MSCE Metalwork cheat sheet

Duty of care hierarchy: eliminate the hazard, substitute, engineer controls, administrative controls, then PPE as the last line of defence.

Fire classes and extinguishers: Class A (solids) water; Class B (flammable liquids) foam/CO2; Class C (gases) dry powder; electrical fires CO2 or dry powder, never water; Class D (metals such as magnesium) dry powder only.

Hot work permit requires a 10 m clear zone of combustibles, a fire watch during work and at least 30 minutes after, and gas cylinders secured upright.

Oxy-acetylene cylinder spacing: fuel gas and oxygen cylinders stored at least 3 m apart, or separated by a fire-resistant barrier at least 1.5 m high.

Acetylene must never be used above 1.5 bar (approx 15 psi) working pressure; free acetylene is unstable above about 1 bar.

Electrical isolation follows lock-out/tag-out: isolate, lock, tag, prove dead with a tested instrument, then work.

LEV (local exhaust ventilation) controls welding fume and grinding dust at source; respiratory protection is supplementary, not a substitute.

Noise action values: 80 dB(A) lower exposure action value, 85 dB(A) upper exposure action value requiring hearing protection and hearing checks.

Manual handling risk assessment uses TILE: Task, Individual, Load, Environment.

Plain carbon steel carbon ranges: low carbon (mild) up to 0.3% C, medium carbon 0.3–0.6% C, high carbon 0.6–1.4% C.

Cast iron contains 2–4% C; above roughly 2% C the Fe-C system forms cast structures rather than wrought steels.

Stainless steel 304 (18/8) is austenitic, non-magnetic when annealed, and resists corrosion via a chromium oxide passive layer (minimum ~10.5% Cr).

Aluminium alloys: 1000 series pure, 2000 Cu (high strength, poor corrosion), 5000 Mg (marine, weldable), 6000 Mg+Si (extrudable, heat-treatable), 7000 Zn (highest strength).

Copper is an excellent electrical and thermal conductor; brass is Cu-Zn and bronze is Cu-Sn (or Cu-Al for aluminium bronze).

Tensile strength = maximum load / original cross-sectional area; yield strength marks the onset of permanent deformation.

Hardness scales are not interchangeable; convert only via published tables, and Brinell uses a hardened ball, Rockwell a cone or ball.

Ductile materials show significant elongation before fracture; brittle materials fail with little deformation, so notch toughness matters for impact loads.

Galvanic corrosion occurs where dissimilar metals contact in the presence of an electrolyte; separate them or choose a compatible pair.

Cold chisel cutting angles: about 60° for mild steel, 70° for cast iron, 30–40° for aluminium and copper.

Hacksaw blade selection: 14–18 TPI for thick sections and soft metals, 24–32 TPI for thin tube, sheet and hard metals.

Files cut on the forward stroke only; pressure is applied on the push and released on the return to preserve the teeth.

File grades: rough, bastard, second cut, smooth; double-cut files remove material faster, single-cut files give finer finishes.

A tap wrench, die stock, and correct pilot drill are required; never use pliers in place of a properly sized wrench on fasteners.

Snips: straight-cut for sheet edges, aviation (compound-lever) snips for curves, notching snips for internal cuts.

Punch types: centre punch for layout marks, prick punch for fine location, pin punch for driving out pins, taper punch for alignment.

A scriber should be harder than the workpiece and used with a rule or square; layout dye improves visibility on bright metal.

Spanners must fit the fastener flats fully; adjustable wrenches should be pulled toward the fixed jaw to avoid slipping.

Vernier caliper reading = main scale value + (coinciding vernier division × least count); a 0.02 mm vernier has 50 divisions on 49 mm.

Micrometer reading = barrel scale + thimble reading; a 0.01 mm metric micrometer has 50 thimble divisions for 0.5 mm spindle travel.

Zero error: check anvils closed; positive error is subtracted, negative error is added to the reading.

Vernier height gauges and depth gauges use the same least-count logic as calipers; always reference from a machined surface.

Engineer's blue (marking out dye) is applied thinly so scribed lines show clearly without obscuring the surface.

Datum selection: choose a machined face as the primary datum and reference all dimensions from it to avoid tolerance stack-up.

