Maharashtra SSC Mechanical Technology Pre-Voc/NSQF cheat sheet

Personal protective equipment by hazard: safety goggles for grinding and chipping, face shield over goggles for heavy grinding, leather apron and gauntlets for welding, ear plugs above roughly 85 dB, safety shoes in all machine shops.

Fire classes and extinguishers: Class A solid combustibles use water or foam; Class B flammable liquids use foam, dry powder or CO2; Class C electrical use CO2 or dry powder only, never water; Class D metal fires use dry sand or special powder.

Machine guarding rule: no operation with guards removed; chuck key must be removed from the lathe chuck before starting the spindle; never leave a running machine unattended.

Grinding wheel safety: wheel rated speed must equal or exceed machine spindle speed; ring test by light tapping before mounting; tool rest gap kept within about 3 mm of the wheel face.

First aid for electrical shock: switch off supply first or use an insulated object to separate the victim; then check breathing and start CPR if trained; report and record the incident.

Housekeeping and discipline: keep aisles and walkways clear, store oily rags in covered metal bins, never block fire exits, return tools to marked places after use.

Welding-specific hazards: arc eye from ultraviolet radiation, fume extraction for galvanised and painted metal, fire watch for 30 minutes after hot work, flashback arrestors on gas lines.

Hand tool safety rules: carry tools with points and edges downward, never use a file without a handle, cut away from the body, and never strike a hardened tool with a hammer.

Plain carbon steel classification by carbon content: low carbon (mild steel) up to about 0.3% C, medium carbon 0.3-0.6% C, high carbon 0.6-1.4% C; hardness and strength rise with carbon, ductility and weldability fall.

Cast iron types: grey cast iron has flake graphite and good damping and machinability; white cast iron has cementite and is hard and brittle; malleable iron is white iron heat-treated to form temper carbon nodules.

Alloy steel elements: nickel improves toughness, chromium improves corrosion resistance and hardenability, molybdenum improves high-temperature strength, manganese improves hardenability and deoxidises, vanadium refines grain.

Non-ferrous metals: aluminium is light, corrosion resistant and a good conductor; copper has high electrical and thermal conductivity; brass is copper-zinc; bronze is copper-tin; zinc is used for galvanising.

Heat treatment of steel: annealing softens and relieves stress by slow cooling; normalising refines grain by air cooling; hardening requires quenching above the critical temperature; tempering follows hardening to reduce brittleness.

Case hardening and surface hardening: carburising adds carbon to the surface of low-carbon steel, nitriding adds nitrogen, induction and flame hardening harden only the surface layer.

Iron-carbon critical temperature: the lower critical temperature is about 723 degrees Celsius for steel, above which austenite forms; quenching from above this temperature produces martensite.

Material tests: Brinell and Rockwell measure hardness, Vickers uses a diamond pyramid, tensile test gives yield strength and elongation, Izod and Charpy tests measure impact toughness.

Vernier calliper least count = smallest main scale division / number of vernier divisions; for a 1 mm main scale with 50 vernier divisions, least count = 0.02 mm.

Micrometer least count = pitch of screw / number of circular scale divisions; a 0.5 mm pitch screw with a 50-division thimble gives 0.01 mm.

Vernier height gauge measures height above a surface plate; vernier depth gauge measures depth; combination set includes a rule, protractor head, square head and centre head.

Try square checks squareness and flatness of adjacent faces; bevel protractor measures angles to 5 minutes with a vernier; feeler gauge measures gap widths with a set of thin blades.

Surface plate is the reference datum for marking and inspection; it must be kept clean and lightly oiled; blueing (marking medium) is applied before scribing layout lines.

Files are classified by cut (single, double, rasp) and coarseness (rough, bastard, second cut, smooth); file length is measured excluding the tang; clean with a file card.

Hacksaw blade selection: 14 teeth per inch for thick sections, 18 for general work, 24 or 32 for thin tube and sheet; at least three teeth must be in contact with the work.

