Red Seal Machinist key terms

A documented safety procedure that isolates a machine from every energy source, applies a personal lock and tag, and verifies zero energy before anyone reaches into the work zone. Only the person who applied a lock removes it.

Wearable barriers such as safety glasses, face shields, hearing protection, safety footwear, and barrier creams that reduce exposure to chips, coolant, noise, and sharp edges. PPE is the last line of defense after engineering controls.

Physical barriers, interlocks, and shields that prevent contact with rotating spindles, belts, gears, and cutting tools. Guards must be in place before start-up and must not be bypassed for convenience.

A standardized document supplied with a hazardous product that lists its hazards, required PPE, first-aid measures, storage, and spill response. Workers must know where sheets are kept and how to read them.

Ratios of the sides of a right triangle used to solve shop problems such as taper angles, bolt-hole circles, and sine-bar setups. Sine equals opposite over hypotenuse, cosine equals adjacent over hypotenuse, tangent equals opposite over adjacent.

The rule that the square of the hypotenuse equals the sum of the squares of the other two sides in a right triangle. Machinists use it to find unknown lengths in layouts, fixtures, and coordinate calculations.

The circle on which a set of equally spaced holes is located. Hole positions are computed from the circle diameter and the angular spacing, often using sine and cosine of each angle.

The speed at which the workpiece surface passes the cutting edge, expressed in surface feet per minute. It depends on tool material and work material, and converts to spindle rpm through the diameter.

The rate at which the tool advances into the work, given as inches per revolution for turning or inches per minute for milling. Feed controls chip thickness, finish, and tool load.

The thickness of material removed by each cutting edge per revolution, usually expressed in thousandths of an inch per tooth. It is calculated from feed rate, spindle speed, and the number of teeth.

A measuring tool with a fixed main scale and a sliding vernier scale that reads to thousandths of an inch or hundredths of a millimetre. It measures outside, inside, depth, and step dimensions.

A precision instrument using a calibrated screw and thimble to measure small dimensions, commonly reading to 0.0001 inch or 0.001 millimetre. Correct use requires a light, consistent measuring force and a zero check.

A gauge with a spring-loaded plunger that displays small linear displacements on a graduated dial. It is used for runout, alignment, flatness, and centering work on lathes and fixtures.

The full sweep of a dial indicator needle as a part or spindle is rotated one full turn. TIR equals twice the eccentricity and is the usual acceptance value for runout checks.

Precision steel or ceramic blocks lapped to very flat, parallel faces and calibrated thicknesses. Wrung together in combinations, they establish master sizes for calibrating instruments and checking fixtures.

A precision bar with two cylinders a known distance apart, used with gauge blocks to set or measure angles. The angle is found from the sine of the height difference divided by the cylinder spacing.

The number of teeth per inch on a saw blade. Coarse pitches clear chips in soft, thick sections, while fine pitches suit thin walls and hard material where teeth could snag or break.

The alternating side-to-side bend of saw teeth that makes the kerf wider than the blade body. Set provides clearance, reduces friction, and allows the blade to clear chips from the cut.

The width of material removed by a saw cut, determined mainly by tooth set and blade thickness. Kerf must be allowed for when cutting parts to a layout line.

A short, stiff drill with a pilot tip and a countersink body that creates a starting hole and chamfer for lathe work or for guiding a larger drill. It reduces drill wander on flat or curved surfaces.

The included angle formed by the cutting lips of a twist drill, commonly 118 degrees for general steel and 135 degrees for harder alloys. Point geometry affects centering, thrust, and hole quality.

The movable assembly at the far end of a lathe bed that supports a centre, holds drills in a chuck, or mounts a reamer. It can be offset to turn long tapers between centres.

Producing a conical surface by swivelling the compound rest, offsetting the tailstock, or using a taper attachment. The method chosen depends on taper angle, length, and whether the work is held between centres.

The upper lathe slide that rotates to a set angle and feeds by hand. It is used for short tapers, chamfers, and fine control of depth on shoulders and faces.

A self-centring lathe chuck whose jaws move together by scroll action. It grips round or hex stock quickly but offers limited accuracy and cannot hold irregular shapes without soft jaws.

A lathe chuck in which each jaw is adjusted separately with its own screw. It can hold odd shapes and be dialled in to very close concentricity, but setup takes longer than a scroll chuck.

A milling method where the cutter rotation matches the feed direction at the point of contact. It produces better finish and longer tool life on rigid machines with backlash-free table drives.

A milling method where cutter rotation opposes the feed direction, so each tooth starts thin and thickens. It suits older machines with backlash and is safer for roughing setups.

A rotating multi-tooth cutter that cuts on its periphery and its end, used for slots, pockets, profiles, and facing. Flute count and helix angle are selected for the work material.

An indexing attachment for a milling machine that rotates the work by precise fractions of a turn. It is used for gears, splines, and evenly spaced features using plain or differential indexing.

Rotating a workpiece by an exact angular amount between machining operations. Common methods include direct indexing plates, a dividing head with hole circles, and rotary tables.

The strength of the bond holding abrasive grains in a wheel, rated from soft to hard. Soft wheels release dull grains readily for hard work materials, while hard wheels last longer on soft materials.

A number describing abrasive grain size, with low numbers coarse and high numbers fine. Coarse grits remove stock quickly; fine grits produce smoother finishes and sharper edges.

Sharpening and trueing a grinding wheel face by removing dulled grains and loaded metal with a diamond or star tool. Regular dressing restores cutting action, form, and surface finish.

Two coordinate modes in CNC programming. Absolute coordinates are measured from a fixed origin, while incremental coordinates are measured from the current tool position.

A stored CNC value that tells the control where the part datum sits relative to machine home. Common offsets include G54 through G59, each holding X, Y, and Z shift values.

A CNC feature that shifts the tool path by the cutter radius so the programmed path follows the part profile. It allows one program to run with different cutter sizes.

A symbolic control placed in a feature control frame that limits form, orientation, location, or profile variation. Each control defines a tolerance zone and may reference datums.

A set of mutually perpendicular planes established by three datum features that locates and orients a part for inspection and tolerancing. Datum order in the frame defines the sequence of restraint.

The condition where a feature contains the most material, such as the largest shaft or smallest hole within limits. A tolerance applied at MMC gains bonus tolerance as the feature departs from that size.

The variation in a surface's position as a part is rotated about a datum axis. It is checked with a dial indicator and reported as total indicator reading over one revolution.

The distance between corresponding points on adjacent threads, gear teeth, or repeated features. Thread pitch and gear pitch set the relationship between rotation and linear travel.

On a thread, the diameter where the thread thickness equals half the pitch; on a gear, the reference circle used to define tooth size. Both are critical inspection dimensions.

The rotating shaft of a machine tool that holds and drives the cutting tool or workpiece. Spindle speed, accuracy, and rigidity directly affect finish and dimensional control.