MSCE Metalwork key terms

Items worn or used by a worker to reduce exposure to hazards, such as safety glasses, face shields, gloves, hearing protection and safety footwear. In metalwork shops it supplements, but never replaces, guards and safe working procedures.

Physical barriers, interlocks or enclosures fitted to machines to prevent contact with moving parts, chips or sparks. Guards must be in place before starting work and must not be defeated or removed while the machine is running.

A safe isolation method in which the power source is switched off, isolated and locked or tagged so it cannot be re-energised while maintenance, tool changing or clearing of jams takes place. The person working holds the key or tag.

A structured assessment of substances used or produced in the workshop, such as cutting fluids, solvents, welding fume and dust, to identify health risks and specify controls. It records who is exposed, how, and what precautions are required.

The three conditions needed for combustion: fuel, oxygen and heat. Removing any one side extinguishes a fire, which explains why the correct extinguisher type and isolation of power or gas supply matter in a workshop.

A written authorisation for tasks producing flames, sparks or high heat, such as welding, grinding or brazing. It confirms fire precautions, clearance of combustibles, fire watch arrangements and the time and place of work.

A metal whose main constituent is iron, such as mild steel, cast iron and alloy steels. Ferrous metals are generally magnetic and, except for some stainless grades, susceptible to rusting when exposed to moisture.

A low-carbon steel containing roughly 0.1 to 0.3 percent carbon, widely used for general fabrication because it is cheap, ductile and easy to weld and machine. It has low hardenability and corrodes readily without protection.

A corrosion-resistant steel alloyed with chromium and nickel, usually with a face-centred cubic structure that is non-magnetic in the annealed condition. It work-hardens rapidly, welds well and is common in food and chemical equipment.

An iron-carbon alloy with carbon content above about two percent, usually 3 to 4 percent, giving good fluidity for casting and high compressive strength. It is brittle in tension and its graphite flakes damp vibration, making it useful for machine bases.

A light, corrosion-resistant metal, often alloyed with copper, magnesium, silicon or zinc to improve strength. It has about one third the density of steel, conducts heat well and forms a tough oxide layer, but is difficult to weld without special processes.

The relationship between the percentage of carbon in steel and its ability to harden when quenched. Steels with more carbon, roughly above 0.3 percent, respond strongly to heat treatment, while low-carbon steels cannot be hardened significantly.

Corrosion that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte, causing the more active metal to corrode preferentially. Insulating washers or suitable material pairing help prevent it.

A measuring instrument with fixed and sliding jaws and a vernier scale, used to read outside, inside and depth dimensions. The main scale and vernier scale are compared to read to typically 0.02 mm or 0.001 inch.

A precision measuring instrument using a calibrated screw and thimble to measure small dimensions, usually to 0.01 mm or 0.001 inch. The spindle closes onto the work and the reading is taken from the barrel and thimble scales.

A reference point, line or surface from which dimensions are measured or from which machining and marking out are set. Choosing a clear datum avoids accumulated error and keeps parts interchangeable during assembly.

Allowance is the intentional difference between two mating dimensions, such as a shaft and hole. Tolerance is the total permitted variation in a nominal size. Together they define fit and interchangeability on a drawing.

A system specifying the maximum and minimum permissible sizes of mating parts and the resulting clearance or interference. Hole-basis fits are common, where the hole size is fixed and the shaft varies to produce the required fit.

The number of teeth per inch on a hacksaw blade, chosen according to material thickness. Coarse pitches cut thick sections quickly, while fine pitches suit thin tube and sheet to avoid snagging or tooth breakage.

The pattern and coarseness of a file's teeth, such as single cut, double cut, bastard, second cut and smooth. Coarse grades remove metal quickly, while smooth grades produce a fine finish and are used for fitting and draw filing.

The diameter of the hole drilled before cutting an internal thread, chosen so that the tap cuts cleanly without binding. For metric threads it is approximately the nominal diameter minus the thread pitch.

Cutting internal threads with a tap and external threads with a die. Correct hole or bar size, lubrication and a square start are essential; taps are used in a set of taper, plug and bottoming types.

A clearance fit always leaves a gap between mating parts, allowing movement or easy assembly. An interference fit makes the shaft slightly larger than the hole, so parts must be pressed or shrunk together to transmit load without slipping.

Coating a metal surface with a thin blue dye so scribed lines are visible. The workpiece is then set on a surface plate and marked with a scriber, dividers, height gauge or centre punch before cutting or machining.

Joining metals by melting a filler alloy, usually a tin-lead or lead-free solder, at a temperature below about 450 degrees Celsius. The filler wets the joint without melting the parent metal, and flux removes oxide to allow bonding.

A joining process in which a filler metal with a melting point above about 450 degrees Celsius but below that of the parent metal is drawn into a closely fitted joint by capillary action. It produces stronger joints than soldering.

A chemical agent applied during soldering, brazing or welding that dissolves oxides and prevents new oxide forming, allowing the filler to wet the metal. Residues may be corrosive and often must be cleaned off afterwards.

A rivet is a headed fastener inserted through aligned holes and deformed to clamp parts together. Rivet allowance is the length of shank needed beyond the plates to form the closing head, typically about 1.5 times the diameter.

An arc welding process in which a flux-coated consumable electrode melts to form the weld while the decomposing coating shields the molten pool with gas and slag. It is versatile and portable but requires slag removal between passes.

Local exhaust ventilation or extraction equipment used to capture fumes and gases at the arc before they reach the welder's breathing zone. It is a key control because welding fume can cause serious respiratory and neurological harm.

Gas trapped in solidified weld metal, appearing as internal or surface holes that weaken the joint. Common causes include damp electrodes, dirty or oily surfaces, insufficient shielding gas and incorrect current settings.

Uneven heating and cooling during welding causes parts to shrink and pull, leaving locked-in stress and warping the assembly. Balanced welding sequences, tacking, jigs and stress relief reduce these effects.

A hem is a folded edge that stiffens and smooths a sheet edge for safety. A seam joins two folded edges, either by interlocking and flattening or by folding and soldering, producing a stiff joint without fasteners.

When sheet is bent, the inner surface compresses and the outer stretches, while a neutral axis keeps its length. Bend allowance is the developed length of that axis, used to calculate the flat pattern size before forming.

An electrolytic process that thickens the natural oxide layer on aluminium, improving corrosion resistance and allowing dyeing. The coating is hard and decorative but can crack if the part is subsequently bent sharply.

Hardening involves heating steel above its critical temperature and quenching to form hard martensite. Tempering reheats it to a lower temperature to relieve brittleness and achieve the required balance of hardness and toughness.

The increase in strength and hardness, and loss of ductility, that occurs when a metal is plastically deformed at room temperature, as in rolling, drawing or bending. Annealing restores ductility by allowing new grains to form.

Turning reduces a workpiece's diameter as it rotates against a moving tool, while facing produces a flat end surface. Both require correct spindle speed, feed, depth of cut and rigid workholding for accuracy and tool life.

Cutting speed is the rate at which the tool edge passes through the material, usually given in metres per minute. Feed is the distance the tool advances per revolution or per tooth. Both affect finish, tool wear and temperature.

A drawing method showing separate views of an object, such as front, plan and side, arranged according to first-angle or third-angle convention. Hidden detail is shown dashed and dimensions are added to allow manufacture.

A drawing view in which the object is imagined cut away to reveal internal features. The cut material is shown with evenly spaced hatching lines, and hidden lines are normally omitted for clarity.