for sharpening and finishing, double-cut for rapid stock removal, and draw filing for a fine straight finish.

Location and drive elements: dowel pins and taper pins locate mating parts after reaming; a square key has width and height about d/4 of the shaft and is sized by shear and crushing of the key.

After assembly, recheck runout with a dial indicator and re-torque foundation or cap bolts in stages, because tightening sequence changes the alignment obtained on the bench.

Gear geometry: module m = d/z in mm; circular pitch p = πm; addendum = m; dedendum = 1.25 m; centre distance = m(z₁ + z₂)/2 for standard full-depth involute gears.

Gear ratio i = n₁/n₂ = z₂/z₁; for a compound train, output speed = input × (product of driving teeth ÷ product of driven teeth).

Belt drives: velocity ratio = D/d for an open drive; a V-belt transmits by wedge action in the groove and needs pre-tension giving about 10–15 mm deflection at mid-span of a 1 m span.

Belt length (open): L = 2C + π(D + d)/2 + (D − d)²/(4C); a crossed belt replaces the last term with (D + d)²/(4C) and reverses the direction of rotation.

Chain drives: keep 1–2% of the span as slack on the slack side, align sprockets within about 0.5 mm, and replace the chain when elongation exceeds roughly 1.5% of pitch.

Screw threads: lead = pitch × number of starts; the effort for a square thread is P = W tan(α + φ) and the screw is self-locking when the friction angle φ exceeds the helix angle α.

Couplings: rigid flange couplings need accurate alignment; flexible types (jaw-spider, grid, gear) tolerate defined misalignment; shear-pin and torque-limiting couplings protect the drive from overload.

Power relationships: P = 2πNT/60 watts, and torque T = 9550 × kW ÷ rpm in N·m; belt or gear ratio changes torque inversely with speed for the same power.

Critical speed: a shaft must run well away from its first critical speed, which rises with stiffness and falls with the square root of the supported mass.

Bearing designation 6205: 6 = deep groove ball bearing, 2 = light series, and bore code 05 → 25 mm; codes 00, 01, 02, 03 give 10, 12, 15 and 17 mm, while codes 04 and above are multiplied by 5.

Basic rating life L10 = (C/P)^p × 10⁶ revolutions, with p = 3 for ball bearings and 10/3 for roller bearings; L10h = L10 × 10⁶ ÷ (60n).

Grease: NLGI consistency numbers 0–6, with 2 the most common; fill only 30–50% of the free space, since over-greasing causes churning and overheating.

Oil viscosity: the ISO VG number equals kinematic viscosity at 40 °C in cSt; a higher viscosity index means less viscosity change with temperature.

Stribeck curve: boundary → mixed → hydrodynamic lubrication; full film formation depends on speed, viscosity and load, expressed by the Sommerfeld number S = (ηN/P)(R/c)².

Lip seals: the lip faces the medium being retained, the garter spring sits on the oil side, shaft hardness should be at least 45 HRC with Ra 0.2–0.8 µm, and roughly half of seal failures trace to shaft finish or misalignment.

Clearance and preload: interference fits reduce internal clearance; controlled preload stiffens a spindle and reduces runout, but excessive preload shortens life through overheating.

Failure modes: fatigue spalling, true brinelling from shock loading, false brinelling from vibration during transport or standstill, smearing from sliding, and discoloration from lubrication starvation.

Mounting rule: heat bearings inductively or in an oil bath to no more than 120 °C and press on the ring being fitted (inner ring onto the shaft); never transmit mounting force through the rolling elements.

Core formulas: hydraulic power (kW) = p (bar) × Q (L/min) ÷ 600; cylinder force F = p × A; piston speed v = Q/A.

The relief valve limits maximum system pressure and is normally set 10–15% above the working pressure; it is a safety/limiting device, not a pressure regulator.

Directional control valves: a 4/3 valve's centre condition (open centre, closed centre, tandem, float) determines pump unloading and actuator locking when the spool is centred; CETOP 3 is the common NG6 subplate pattern.

Flow control: meter-in suits resistive loads, meter-out suits overrunning (negative) loads, and a pressure-compensated flow control valve keeps actuator speed constant as load varies.

Filtration and cleanliness: 10 µm return-line and 3–10 µm pressure-line filters are typical; ISO 4406 code such as 18/16/13 is common for industrial hydraulics, and 70–80% of hydraulic failures are contamination-related.

Accumulators: bladder precharge is set to 70–90% of the minimum working pressure; depressurise before any maintenance and never use oxygen or air in a hydraulic accumulator.

Pneumatics: an FRL unit combines filter, regulator and lubricator; shop air is typically 6 bar; cylinder force equals p × piston area on extension and p × (piston area − rod area) on retraction.