Chisels: flat chisel for general chipping, cross-cut chisel for keyways, half-round or diamond point for oil grooves; cutting angle for mild steel is about 60-70 degrees.

Filing sequence: select file by shape and cut, clamp work just above jaw height, file with full strokes at about 30 strokes per minute, cross-file then draw-file for finish.

Flatness check by marking medium: coat the surface, rub on a surface plate, and high spots show as bright spots to be filed down; repeat until even contact.

Sawing technique: start with a light forward stroke to make a nick, use full blade length, apply pressure on forward stroke only, and release pressure on return.

Chipping safety and method: wear goggles, chip toward a solid support not toward the vice screw, and use a guard screen when chipping near others.

Drilling layout: centre punch the intersection of scribed lines, then enlarge with a pilot drill; centre punch mark prevents drill wander on flat surfaces.

Fits and tolerances: clearance fit always has a gap, interference fit always has overlap, transition fit may have either; allowance is the intentional difference between mating sizes.

Limits: upper and lower limits define the maximum and minimum permitted sizes; tolerance is the difference between them; nominal size is the reference size on the drawing.

Scraping and lapping: scraping removes high spots with a hand scraper for bearing surfaces; lapping uses abrasive paste between the work and a lap for very fine finish and accuracy.

Drill speed formula: cutting speed V = pi x D x N / 1000, where D is drill diameter in mm and N is spindle speed in rpm; solve N = 1000V / (pi x D).

Tap drill size for metric threads: tap drill diameter = major diameter minus pitch; for M10 x 1.5 the tap drill is 8.5 mm.

Drilling feed and coolant: use lower speed and generous coolant for deep holes, withdraw the drill to clear chips, and use a centre drill first for accurate location.

Tapping procedure: drill tap drill size, countersink the hole, start the tap square with a tap wrench, apply cutting oil, and reverse a quarter turn every half turn to break chips.

Tap types: taper tap starts the thread and is easiest to start, plug tap cuts to near the bottom, bottoming tap finishes threads in blind holes.

Die and stock: used for cutting external threads; the die is started square on a chamfered rod, oiled, and turned back a quarter turn periodically to break chips.

Thread designation: M10 x 1.5 means metric thread, 10 mm major diameter, 1.5 mm pitch; a fine series thread has a smaller pitch than the coarse series for the same diameter.

Reaming and counterboring: reaming finishes a drilled hole to accurate size with a reamer; counterboring enlarges the top of a hole for a socket head screw; countersinking produces a conical seat for a flat head screw.

Lathe parts: bed, headstock with spindle, tailstock for supporting long work or holding drills, carriage with saddle, cross-slide, compound rest and tool post.

Turning speed: N = 1000V / (pi x D) with V in m/min; for mild steel with high-speed steel tool use about 30 m/min, so a 50 mm bar runs near 190 rpm.

Feed is the tool advance per revolution in mm/rev; depth of cut is half the difference between the initial and final diameter on a plain turning cut.

Lathe operations: facing produces a flat end, plain turning reduces diameter, taper turning uses compound rest swivel or tailstock offset, knurling forms a grip pattern, boring enlarges an internal hole.

Thread cutting on a lathe requires the half-nut engaged with the lead screw at the correct gear ratio so the tool follows the thread pitch; the thread dial indicates when to engage.

Taper calculation: taper = (D - d) / L; for tailstock offset method, offset = (D - d) x length of job / (2 x taper length).

Chuck safety: three-jaw self-centring chuck for round and hexagonal work, four-jaw independent chuck for irregular work and heavy jobs; remove the chuck key before starting.

Tool geometry: rake angle affects cutting force and chip flow, clearance angle prevents rubbing, nose radius improves surface finish; positive rake suits soft ductile metals.

Arc welding: electrode holder and work return cable complete the circuit; electrode coating provides shielding gas and slag; straight polarity (electrode negative) gives more penetration on thin work; reverse polarity (electrode positive) suits thicker work.

