Business / Machine Shop Glossary

Pitch Diameter: The diameter of a thread at an imaginary point where the width of the groove and the with of the thread are equal.

Pitch Line: An imaginary line which passes through threads at such points that the length of the part of the line between adjacent threads is equal to the length of the line within a thread.

Plain Cutter: A milling cutter with cutting teeth on the periphery (circumference) only.

Play: The looseness of fit (slack) between two pieces.

Plug Weld: A weld made in a circular hole in one member of a joint fusing that member to another member.

Powder Coating: A durable, weather-proof, polymer coating for metals applied in a spray and then cured in an oven.

Prick Punch: A solid punch with a sharp point, used to mark centers or other locations on metal.

Proportional Limit: The greatest stress a material can withstand without deviation from the straight-line proportionality between stress and strain.

Protective Atmosphere: A gas or vacuum envelope surrounding the workpieces, used to prevent or reduce the formation of oxides and other detrimental surface substances and to facilitate their removal.

Pyrometer: A device for measuring the high temperatures in a heat-treating furnace.

Quenching: The sudden cooling of heated metal by immersion in water, oil, or other liquid. The purpose of quenching is to produce desired strength properties in hardenable steel.

Quick Return: A mechanism on some machine tools that provides rapid movement of the ram or table on the return or anointing stroke of the machine.

Rack: An array of gears spaced on a straight bar.

Radial: In a direction directly outward from the center of a circle or sphere or from the axis of a cylinder. The spokes of a wheel, for example, are radial.

Radius: The distance from the center of a circle to its circumference (outside).

Radius Gage: Any one of a number of small, flat, standard-shaped metal leafs or blades used for checking the accuracy of regular concave and convex surfaces.

Rake: That surface of a cutting tool against which the chips bear while being severed. If this surface is less than 90º from the surface being cut, the rake is positive, if more, the rake is negative.

Ram: That part of a shaper which moves back and forth and carries the tool head assembly.

Rapid Traverse: A lever-controlled, power-operated feature of some machines that permits the rapid movement of the worktable from one position to another.

Recess: An internal groove. See undercut.

Relief: A term for clearance or clearance angle.

Residual Stress: Stress present in a joint member or material that is free of external forces or thermal gradients.

Rockwell Hardness Test: The most common hardness testing method. This procedure uses a minor load to prevent surface irregularities from affecting results. There are nine different Rockwell hardness tests correspon . . . View Full Definition

Rough Machining: Removing excess stock (material) with a machine tool thus shaping it in preparation for finish machining.

Roughing: The fast removal of stock to reduce a workpiece to approximate dimensions, leaving only enough material to finish the part to specifications.

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