NSSCO Metalwork and Welding 6188 cheat sheet

Arc welding requires a helmet with shade 10–13, leather gauntlets, a flame-retardant apron, safety boots and fume protection; gas welding goggles use shade 3–6.

Acetylene cylinders must stand upright and be secured; fit flashback arrestors at the regulator and torch, and never exceed about 1 bar (15 psi) acetylene delivery pressure.

Hose colour code: oxygen is blue or black and acetylene is red; test for leaks with soapy water, never with a flame.

Fire classes: A solids, B flammable liquids, C gases, D metals, E electrical; water suits class A, foam or CO2 suits B, dry powder suits C, special powder suits D and CO2 suits electrical fires.

Welding stainless steel can release hexavalent chromium and nickel fume; welding galvanised steel releases zinc oxide fume; both need local exhaust ventilation and respiratory protection.

The noise action level is 85 dB(A) over an 8-hour day; hearing protection is required above this level and when using pedestal grinders or chipping hammers.

Burn first aid: cool under running water for at least 20 minutes, remove jewellery, and cover with a sterile non-stick dressing; do not apply butter, oil or ice.

Oily rags and mixed metal swarf can self-heat; store them in a closed metal container and clear combustible waste daily.

Plain carbon steel contains 0.05–2.1% carbon; cast iron contains about 2–4% carbon and is brittle in tension.

Mild steel (0.15–0.30% C) has a tensile strength near 400–500 MPa, is ductile and welds readily; high-carbon steel (>0.6% C) is harder and more prone to cracking on welding.

Stainless steel contains at least 10.5% chromium, which forms a passive oxide layer; grade 304 is about 18% Cr and 8% Ni, and grade 316 adds molybdenum for chloride resistance.

Aluminium has a density near 2.7 g/cm³, about one-third that of steel; it forms a tough oxide layer, has no true endurance limit and is TIG welded with AC after oxide removal.

Copper conducts heat and electricity well; brass is copper-zinc, bronze is copper-tin, and both resist corrosion better than plain steel.

Strength resists load, hardness resists indentation, ductility allows wire drawing, malleability allows hammering into sheet, toughness absorbs impact and elasticity allows recovery of shape.

Spark test: mild steel gives long white sparks with few bursts, high-carbon steel gives short bright bushy sparks, and cast iron gives short red sparks.

Galvanised sheet has a zinc coating; grind it back at least 25 mm from a weld joint and ventilate, because zinc oxide fume causes metal fume fever.

A steel rule reads to 0.5 mm, a vernier caliper has a least count of 0.02 mm, and an outside micrometer has a least count of 0.01 mm.

Vernier reading = main scale value + (coinciding vernier division × least count).

Micrometer reading = barrel reading + (thimble division × 0.01 mm); check zero with the anvils closed and use the ratchet stop.

A try square checks 90°, a combination square gives 90° and 45°, and a bevel protractor measures angles in degrees and minutes.

Mark out from a datum face using a scriber, centre punch, dividers, odd-leg jenny, surface plate and height gauge; punch the centre before drilling.

Allowance is extra material added for sawing, filing, machining or bending; tolerance is the permitted variation in a finished dimension.

Go/no-go gauges check maximum and minimum limits, a feeler gauge measures small gaps, and a dial test indicator shows run-out.

Zero error: if a vernier reads 0.03 mm when closed, subtract 0.03 mm from positive readings and add it to negative readings.

Single-cut files suit finishing and sharpening, double-cut files remove stock quickly; bastard is coarse, second cut is medium and smooth is fine.

Fit a file handle, use two hands, file away from the vice and clean teeth with a file card; never use a file as a lever.

Hacksaw blade pitch: 18 TPI for general mild steel, 24–32 TPI for thin tube and sheet, and 14 TPI for thick sections; keep at least three teeth in contact.

Cold chisel cutting angle is about 60° for general steel, 70° for hard metal and 40° for soft metal; wear goggles and dress a mushroomed head.

Metric tap drill size = major diameter − pitch; M10 × 1.5 therefore uses an 8.5 mm drill.

Tapping sequence: centre drill, tap drill, countersink, then taper, second and plug taps with cutting fluid and a quarter-turn back to break chips.

Mount a bench vice at about elbow height, use soft jaws for finished surfaces, and never extend the handle with a pipe.

Screwdrivers must match the slot width and thickness; do not use a screwdriver as a chisel or pry bar.

Drill speed N = (1000 × Vc) / (π × D), where N is rpm, Vc is cutting speed in m/min and D is drill diameter in mm.

HSS cutting speeds: mild steel 25–30 m/min, cast iron 15–25 m/min, aluminium 60–90 m/min and brass 45–60 m/min.

Twist drill point angle is 118° for general steel and 135° for hard materials or sheet metal; lip clearance is 8–12° and both lips must be equal.

Clamp the work, remove the chuck key before starting, and do not wear gloves when operating a pedestal drill.

Cutting fluid: soluble oil for steel, paraffin for aluminium, and dry cutting for cast iron and brass.