Odd-leg (Jenny) calipers transfer and bisect distances; dividers scribe arcs and circles; hermaphrodite calipers mark parallel lines from an edge.

A dial test indicator measures small deviations and runout; it is a comparator, not an absolute measuring instrument.

Allowance for cutting: mark the cut line on the waste side of the scribed line, leaving the line intact on the finished part.

Drilling speed formula: N (rpm) = (1000 × cutting speed in m/min) / (π × drill diameter in mm).

Tap drill size for metric coarse threads ≈ major diameter − pitch (e.g. M8 × 1.25 → 6.75 mm, nearest 6.8 mm).

Tapping sequence: tap drill, countersink or centre, taper tap, intermediate tap, plug/bottoming tap, with cutting fluid and quarter-turn backing off.

Drilling feeds: high speed steel drills cut mild steel at roughly 25–30 m/min; aluminium at 60–100 m/min; use coolant on steel.

Filing technique: cross-filing for flatness, draw-filing for finish, and checking with a straight edge or engineer's square against light.

Hacksawing: long steady strokes using most of the blade, light pressure on start and finish, and the blade set with teeth pointing forward.

Reaming removes 0.1–0.3 mm from a drilled hole to improve size and surface finish; reamers must not be rotated backwards.

Fits: clearance fit always has a gap, interference fit always has overlap, transition fit may give either; H7/h6 is a common location clearance fit.

Deburring after drilling and sawing prevents stress raisers and injury; a countersink or hand scraper removes the burr.

Soldering operates below 450 °C; brazing operates above 450 °C but below the melting point of the parent metals.

Soft solder is typically tin-lead or lead-free tin-copper/tin-silver; flux removes oxide and must match the parent metal (rosin for electronics, zinc chloride for sheet metal).

Brazing filler metals: copper-zinc (spelter) around 870–900 °C, silver solder (Cu-P-Ag) around 600–700 °C; capillary action draws filler into a close joint gap of 0.05–0.2 mm.

Riveted joint types: lap joint and butt joint with single or double strap; rivet diameter for sheet is commonly about twice sheet thickness.

Rivet hole clearance is typically 1.5–2 mm larger than rivet diameter for hot riveting; cold riveting uses tighter holes.

Pop (blind) rivets are set by mandrel tension and are not structural unless specified as such; check grip range before use.

Thread standards: metric coarse is the default; fine pitch is used for thin walls, vibration resistance and fine adjustment.

Torque tightening should follow a sequence (star or spiral) and use a calibrated torque wrench; thread lubricant changes the achieved preload.

Bolted joints should use washers under nuts and heads, and locking methods (nyloc, spring washer, threadlocker) where vibration is present.

MMA (SMAW) uses a consumable coated electrode; the coating provides shielding gas and slag, so polarity and electrode type must match the specification.

MIG (GMAW) uses a continuous wire electrode with an inert or active shielding gas; short-circuit transfer suits thin sheet, spray transfer suits thicker sections.

TIG (GTAW) uses a non-consumable tungsten electrode with separate filler and argon shielding; it suits thin sheet, stainless and aluminium.

Oxy-acetylene flame types: neutral (1:1 ratio) for steel, oxidising (excess oxygen) for brass, carburising (excess acetylene) for high-carbon steel.

Oxy-acetylene cutting preheats steel to about 870 °C (bright cherry red) before the oxygen jet starts the cut; it does not cut cast iron or most non-ferrous metals effectively.

Weld defects: porosity from gas entrapment, lack of fusion from low heat input, undercut from excessive current or travel speed, slag inclusion from poor inter-run cleaning.

Distortion control: balanced welding sequence, back-step welding, jigs and fixtures, pre-setting, and stress-relieving after welding.

Current selection for MMA is roughly 30–40 A per mm of electrode diameter; a 3.2 mm electrode runs around 100–130 A.

Post-weld heat treatment relieves residual stress; it is essential for thick sections and some alloy steels before machining.

Bend allowance BA = θ × (π/180) × (R + K × T), where θ is bend angle in degrees, R inside radius, T thickness and K the neutral-axis factor (commonly 0.33–0.5).

