BTEB Machinist key terms

Gear worn to reduce injury risk, such as safety glasses, goggles, face shields, gloves, safety shoes, and hearing protection. In a machine shop it is chosen for the specific hazard of each task.

Physical barriers, interlocks, or covers fitted around rotating parts, belts, gears, and cutting zones to keep hands and clothing away. Guards must never be removed for convenience while a machine can run.

A procedure for isolating a machine from every energy source, applying a personal lock and tag, and proving the isolation before maintenance. It prevents unexpected start-up or release of stored energy during repair and cleaning.

Keeping floors, benches, and machines free of chips, oil, tools, and scrap. Good housekeeping prevents slips, cuts, and fires, and makes inspection and measurement more reliable.

The rate at which the cutting edge moves relative to the work surface, usually expressed in metres per minute. It depends mainly on workpiece material and cutter material, and controls tool life and finish.

The distance the cutter or tool advances per revolution or per stroke of the machine. Feed affects chip thickness, surface finish, and the load on the tool and machine.

The thickness of material removed in one pass of the tool, measured perpendicular to the machined surface. It is balanced against feed and speed to keep forces and temperature within safe limits.

The rotational speed of the machine spindle, usually given in revolutions per minute. It is calculated from the chosen cutting speed and the diameter of the work or cutter.

A groove or step ground on a tool face that curls and breaks the chip into short lengths. Short chips are safer to handle, clear the cutting zone, and reduce the risk of entanglement.

The angle between the tool face and a reference plane, controlling how the chip flows over the tool. Positive rake reduces cutting force; negative rake strengthens the edge for heavy interrupted cuts.

The angle ground below the cutting edge so the tool flank does not rub on the machined surface. Too little clearance causes rubbing and heat; too much weakens the cutting edge.

Progressive loss of cutting-edge material through abrasion, adhesion, diffusion, or chipping. It shows as flank wear, cratering, or a built-up edge, and is monitored to decide when to regrind or replace the tool.

A liquid or mist applied at the cutting zone to cool the tool and work, lubricate, and flush away chips. Correct selection improves finish and tool life; incorrect use can cause staining or health hazards.

A heavy clamping device fixed to a bench, with two jaws closed by a screw, used to hold work for filing, sawing, and chiselling. Soft jaw covers protect finished surfaces.

Removing metal by pushing a file across the work at a controlled angle and pressure. A steady two-handed stroke with a slight rocking motion produces a flat surface and avoids rounded edges.

The pattern and spacing of teeth on a file, described as single, double, or rasp, and as bastard, second cut, or smooth. Coarse cuts remove metal fast; fine cuts give a smooth finish.

Holding a file across the work and pulling or pushing it lengthwise to remove fine amounts of metal and produce a smooth, flat finish. It is often used before polishing or fitting.

A hand saw with a thin, hardened blade held under tension in a frame, used to cut bar stock and pipe. Correct blade pitch and steady stroke speed prevent blade breakage and crooked cuts.

The number of teeth per inch on a hacksaw blade. Coarse pitch suits soft, thick sections; fine pitch suits thin tube and hard material, where coarse teeth would snag or strip.

A hand operation using a hardened scraper to remove tiny high spots from a surface, checked against a reference or marking compound. It is used to fit sliding surfaces and true machine ways.

A measuring tool with a main scale and a sliding vernier scale that reads outside, inside, and depth dimensions. The vernier divides the smallest main-scale division to give a finer reading.

A precision instrument using a calibrated screw and thimble to measure small dimensions, commonly to 0.01 mm. It is read on the sleeve and thimble scales and checked with a standard before use.

The smallest value an instrument can read directly. For a vernier caliper it equals one main-scale division divided by the number of vernier divisions, and it sets the resolution of every reading.

A false reading shown by an instrument when it should read zero, caused by wear, damage, or dirt on the measuring faces. It must be found and added to or subtracted from every reading.

A flat, rigid reference surface, usually cast iron or granite, used for marking out, inspection, and supporting work during measurement. Its accuracy depends on cleanliness and careful handling.