A countersink cuts a conical seat for a screw head, a counterbore cuts a flat seat for a cap screw, and spot facing cleans a seating surface.

Reaming removes about 0.1–0.3 mm to finish a drilled hole to size; use the correct reamer and plenty of lubricant.

Bandsaws and abrasive cut-off saws cut bar and section; support long stock and avoid overheating the blade teeth.

Sheet thickness is given by gauge; a lower gauge number means thicker sheet, so 16 SWG is thicker than 20 SWG.

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

Bend deduction = 2 × outside setback − bend allowance; outside setback = (R + T) × tan(θ/2) for included bend angle θ.

Rivet pitch is about 3–4 times rivet diameter and edge distance about 1.5–2 times diameter; drill the hole about 0.1 mm larger than the rivet.

Straight snips cut general trimming, left-hand snips cut inside curves anticlockwise and right-hand snips cut outside curves clockwise.

Folding uses folding bars, stakes and a mallet; use a soft mallet on visible faces and allow for bend radius and springback.

Development methods: parallel line for prisms and cylinders, radial line for cones and pyramids, and triangulation for transition pieces.

Sheet metal joints include lap, grooved seam, Pittsburgh lock, riveted joint and folded edge; add joint allowance before cutting.

Annealing heats steel above the critical temperature and cools it very slowly, softening the metal, refining grain and relieving internal stress.

Normalising heats steel 30–50°C above the upper critical temperature and cools it in still air, refining grain and improving toughness.

Hardening heats steel to the austenitising temperature and quenches in water, oil or brine; water cools fastest and gives the highest hardness with more distortion.

Tempering reheats hardened steel below the lower critical temperature (about 150–650°C), holds and cools to reduce brittleness while retaining hardness.

Case hardening packs low-carbon steel in a carbon-rich compound, heats to about 900–950°C and quenches so the surface hardens while the core stays tough.

Mild steel forges at about 900–1250°C; stop forging below about 700°C to avoid cracking.

Quench severity: brine is faster than water, water faster than oil and oil faster than air; thick sections and alloy steels need slower quenching.

Forge tools include the anvil, tongs, cross-peen hammer, hot chisel, punch, fuller and swage block; keep the anvil dry to avoid a steam explosion.

Soft soldering uses filler melting below 450°C, brazing uses filler melting above 450°C, and welding melts the parent metal.

Tin-lead 60/40 solder melts at about 188°C; lead-free SAC solder melts at about 217–227°C.

Copper-zinc brazing filler flows at about 900°C; silver solder flows at about 600–750°C; use borax or proprietary flux and remove residue.

Capillary action fills a joint gap of about 0.05–0.2 mm; clean the surfaces, flux the joint, heat it and touch filler to the joint rather than the flame.

Zinc chloride flux suits soft soldering steel and galvanised sheet, rosin flux suits electrical work, and acid flux residue must be washed off.

For a bolted joint use the specified grade and torque, fit washers, and add a locking device such as a nyloc nut, spring washer or thread-locking compound.

Solid rivets suit structural work and blind rivets suit access from one side; drill size, grip length and mandrel diameter must match the rivet.

Heating galvanised or cadmium-plated parts releases toxic fume; remove the coating or use extraction and a respirator.

MMA electrode current is about 30–40 A per mm of electrode diameter, so a 3.2 mm electrode needs roughly 100–130 A.

E6013 is a rutile electrode for general work on AC or DC; E7018 is a low-hydrogen basic electrode that needs DCEP and dry storage at 250–300°C.

Arc length should be about one electrode diameter; a long arc causes spatter and porosity, while a short arc causes sticking and a rough bead.

MIG/MAG uses a continuous wire electrode and shielding gas; CO2 is cheap and gives deep penetration, while Ar/CO2 mixes give smoother transfer.

TIG uses a non-consumable tungsten electrode; use DCEN for steel and stainless steel and AC for aluminium to break the oxide layer.

Oxy-acetylene neutral flame is about 1:1 oxygen to acetylene; excess acetylene gives a carburising feather and excess oxygen gives a short oxidising flame.

Defects: porosity from gas or dirt, slag inclusion from poor cleaning, lack of penetration from low current or fast travel, and undercut from high current or long arc.

Distortion control: tack weld, use a balanced or backstep sequence, clamp or pre-set the joint, and allow cooling between passes.

First-angle projection places the view from the front on the plane behind the object, so the top view appears below the front view; third-angle places the view between observer and object.

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

Scale 1:1 is full size and 1:10 reduces ten times; state the scale and give dimensions in millimetres unless another unit is stated.

Dimension from a datum, avoid duplicate dimensions and do not dimension to hidden lines; show diameter with Ø and radius with R.

A section view uses hatching at 45° to show cut material; adjacent parts use different hatch angles or spacing.

ISO fit H7/h6 is a clearance fit, where H7 is the hole tolerance and h6 is the shaft tolerance; interference fits need force or heat.

Surface finish is specified as Ra in micrometres; a smaller Ra value means a smoother surface.

On a welding symbol the arrow points to the joint, the reference line carries the symbol, and the fillet triangle above or below the line shows arrow-side or other-side welding.