Pancyprian Machine Elements T.S. (Practical) key terms

A drawing view in which the object is imagined cut by a plane and the cut surface is hatched, so hidden internal features such as bores, keyways and oil passages become visible and dimensionable.

Thin parallel lines at about 45 degrees that fill the cut areas of a sectional view. Adjacent parts in an assembly are hatched at different angles or spacings so their boundaries remain distinguishable.

A dashed line showing an edge that is not directly visible from the viewing direction. It is normally omitted where a section already reveals the feature, to keep the drawing readable.

A drawing showing several parts in their working positions, with item numbers, a parts list and overall dimensions. It explains how components fit together rather than how each one is manufactured.

An assembly drawing in which parts are drawn separated along their assembly axis, with thin lines showing the order of insertion. It is used for dismantling sequences and for parts identification in maintenance manuals.

A symbolic system for specifying form, orientation, location and runout tolerances using rectangular frames with a characteristic symbol, tolerance value and datum references, instead of relying on note text alone.

A theoretically exact reference feature, such as a machined face or a shaft axis, from which location and orientation tolerances are measured. Datum features are usually established on the machine before other features are cut.

A permitted deviation of form or position, for example flatness, cylindricity, perpendicularity or concentricity, stated in millimetres or as a diameter zone. It controls shape and relationship, not the size of the feature.

A fit in which the largest shaft is still smaller than the smallest hole, so the parts always assemble with play. It is chosen where rotation or sliding must be free, as in plain bearing journals.

A fit in which the smallest hole is smaller than the largest shaft, so assembly requires force, heating or cooling. It transmits torque without keys and is used for bearing inner rings on rotating shafts.

A fit that may give either a small clearance or a small interference depending on the actual sizes within the tolerance zones. It locates parts precisely while still allowing dismantling with light force.

A tolerance system in which the hole tolerance zone has a fixed position, usually H, and the required fit is obtained by choosing the shaft letter. It reduces the number of reamers and gauges needed in production.

The basic size is the nominal dimension from which limits are derived. The deviation is the signed distance of a tolerance limit from that basic size, for example the upper deviation of an h7 shaft.

An iron-carbon alloy with small amounts of manganese and silicon and no deliberate alloying additions. Properties depend mainly on carbon content, so it is cheap but limited in hardenability and corrosion resistance.

Steel to which elements such as chromium, nickel, molybdenum or vanadium are added to improve hardenability, toughness, wear resistance or high-temperature strength. It needs correct heat treatment to give its designed properties.

An iron-carbon alloy with carbon typically above two percent, usually containing free graphite. It has good damping and compressive strength but low tensile ductility, so it suits machine bases and housings rather than shafts.

Copper-based alloys, often with tin, lead or aluminium, used for bushes and worm wheels because they run against steel with low friction and embed small particles. They tolerate marginal lubrication better than steel on steel.

A light metal alloy, often with silicon, magnesium or copper, giving a high strength-to-weight ratio and good machinability. It needs anodising or coating for wear and corrosion resistance on sliding surfaces.

Heating steel above its transformation temperature, quenching to form martensite, then reheating to a lower temperature to trade some hardness for toughness. Tempering temperature is chosen from the required strength and impact resistance.

Adding carbon, and sometimes nitrogen, to the surface of low-carbon steel, then hardening so that a hard wear-resistant skin forms over a tough core. Used for gears, pins and shafts that must resist wear and shock.

Local surface hardening by eddy-current heating of a defined area with a shaped coil, followed by immediate quenching. It gives a hard wear layer on selected zones such as journals while the core stays tough.

The fluid or gas, such as water, polymer solution, oil or air, used to cool a part fast enough to harden it. Selection balances the required hardness against the risk of cracking and distortion.

The depth to which a steel can be hardened under a given quench, governed mainly by its alloy content and grain size. A high-hardenability steel hardens deeply even in oil, reducing distortion compared with water quenching.

An electrolytic process that grows a controlled oxide layer on aluminium for corrosion and wear resistance and for dyeing. The layer is hard but brittle, so it is avoided on parts that must flex.

A measuring tool with a main scale and a sliding vernier scale, giving readings to 0.02 or 0.05 mm. It measures outside, inside and depth dimensions, and must be checked against zero before use.

A precision instrument using a calibrated screw and thimble, usually reading to 0.01 mm with an estimate to 0.001 mm. It gives higher accuracy than a caliper but measures a limited range and needs a zero check.

A reading shown by an instrument when the measurement should be zero, caused by wear, dirt or misadjustment. It is recorded and added or subtracted from every reading, or the instrument is adjusted and recalibrated.

Comparing an instrument's readings with a traceable reference standard and recording the deviation. It establishes whether the tool is fit for the tolerance being measured and sets the interval for the next check.