Bend deduction = 2 × outside setback − bend allowance; flat length = sum of outside dimensions − bend deductions.

Minimum bend radius depends on material and temper; 1T is typical for soft aluminium, 1–2T for mild steel, and larger for hard tempers.

Sheet gauges are not linear; always convert the gauge number to millimetres using the specific standard (e.g. zinc gauge, US standard gauge).

Rolling: sheet is passed through rolls to form cylinders; the ends remain flat until pre-bent, so allow for end correction.

Notching and corner relief prevent tearing when folding a box; relief radius should be at least the material thickness.

Sheet metal shear capacity is limited by thickness and material shear strength; keep fingers clear and use a hold-down.

Seam types: folded lock seam, grooved seam, and Pittsburgh lock for ductwork; riveted or spot-welded seams are used where a rigid joint is needed.

Development of a truncated cone or transition piece uses radial line or triangulation methods; accuracy depends on true-length lines.

Forging temperature for mild steel is roughly 1100–1250 °C (bright yellow-white); stop forging below about 900 °C to avoid cracking.

Annealing: heat above the critical temperature, hold, then cool very slowly (furnace cool) to soften and relieve stress.

Normalising: heat above the critical temperature then cool in still air; refines grain structure and improves machinability.

Hardening: heat to the austenitising temperature and quench (water for carbon steel, oil for alloy steel); hardness depends on carbon content and cooling rate.

Tempering follows hardening: reheat below the critical range (typically 150–650 °C) to trade hardness for toughness.

Case hardening (carburising) adds carbon to the surface of low-carbon steel, giving a hard wear-resistant skin with a tough core.

Critical temperatures: lower critical (A1) around 723 °C for plain carbon steel; upper critical (A3) varies with carbon content.

Hot working is above the recrystallisation temperature; cold working causes work hardening, which can be removed by annealing.

Forging operations: upsetting (reduces height, increases diameter), drawing down (reduces section, increases length), swaging, and punching.

Cutting speed formula: V (m/min) = (π × D × N) / 1000, where D is diameter in mm and N is spindle speed in rpm.

Turning: feed is in mm/rev, depth of cut is radial, and cutting speed depends on tool material - HSS around 25–40 m/min in mild steel, carbide 150–300 m/min.

Lathe operations: facing, turning, boring, parting off, knurling, thread cutting; the compound slide is set to half the included angle for taper turning.

Milling: climb milling gives better finish and longer tool life on rigid machines with backlash eliminators; conventional milling is safer on older machines.

Drilling on a pedestal drill: clamp the work, use a centre drill first, and reduce spindle speed for large diameters.

Surface finish improves with higher speed, lower feed, and a sharp tool with correct nose radius; chatter indicates insufficient rigidity.

Tool geometry: rake angle affects cutting force and chip flow; clearance angle prevents rubbing; too much rake weakens the edge.

Speeds and feeds must be reduced when using coolant interruption, interrupted cuts, or machining hard or work-hardening materials.

Grinding uses abrasive wheels; wheel hardness, grit size and bond must suit the material, and wheel guards must be in place.

First-angle projection: the view from the front is placed above the plan, and the left view appears on the right; third-angle projection reverses this.

Orthographic views: front, plan (top), and end elevation; hidden detail is shown with dashed lines and centrelines with chain-dotted lines.

Dimensioning rules: give each dimension once, dimension to visible features, avoid dimensioning to hidden lines, and state units once in the title block.

Tolerance notation: limit dimensions show maximum and minimum sizes; bilateral tolerance is ±, unilateral is one direction only.

Geometric tolerancing symbols: flatness, straightness, roundness, cylindricity, parallelism, perpendicularity, angularity, position, concentricity, runout.

Surface finish Ra is the arithmetic mean roughness; lower Ra values indicate a smoother surface, and the triangle symbol indicates the required finish.

Section views use hatching at 45°; adjacent parts are hatched in opposite directions, and standard parts such as bolts are not sectioned.

Scale drawing: a scale of 1:2 halves the drawing, 2:1 doubles it; always state the scale in the title block.

Project planning: a cutting list and operation sequence reduce waste; identify datum, stock size, allowances, and inspection points before starting.