Maharashtra HSC Mechanical Technology (Vocational) cheat sheet

Turning: cutting speed V = πDN/1000 m/min, feed f in mm/rev, depth of cut = (D − d)/2, machining time per pass = L/(f × N).

Taper turning with the compound rest swivelled: tan α = (D − d)/(2L), where α is the half taper angle.

Lathe thread cutting: gear ratio (driver/driven) = pitch of workpiece thread / pitch of lead screw.

Down (climb) milling: cutter rotation is in the same direction as feed, chip thickness starts maximum and falls to zero; needs a backlash eliminator, gives better finish.

Twist drill geometry: standard point angle 118°, helix angle about 30°, chisel edge angle 120–135°; 135° split point for hard or stainless steels.

Shaper stroke length ≈ job length + 20 to 25 mm clearance; quick-return ratio typically 3:2, so the return stroke is faster than the cutting stroke.

Grinding wheel marking A-46-K-5-V: A = aluminium oxide, 46 = grit, K = grade, 5 = structure, V = vitrified bond; softer grades for hard materials.

Single-point tool signature (ASA): back rake, side rake, end relief, side relief, end cutting edge, side cutting edge, nose radius - e.g. 0-7-7-8-15-16-0.8.

Hot-hardness order: HSS (~600 °C) < cemented carbide (~1000 °C) < ceramic < CBN < diamond; diamond is not used on steel because of carbon diffusion.

First-angle projection is the Indian standard: the view obtained from the left is placed on the right of the front view; the truncated-cone symbol identifies the method.

Line precedence: visible outlines > hidden (dashed) lines > centre lines > dimension, extension and leader lines.

Isometric drawing: lengths along the three axes at 30° to the horizontal are 0.816 × true length (isometric scale); isometric projection uses full true length.

Hole basis system in limits and fits (IS 919): hole deviation H with lower deviation zero; shaft letters a–h give clearance, j–n transition, p–zc interference.

IT grades run IT01 to IT16; smaller number = tighter tolerance. IT01–IT5 for gauges, IT6–IT11 for mating fits, IT12–IT16 for rough non-mating work.

Surface roughness Ra is the arithmetic mean deviation of the profile over the sampling length, marked in micrometres on the surface with a tick symbol.

Hatching in sections is thin continuous lines at 45° to the main outlines, equally spaced; shafts, bolts, nuts, keys and pins cut longitudinally are not hatched.

CAD model types: wireframe (edges only), surface (faces, no volume), solid (closed volume giving mass properties); parametric models rebuild from dimensions and constraints.

Layers control colour, line type and visibility; blocks create reusable standard components and keep drawing file size small.

Plain carbon steel by %C: low carbon ≤0.3 (mild steel 0.15–0.25), medium 0.3–0.6, high 0.6–1.4; strength and hardness rise with carbon, ductility and weldability fall.

HSS 18-4-1: about 18% W, 4% Cr, 1% V, 0.7% C; secondary hardening on tempering keeps hardness to roughly 600 °C.

Cast irons: grey (flake graphite, good damping), white (cementite, hard and brittle), malleable (heat-treated white iron), SG/nodular (spheroidal graphite, ductile).

Hardening: heat 30–50 °C above the upper critical temperature, soak, quench in brine, water or oil according to hardenability; temper immediately to remove brittleness.

Case hardening: carburising (0.8–1.1% C skin on low-carbon steel), nitriding (hard skin, no quench, needs alloy steel), cyaniding and induction/flame hardening.

Austenitic stainless steel 18-8 (AISI 304) = 18% Cr, 8% Ni; non-magnetic, corrosion resistant, not hardened by heat treatment, only by cold work.

Non-ferrous alloys: brass = Cu + Zn, bronze = Cu + Sn, duralumin = Al + Cu + Mg + Mn, Babbitt = Sn-Sb-Cu bearing lining alloy.

Iron–carbon diagram: eutectoid 0.8% C at 723 °C gives pearlite; eutectic 4.3% C at about 1130 °C gives ledeburite; austenite is stable above the critical range.

Hardness testing: Brinell (10 mm ball, 3000 kg, HB), Rockwell C (diamond cone, 150 kg), Vickers (diamond pyramid, HV) - Vickers suits thin and case-hardened surfaces.

Vernier least count = 1 main scale division − 1 vernier division; a 49 mm main scale divided into 50 vernier parts gives 0.02 mm.

Micrometer least count = screw pitch / thimble divisions = 0.5 mm / 50 = 0.01 mm; zero error is measured first and applied as a correction to every reading.

Sine bar: sin θ = h/L, with L the roller centre distance (100, 200, 250, 300 mm); accurate only up to about 45° because the sine function changes slowly near 90°.

Slip gauges are wrung together to build a stack; grades 00 and 0 for calibration, grades 1 and 2 for workshop and inspection use.