Arc welding current rule of thumb: current in amperes roughly 30 to 40 times electrode diameter in mm for a general-purpose electrode; adjust for position and thickness.

Gas welding flames: neutral flame has equal oxygen and acetylene and suits steel; oxidising flame has excess oxygen and suits brass; carburising flame has excess acetylene and is used for case hardening and aluminium.

Oxy-acetylene safety: never use oil or grease on oxygen fittings, open the acetylene valve no more than one and a half turns, use a flashback arrestor, and keep cylinders upright and secured.

Brazing joins metals with a filler melting above 450 degrees Celsius but below the parent metal melting point; soldering uses filler melting below 450 degrees Celsius.

Brazing and soldering need flux to remove oxide and prevent reoxidation; zinc chloride is a common flux for soldering, borax for brazing; clean flux residue after the joint.

Weld defects: porosity from gas trapped in the metal, slag inclusion from poor cleaning between passes, undercut from excessive current, lack of penetration from insufficient current or poor root gap.

Resistance welding: spot welding passes current through the work between copper electrodes; heat depends on current squared times resistance times time, so current is the dominant factor.

First-angle projection: the object is placed between observer and plane, so the top view is drawn below the front view and the left side view to the right of the front view.

Third-angle projection: the plane is between observer and object, so the top view is drawn above the front view and the right side view to the right; the symbol shows a truncated cone.

Line types: continuous thick for visible outlines, continuous thin for dimension and projection lines, dashed for hidden edges, chain thin for centre lines and cutting plane lines.

Dimensioning rules: dimensions are placed on views showing true shape, never duplicated, and given in millimetres without the unit symbol; dimension lines are drawn parallel to the measured edge.

Scale: drawing scale is drawing length divided by actual length; 1:1 is full size, 1:2 is half size, 2:1 is double size; always state the scale in the title block.

Section views: hatching lines at 45 degrees show cut material, adjacent parts are hatched in opposite directions, and a cutting plane line with arrows shows the viewing direction.

Isometric sketching: the three axes are 120 degrees apart, vertical edges stay vertical, and all measurements along the axes are drawn to the same scale without foreshortening.

Tolerance and fits on drawings: a dimension such as 25 +0.05/-0.00 gives the upper and lower limits; geometric symbols such as flatness and perpendicularity control form and orientation.

Electrical supply in Indian workshops is typically 230 V single phase and 415 V three phase at 50 Hz; three-phase motors use three live wires plus earth.

Motor starters: direct-on-line starter suits small motors, star-delta starter reduces starting current to about one third, and a soft starter ramps voltage to limit inrush current.

Earthing is essential: the equipment body is connected to earth so a fault current trips the protective device; earth wire is green or green-yellow and never used as a live conductor.

Fuses and MCBs protect against overload and short circuit; an MCB can be reset while a fuse must be replaced; the rating must match the circuit conductor and load.

Compressed air: workshop air is generated by a compressor and stored in a receiver; a pressure regulator and filter unit supplies clean air at the required pressure to tools.

Hydraulic power: a pump supplies oil to cylinders and motors; pressure relief valve protects the system, and pressure equals force divided by piston area.

Welding power sources: constant-current characteristic suits shielded metal arc welding, constant-voltage suits gas metal arc welding; alternating current sources use a transformer, direct current sources use a rectifier or generator.

Machine nameplate data: rated voltage, frequency, current, power and duty cycle must be checked before connecting a machine; a motor rated for continuous duty should not be run beyond its rating.

Thread standards: metric threads are specified by major diameter and pitch (M12 x 1.75); unified threads use threads per inch (1/2-13 UNC); BSW uses inch sizes with Whitworth form.

Bolt and screw distinction: a bolt is used with a nut and passes through clearance holes, a screw threads into one of the parts; a stud is threaded at both ends and used with a nut.

Washers: plain washers spread load under the head, spring washers maintain tension and resist loosening, and taper washers correct for sloped surfaces.