A measuring and marking tool with a vertical vernier scale and a scriber, used on a surface plate to set and transfer heights. It marks parallel lines and checks part height accurately.

Reference surfaces, axes, or points from which dimensions are measured and from which a part is set up. Consistent datums keep machining, marking out, and inspection results in agreement.

The total permissible variation in a dimension, equal to the difference between upper and lower limits. It defines how much a part may deviate while still functioning and being interchangeable.

The system that pairs hole and shaft limit sizes to produce clearance, transition, or interference assemblies. Correct selection gives the required freedom of motion or grip without trial-and-error assembly.

Adjusting two mating parts by hand methods such as filing, scraping, or lapping until they assemble and work as required. It is judged by feel, contact pattern, and the specified fit.

The headstock and tailstock centre points that define the axis of rotation for work held between centres. Correct alignment and lubrication of centres prevent taper and wear.

A self-centring lathe work-holding device whose jaws move together by a scroll plate. It grips round and hexagonal work quickly but has limited accuracy and holding force compared with a four-jaw chuck.

An independent-jaw chuck in which each jaw is adjusted by its own screw. It can hold irregular shapes and be set to high accuracy with a dial indicator, but setting takes longer.

Machining the end of a workpiece to produce a flat surface square to the axis of rotation. It is usually the first lathe operation and provides a reference for later length measurement.

Reducing the diameter of rotating work with a single-point tool fed parallel to the axis. Roughing removes most material; finishing produces the final size, finish, and tolerance.

Enlarging and truing an existing hole with a single-point tool on a lathe or boring machine. It corrects hole position and diameter and can produce accurate internal tapers and shoulders.

Finishing a drilled hole with a multi-edge reamer to improve size accuracy and surface finish. It removes only a small amount of material and does not correct a badly placed hole.

Making a hole with a rotating fluted drill, usually on a drill press or lathe. Correct speed, feed, and coolant control hole size, finish, and drill life.

Cutting an internal thread with a tap after drilling the correct tapping-size hole. The tap must be started square and lubricated, and reversed regularly to break chips and avoid breakage.

The distance between corresponding points on adjacent thread crests, measured along the axis. It governs the lead of a single-start thread and the drill size needed before tapping.

A measuring instrument with a spring-loaded plunger that shows small displacements on a graduated dial. It is used for centring work, checking runout, and verifying alignment.

Scheduled cleaning, lubrication, adjustment, and inspection carried out before faults develop. It keeps machines accurate and safe, reduces breakdowns, and extends the life of bearings and slides.

Applying the correct oil or grease to bearings, slides, and gears to reduce friction and wear and to carry away heat. Wrong grade or contaminated lubricant causes overheating and premature failure.

A component that supports a rotating or sliding shaft while allowing controlled relative motion. Plain, rolling, and thrust types each need correct fitting, alignment, and lubrication to last.

Bringing machine parts, shafts, or centres into the correct relative position so they share a common axis or plane. Poor alignment causes vibration, heat, rapid wear, and inaccurate work.

A metal whose main constituent is iron, such as mild steel, cast iron, and alloy steel. Ferrous metals are generally magnetic and, except for some stainless grades, prone to rust.

A metal containing little or no iron, such as aluminium, copper, brass, and bronze. These are generally non-magnetic, resist corrosion well, and are often softer and easier to machine.

A metal made by combining two or more elements to obtain properties better than those of the pure metal. Steel, brass, and bronze are common examples used throughout machine work.

The percentage of carbon in steel, which strongly affects hardness, strength, and machinability. Low-carbon steel is soft and weldable; higher carbon raises hardness but reduces ease of cutting.

Controlled heating and cooling of metal to change its structure and properties, as in annealing, normalising, hardening, and tempering. It relieves stress, softens for machining, or increases wear resistance.

Measuring a material's resistance to indentation or scratching, using methods such as Brinell, Rockwell, or Vickers. Results guide tool selection, verify heat treatment, and predict machinability.