Taylor's principle: the Go gauge is full-form and checks the maximum material condition; the No-Go gauge checks each element separately at the minimum material condition.

Form tolerances (straightness, flatness, roundness, cylindricity) need no datum; orientation and location tolerances (parallelism, squareness, position, runout) need a datum.

Surface roughness: Ra (arithmetic mean), Rz (ten-point height), RMS; lower value = smoother. Typical values - turning 1.6–6.3 µm, grinding 0.4–1.6 µm, lapping 0.05–0.4 µm.

SPC: X-bar and R charts monitor process mean and variation; Cp = (USL − LSL)/6σ, Cpk includes centring; Six Sigma ≈ 3.4 defects per million opportunities.

Interchangeability requires limits and fits; selective assembly is used where tolerances are too tight for economic manufacture, as in ball bearings.

Metric tapping drill size = major diameter − pitch; M8 × 1.25 needs 6.75 mm (use 6.8 mm), M10 × 1.5 needs 8.5 mm, M12 × 1.75 needs 10.2 mm.

File grades by tooth spacing: rough, bastard, second cut, smooth; single cut for finishing soft metals, double cut for fast removal, rasp for wood and leather.

Hacksaw blade selection: 14 TPI for thick solid sections, 18 TPI general work, 24 TPI for thin tube and sheet; at least three teeth must touch the work.

Chisel types: flat for chipping, cross-cut for keyways, diamond for corners, half-round for oil grooves; cutting angle about 60–70° for mild steel.

Marking-out equipment: surface plate, scriber, dividers, trammel, centre punch (90° point), V-block, angle plate and marking blue.

Reaming removes 0.1–0.3 mm for a close, round hole; boring corrects location; lapping and honing give the finest surface finish and tightest tolerance.

Bench vice: grip the work below the top of the jaws; a file must never be used without a securely fitted handle to prevent hand injury.

Assembly methods: bolted (removable), riveted (permanent), keyed or splined (torque transmission), press and shrink fits (interference), welded (permanent).

Limit calculations: clearance = hole minimum − shaft maximum; interference = shaft minimum − hole maximum; a transition fit may give either depending on actual sizes.

Pattern allowances: shrinkage (cast iron about 10 mm/m, aluminium 13–16 mm/m, steel about 20 mm/m), draft 1–3°, machining 2–5 mm, plus distortion/camber allowance.

Moulding sand properties: green strength, permeability, refractoriness, collapsibility, adhesiveness, flowability; green sand = silica sand + clay binder + water + additives.

Casting defects: blowholes and porosity (gas), shrinkage cavity (inadequate feeding), cold shut and misrun (low pouring temperature), hot tears, sand inclusion, drop.

Forging is hot working above the recrystallisation temperature; open-die (upsetting, drawing out) and closed-die (flash and draft) forging improve grain flow and strength.

Arc welding electrode E60xx indicates about 60 ksi tensile strength; the coating stabilises the arc, shields the weld pool and adds alloying elements.

Oxy-acetylene flames: neutral (O2:C2H2 ≈ 1:1, about 3200 °C) for steel, oxidising (>1) for brass brazing, carburising (<1) for hard facing and high-carbon steel.

Soldering filler melts below 450 °C (tin-lead or lead-free); brazing filler melts above 450 °C (Cu-Zn or Cu-P spelter) and gives a stronger joint.

Sheet metal operations: shearing, blanking, piercing, bending, deep drawing, spinning; bend allowance = (π/180) × bend angle × (R + K·T), and springback must be compensated.

Bulk forming (rolling, extrusion, drawing, forging) keeps volume constant, so A1L1 = A2L2 for the before and after sections.

Pascal's law: pressure applied to a confined fluid is transmitted undiminished in all directions - the basis of hydraulic presses, jacks and intensifiers.

Continuity: A1V1 = A2V2; cylinder force F = p × A; piston speed v = Q/A; pump delivery Q = displacement × speed.

Circuit valves: pressure relief (safety), pressure reducing, flow control (speed), directional control (4/2, 4/3), check, sequence and unloading valves.

DCV centre positions: open centre unloads the pump, tandem unloads the pump while holding actuators, closed centre blocks all ports, float centre lets the actuator move freely.

Pneumatic FRL unit: filter removes water and dirt, regulator sets line pressure (commonly about 6 bar), lubricator supplies oil mist; meter-out control is preferred because air is compressible.

Hydraulic oil: ISO VG 32/46/68 viscosity grades; contamination causes most hydraulic failures, so filters, breathers and clean flushing are critical.

Accumulator stores pressurised fluid for peak flow or emergency; intensifier raises pressure while reducing flow; gear pumps are cheap, vane pumps balanced, piston pumps for high pressure.

Meter-in controls extending speed under light loads; meter-out is used for overrunning loads; bleed-off is efficient but less precise for varying loads.