Air quality and leaks: drain traps daily, dry air to the required dew point, and repair leaks promptly because they waste compressor energy and cause pressure drop at the tool.

Hoses and safety: burst pressure should be at least four times the working pressure, respect the minimum bend radius, and never search for a pinhole leak with the hand - hydraulic injection injury is a medical emergency.

Foundation practice: the block should be roughly 1–2 times the machine mass, cured for about 28 days, isolated from the floor slab by a joint, and non-shrink grout is poured only after final alignment.

Precision levels are quoted in mm/m; a 0.02 mm/m level changes reading by one division when one end of a 1000 mm base is raised 0.02 mm.

Levelling sequence: rough-level on wedges or jacks, check the bed longitudinally and transversely, perform a twist test at both ends, then tighten anchor bolts in stages and recheck the bubble after each stage.

ISO 230-1 geometric tests cover straightness, flatness, squareness, parallelism, coaxiality, runout and pitch/lead accuracy; ISO 230-2 covers positioning accuracy and repeatability of numerically controlled axes.

Spindle runout test: insert a test mandrel in the taper and measure with a dial gauge close to the nose and again at 300 mm; typical tolerances are 0.005–0.01 mm at the nose and 0.01–0.02 mm at 300 mm.

Squareness of column to table is measured with a dial gauge on a bracket or a square and indicator, commonly to 0.02 mm per 300 mm.

Backlash test: approach the axis from one direction, zero the indicator, reverse and read; typical CNC axis backlash limit is 0.01–0.02 mm and excess is removed by parameter compensation or mechanical adjustment.

Advanced checks: the telescoping ballbar circular test reveals servo mismatch, backlash and squareness errors, while a laser interferometer measures positioning error and repeatability.

Re-check alignment after 24–48 hours of running and after thermal stabilisation, because thermal growth and grout curing shift the geometry obtained at installation.

Key metrics: availability = MTBF ÷ (MTBF + MTTR); OEE = availability × performance × quality, with 85% regarded as world class.

Maintenance strategies: preventive (time/usage based), predictive (condition based), corrective and breakdown; reliability-centred maintenance selects the strategy from failure consequence and the P–F interval.

Vibration monitoring: overall RMS velocity per ISO 10816/20816; bearing defect frequencies BPFO = (z/2)·f_r·(1 − (d/D)cos θ) and BPFI = (z/2)·f_r·(1 + (d/D)cos θ); envelope/acceleration analysis detects early defects.

Thermography locates loose electrical connections, overloaded drives and bearing overheating; a rise of about 10 K above the established baseline justifies investigation.

Basic electrical checks: insulation resistance at least 1 MΩ (new motors far higher), earth resistance below 1 Ω (up to 5 Ω often accepted), motor current unbalance under 10% and voltage unbalance under 1%.

Oil analysis: viscosity at 40 °C, water content below roughly 200–500 ppm, rising total acid number indicates oxidation, and ISO 4406 particle counts track contaminant ingress.

Root-cause tools: 5-Why, Ishikawa diagram (man, machine, material, method, measurement, environment), FMEA with RPN = severity × occurrence × detection, and Pareto charts for prioritisation.

PM checklist items: lubrication quantity and interval, belt tension, filter pressure drop (change at 0.5–1 bar), fastener torque, coupling alignment, and coolant concentration of 5–10%.

Diagnosis flow: observe noise, heat, leak or alarm; check simple causes (supply, fuse, E-stop, limit switch, interlock); read PLC diagnostic LEDs and I/O status; only then take instrument measurements and compare with baseline.

Plain carbon steel by carbon content: dead mild below 0.15%, mild 0.15–0.3%, medium 0.3–0.6%, high above 0.6%; the eutectoid composition is about 0.8% C, giving fully pearlitic structure.

Bulk heat treatments: annealing (soften, relieve stress, furnace cool), normalising (refine grain, air cool), hardening (austenitise then quench), tempering (restore toughness after hardening).

Case treatments: carburising at about 900–930 °C gives a 0.8–1.2 mm case; nitriding at 500–550 °C in ammonia gives a hard case without quenching and with minimal distortion; induction and flame hardening harden local areas only.

Hardness testing: Brinell (HB) for castings and annealed parts, Rockwell C (HRC) for hardened steel, Vickers (HV) for case depth and thin sections; conversions follow published tables such as ASTM E140.

Common grades: EN8 (0.4% C shafts), EN9 (0.55% C), EN19 (Cr-Mo for gears and shafts), EN31 (about 1% C-Cr bearing steel), HSS M2 for drills and taps, and carbide inserts classified P, M and K.

Cast irons: grey iron has flake graphite and good damping, spheroidal graphite (ductile) iron has nodular graphite and higher strength, white iron contains cementite and is hard and wear resistant.