Keys and keyways transmit torque between a shaft and a hub; a Woodruff key sits in a semicircular seat, a parallel key in a machined slot, a taper key is driven in for a tight fit.

Rivets: a rivet is a permanent fastener; the shank is inserted through the hole and the tail is upset to form a head; rivet diameter is usually about twice the plate thickness.

Locking devices: split pin through a castle nut, tab washer, nylon insert lock nut, thread-locking fluid, and stake or peen methods all resist vibration loosening.

Assembly torque and sequence: use a torque wrench to the specified value and tighten bolts in a diagonal or star pattern for flanged joints to avoid distortion.

Pins and circlips: dowel pins locate parts accurately, taper pins lock and transmit light torque, and circlips retain components in grooves on shafts or bores.

Preventive maintenance is scheduled work to prevent breakdown; breakdown maintenance is repair after failure; predictive maintenance uses condition data such as vibration and temperature.

Lubrication: grease for slow, heavily loaded bearings and oil for high-speed bearings; over-greasing can damage seals, and the correct grade is specified by the machine manual.

Wear checks: check belt tension and alignment, chain slack, bearing temperature and noise, oil level and condition, and coolant concentration at planned intervals.

Inspection instruments: a micrometer measures external diameters, a bore gauge measures internal diameters, a dial indicator measures runout and alignment, and a surface roughness tester measures Ra.

Quality control basics: accuracy is closeness to the true value, precision is repeatability of readings; calibration against a standard traceable to a national standard is required.

Seven basic quality tools include check sheet, histogram, Pareto chart, cause-and-effect diagram, control chart, scatter diagram and flowchart; Pareto analysis focuses on the few largest causes.

Sampling: 100 percent inspection checks every item, sampling inspects a lot and infers quality; acceptance sampling uses an AQL and a sampling plan with accept and reject numbers.

Records and traceability: log inspection results, keep calibration records with dates and standards used, and mark rejected parts clearly to prevent mixing with accepted stock.

NSQF levels run from 1 to 10; the SSC vocational courses map to a specified level, and each qualification states its level, credit and job role in the qualification pack.

Communication process: sender, message, channel, receiver and feedback; feedback confirms understanding, and noise is any interference that distorts the message.

Workplace documents: job card records work done, inspection report records measured results, material requisition requests stores issue, and incident report records accidents.

Report writing structure: purpose, facts observed, action taken, recommendation, date and signature; keep it objective and free of personal blame.

Teamwork and behaviour: follow the chain of command, report hazards immediately, respect gender and cultural diversity, and avoid harassment; grievances go through the stated procedure.

Safety and rights at work: an employee has the right to a safe workplace and to refuse unsafe work; personal responsibility includes using PPE and reporting near misses.

Digital and financial basics: use email with a clear subject line and short paragraphs, keep passwords confidential, and understand minimum wages, deductions and payslip components.

Interview and self-presentation: research the employer, prepare examples of skills used, dress appropriately, arrive early, and ask relevant questions about the role.

NSQF levels run from 1 to 10; each qualification pack states its level, credits and job role, and the SSC vocational course maps to a specified level.

Communication process: sender, message, channel, receiver and feedback; feedback confirms understanding, and noise is any interference that distorts the message.

Workplace documents: job card records work done, inspection report records measured results, material requisition requests stores issue, and incident report records accidents.

Report writing structure: purpose, facts observed, action taken, recommendation, date and signature; keep it objective and free of personal blame.

Teamwork and behaviour: follow the chain of command, report hazards immediately, respect gender and cultural diversity, and avoid harassment; grievances go through the stated procedure.

Safety and rights at work: an employee has the right to a safe workplace and to refuse unsafe work; personal responsibility includes using PPE and reporting near misses.

Digital and financial basics: use email with a clear subject line and short paragraphs, keep passwords confidential, and understand minimum wages, deductions and payslip components.

Interview and self-presentation: research the employer, prepare examples of skills used, dress appropriately, arrive early, and ask relevant questions about the role.