Maintenance types: breakdown/corrective (after failure), preventive (scheduled), predictive or condition-based (on measured trend), and proactive (root-cause elimination).

Availability = MTBF / (MTBF + MTTR); availability improves by raising mean time between failures or cutting mean time to repair.

Condition-monitoring techniques: vibration analysis, lubricant and wear-debris analysis, thermography, ultrasonic leak detection, motor current signature analysis.

Lubrication: grease for slow, heavily loaded or sealed bearings; oil for high speed and heat removal; over-greasing (above about one-third of housing free space) causes overheating.

Bearing designation 6205: 6 = deep-groove ball bearing, 2 = light series, 05 = bore 5 × 5 = 25 mm; suffix letters denote seals and clearance.

Alignment: pulleys checked with a straight edge, couplings with dial gauge or feeler; misalignment shows up as vibration at 1× and 2× running speed.

Bolt tightening: use a calibrated torque wrench, follow the manufacturer's torque, and tighten flanges in a diagonal or criss-cross sequence to give even preload.

V-belt drives: tension set by the deflection rule (about 16 mm per metre of span), belts in a set must be matched, never mix worn and new belts.

Fire classes: A solids, B flammable liquids, C flammable gases, D reactive metals, E electrical. Water or CO2 for A, foam or dry powder for B, dry powder for C and D, CO2 or dry powder for E.

Safety colour code (IS): red for fire fighting equipment, green for safety and first aid, yellow for caution and warning, blue for mandatory signs, black/white for information.

Machine shop PPE: safety shoes, close-fitting clothing, goggles or face shield, ear plugs above 85 dBA; gloves are not worn near rotating spindles or drills.

Electrical protection: earthing for fault current, MCB for overload and short circuit, ELCB/RCCB of 30 mA sensitivity for personal shock protection, double-insulated portable tools.

LOTO procedure: isolate the energy source, lock and tag, release stored energy (springs, hydraulics, gravity), verify zero energy, then work; remove only by the person who applied it.

Machine guarding: fixed guards for belts, gears and shafts, interlocked guards on access doors, emergency stop within operator reach, never bypass a guard without a permit.

5S housekeeping: sort, set in order, shine, standardise, sustain; keep aisles and exits clear, clean oil spills immediately, segregate waste.

Noise limit is 90 dBA for an eight-hour exposure; hearing protection is required above 85 dBA; welding fumes and grinding dust need local exhaust ventilation.

Production planning and control functions: routing (sequence of operations), scheduling (timing), dispatching (releasing work) and follow-up (progress chasing).

Cost build-up: prime cost = direct material + direct labour + direct expenses; factory cost adds factory overheads; total cost adds office, selling and distribution overheads.

Break-even quantity = fixed cost / (selling price per unit − variable cost per unit); margin of safety = (actual sales − break-even sales) / actual sales.

Economic order quantity EOQ = √(2DS/H), where D = annual demand, S = ordering cost per order, H = holding cost per unit per year.

Turning time = L/(f × N) minutes; machining cost per piece = machining time × (machine hour rate + labour rate) + tool cost per piece.

Incentive plans: Halsey bonus = 50% of time saved × rate; Rowan bonus = (time saved / time allowed) × time taken × rate; Taylor differential piece rate penalises below-standard output.

Depreciation: straight line = (cost − salvage value) / life per year; sinking fund and declining balance methods charge more in early years.

PERT/CPM: the critical path has zero float and fixes project duration; crashing shortens it by adding resources at extra cost.

Batch production suits medium volumes with setups; mass production uses line balancing and special-purpose machines to reduce unit cost.

Business plan contents: product or service, market analysis, technical feasibility, financial projections, organisation and manpower, risk assessment and exit strategy.

Ownership forms: sole proprietorship (unlimited liability), partnership, LLP (limited liability with lighter compliance), private limited company (separate legal entity, shares).

Udyam (MSME) registration uses both investment and turnover: micro up to ₹1 crore / ₹5 crore, small ₹10 crore / ₹50 crore, medium ₹50 crore / ₹250 crore (2020 limits, revised upward later).

Funding sources: own equity, bank term loan for machinery, working capital limit, MUDRA loans for micro units, PMEGP subsidy, angel or venture capital for scalable ventures.

Working capital cycle = raw material + work in progress + finished goods + receivables − payables; shortening the cycle releases cash for operations.

GST registration is compulsory above the threshold turnover (₹40 lakh for goods, ₹20 lakh for services in most states); the composition scheme suits small turnover.

Intellectual property terms: patent 20 years, trademark 10 years renewable indefinitely, copyright life of the author plus 60 years, registered design 15 years.

SWOT analysis: strengths and weaknesses are internal, opportunities and threats are external; it supports feasibility study and strategy formulation.

Marketing mix (4P): product, price, place and promotion; pricing decisions are supported by costing and break-even analysis.