Non-ferrous alloys: Al 6061-T6 is weldable and machinable, Al 7075 has high strength, brass (Cu-Zn) is free machining, and phosphor bronze is used for bushes and worm wheels.

Tempering colours on polished carbon steel: pale straw about 220 °C, brown about 240 °C, purple about 280 °C and blue about 300 °C, used as an approximate temperature guide for tools.

Distortion and cracking causes: uneven heating, wrong quench severity, sharp section changes and retained austenite; stress-relieve before finish machining and temper immediately after quenching.

Cutting calculations: V = πDN/1000 in m/min, so N = 1000V/(πD) rpm; feed is in mm/rev and the material removal rate for turning is approximately V × f × d.

Taper: tan α = (D − d)/(2L) for the half angle, and taper ratio = (D − d)/L; the compound slide is swivelled through the half angle α.

Trigonometry: sin = opposite/hypotenuse, cos = adjacent/hypotenuse, tan = opposite/adjacent; for a sine bar the stack height h = L sin θ, where L is the roll centre distance.

Electrical power: three-phase P = √3 V I cos φ, single-phase P = V I cos φ; efficiency = output ÷ input; V = IR with series and parallel resistance rules.

Strength of materials: stress σ = F/A, strain ε = ΔL/L, Young's modulus E = σ/ε; torque T = F × r and power P = 2πNT/60.

Thermal expansion: ΔL = α L ΔT, with α about 11.7 × 10⁻⁶ per °C for steel and about 23 × 10⁻⁶ per °C for aluminium.

Mensuration: cylinder volume πr²h, cone volume πr²h/3, sphere volume 4πr³/3, circumference πD; area of a circle πr².

Unit conversions: 1 inch = 25.4 mm, 1 bar = 14.5 psi = 1.02 kgf/cm², 1 kW = 1.341 hp, 1 kgf = 9.81 N.

Percentages and ratios: percentage change = (new − old)/old × 100; a belt or gear ratio multiplies speed by the diameter or tooth ratio and divides torque by the same factor.

Projection convention: first-angle projection (IS/ISO, used in India) places the object between observer and plane, so the front view sits above the top view and the left view appears on the right; third-angle reverses this arrangement.

Section views: the cutting plane is marked A-A, cut material is hatched at 45°, adjacent parts are hatched in opposite directions, and ribs, shafts and fasteners are not hatched when cut longitudinally.

Limits notation: ∅30 H7/g6 denotes a hole with lower deviation zero and a shaft entirely below nominal; capital letters are holes and lower-case letters are shafts in the ISO limits and fits system.

Surface texture symbol: the Ra value in µm sits above the tick, with the machining method, sampling length and lay symbol indicated; roughness grade numbers N1–N12 correspond to standard Ra values.

Feature control frame: read as geometric characteristic symbol, tolerance zone value (with diameter where applicable), then datum references; the datum feature carries a letter in a box with a filled triangle.

Assembly drawings carry balloon numbers that match the parts list or bill of materials giving part number, description, material and quantity per assembly.

Conventional representation: external threads are shown by a thick root line and thin crest line, internal threads by hidden thin lines; springs and gears are drawn schematically rather than as true helices or involutes.

Welding symbols per ISO 2553: arrow line, reference line and symbol, with the leg size to the left of the fillet symbol and the length and pitch to the right.

The title block records material, scale, general tolerance, projection symbol, revision and drawing number; always check the general tolerance note before reading individual dimensions.

Statutory working conditions in India: a maximum of 48 hours per week and 9 hours per day, a rest interval after five hours of continuous work, and overtime limited to 50 hours per quarter, recorded in the statutory register.

Communication standard: the 7 Cs (clear, concise, concrete, correct, coherent, complete, courteous); a fault report states machine number, symptom, time, action taken and current status.

Teamwork tools: 5S (sort, set in order, shine, standardise, sustain) and Kaizen, where small continuous improvements are proposed and implemented by the work team itself.

Time and task management: Eisenhower urgent/important prioritisation, plan–do–check–act cycles for maintenance tasks, and updating the work order in the CMMS before leaving the job.

Digital literacy: professional email with a meaningful subject line, spreadsheet handling of fault and downtime data, and basic password and data-safety discipline.

Career and statutory benefits: resume with measurable achievements, STAR-format interview answers, NSQF/NTC progression routes, and entitlements such as provident fund and ESI where applicable.

Ethics and safety culture: report near misses, never bypass interlocks or guards, and refuse unsafe work while informing the supervisor in writing.

Environmental practice: segregate metal chips, used oil, coolant and e-waste as separate waste streams, and switch off idle machines, lights and compressors to cut energy use.

Cost awareness: an estimate combines material, labour, machine-hour rate and overhead; small workshops also need GST registration and proper invoicing to quote and bill work.