A spring-loaded instrument with a plunger or lever and a dial, used for runout, concentricity and alignment checks. Its reading shows deviation from a reference, not an absolute dimension.

Machining on a lathe where the workpiece rotates and a single-point tool feeds along or across it, producing cylindrical surfaces, faces, grooves and threads. Speed, feed and depth of cut determine finish and tool life.

Machining with a rotating multi-tooth cutter while the workpiece is fed, producing flat faces, slots, keyways and profiles. Up-cut and down-cut directions affect chip formation, finish and clamping forces.

Drilling produces a hole with a twist drill, typically slightly oversize and rough. Reaming then removes a small amount of material with a multi-edge reamer to achieve accurate diameter and fine finish for fits.

Cutting speed is the surface speed between tool and workpiece, in metres per minute; feed is the advance per revolution or per tooth. Both are selected from the work material and tool material to control finish and life.

Dismantling tools that apply axial force to a bearing ring, never through the rolling elements. A puller draws the ring from the shaft; a press pushes it out of a housing with controlled, square force.

Equipment that heats a bearing or ring by induced current so it expands for interference assembly, avoiding hammer blows. The part is heated to a controlled temperature and slid square onto its seat.

Controlling clamped joint behaviour with the correct torque, tightening sequence and locking method, such as thread-locking fluid, tab washers or prevailing-torque nuts. Preload keeps joints from loosening under vibration.

A wrench that signals when a set tightening torque is reached, giving repeatable preload in bolts. It must be stored at its lowest setting and calibrated, because an out-of-tolerance wrench can strip threads or leave joints loose.

A bearing in which a shaft slides on a bush or on a film of lubricant, with no rolling elements. It is quiet, compact and tolerant of shock, but needs a continuous oil film to avoid metal-to-metal contact.

The standard number code identifying a bearing's type, dimension series and bore. For common metric bearings, the last two digits times five give the bore in millimetres, so 6205 has a 25 mm bore.

The small internal gap between rolling elements and raceways, measured as radial or axial clearance. Correct clearance allows for interference mounting and thermal expansion; too little causes overheating and seizure.

A low-melting tin- or lead-based bearing alloy with good embeddability and conformability, cast or lined into shells. It tolerates slight misalignment but has low strength at high temperature.

A rotary shaft seal with a flexible lip pressed against the shaft by a garter spring, retaining oil and excluding dirt. The lip must run on a smooth, hard surface with the correct interference and lubrication.

A moulded elastomer ring seated in a groove and compressed to seal static or slow-moving joints. Correct groove dimensions, squeeze and material compatibility with the fluid are essential to avoid swelling or leakage.

A measure of a fluid's resistance to flow, falling as temperature rises. It determines film thickness in bearings and gears, so the grade is chosen for the operating temperature and speed of the machine.

The stiffness of a grease, graded by penetration number such as NLGI class 2. Softer grease flows more readily into a bearing; harder grease stays in place in vertical or high-temperature applications.

Examining a failed bearing's marks, colour and wear pattern to identify the cause, such as misalignment, inadequate lubrication, contamination or wrong mounting. The pattern points to the correction needed before replacement.

A steel key seated in matching slots in shaft and hub to transmit torque positively while allowing dismantling. The key is the weaker, replaceable element, so it fails before the shaft is damaged.

Setting two coupled shafts so their axes are collinear within tolerance, using straightedges, dial indicators or laser systems. Misalignment causes vibration, coupling wear and premature bearing failure.

Correcting angular and parallel offset between driver and driven shafts before tightening the coupling. Soft-foot checks and shimming under the motor feet are done first, then alignment is rechecked after running.

Setting belt preload and matching pulley grooves so the belt runs straight and does not slip or overload bearings. Too tight a belt damages bearings; too loose a belt slips and wears rapidly.

The total movement of a rotating surface measured by a dial indicator as the part turns, combining eccentricity and out-of-squareness. Excessive runout causes vibration and seal leakage.

Isolating all energy sources of a machine, locking the isolator and attaching a personal tag before maintenance. It prevents unexpected start-up or release of stored energy such as pressure or springs.

Physical barriers, interlocks or light curtains that keep hands away from rotating parts, belts, gears and cutting tools. Guards must be in place before start-up and must not be bypassed for convenience.

Items worn by the worker, such as safety glasses, hearing protection, gloves and safety shoes, as the last line of defence. Gloves are removed near rotating shafts because they can be caught.

Separating metal swarf, used oil, coolant and general waste into correct containers for authorised disposal or recycling. Mixing streams makes recycling impossible and breaches environmental obligations.

A documented set of checks, measuring methods, sample sizes and acceptance criteria applied at defined stages of work. It records results so that nonconforming parts are identified before assembly or delivery.