Machining Fundamentals 618
plain protractor: An angle-measuring tool
used in layout work when angles do not need
to be laid out or checked to extreme accuracy.
The head is graduated from 0° to 180° in both
directions for easy reading. (Ch. 6)
plain turning: Turning in which the entire
length of the piece is machined to a specifi ed
diameter. (Ch. 14)
platens: Flat metal plates used to provide
support behind the belt of an abrasive belt
grinder. (Ch. 20)
plunge grinding: Grinding method in which
work is mounted between centers and
rotated while in contact with the grinding
wheel. The area being ground is no wider
than the wheel face. (Ch. 20)
polar coordinate system: A coordinate
system in which straight-line distance and
travel angle are used to specify locations or
movement. (Ch. 22)
position tolerance: A tolerance used to defi ne
a zone in which the center, axis, or center
plane of a feature of size is permitted to vary
from true position. (Ch. 4)
post-processing: The process of translating
a CAM program into a format the CNC
controller can understand. (Ch. 23)
powder metallurgy (P/M): A manufacturing
process used to make parts by compressing
and heating metal powders. Also called sintering.
(Ch. 33)
precision grinding: A fi nishing operation
in which a minute amount of material is
removed with each pass of the grinding
wheel to generate a smooth, accurate surface.
(Ch. 20)
process annealing: Removing internal
stresses that have developed in parts that
have been cold worked, machined, or
welded. Also called stress-relieving. (Ch. 29)
profile geometric tolerance: A tolerance that
specifi es a uniform boundary along the true
profi le within which the elements of the
surface must lie. (Ch. 4)
profile of a line tolerance: A two-dimensional
or cross-sectional geometric tolerance that
extends along the length of the feature. (Ch. 4)
profile of a surface tolerance: A geometric
tolerance that controls the entire surface of a
feature or object as a single entity. (Ch. 4)
profilometer: An electronic instrument for
measuring surface roughness. (Ch. 4)
program zero position: For purposes of CNC
programming, a reference point specifi ed on
the part or on the work-holding device as the
zero position. (Ch. 24)
protective clothing: Clothing that is worn in a
machine shop to protect the body. Safety glasses
and hearing protectors are two of the most
important articles because shop areas produce
both noise and fl ying chips. Other protective
clothing includes steel-toed shoes, lead aprons,
caps or hairnets, and respirators. (Ch. 3)
Q
quality control (QC): A process that identifi es
and prevents potential product defects in
the manufacturing process before they can
cause injuries or damage and substandard
products. (Ch. 27)
quench: To cool a metal rapidly by immersing
it in a fl uid or spraying a fl uid on its surface.
(Ch. 29)
R
radiographic inspection: A nondestructive
testing method that uses X rays and gamma
radiation to detect fl aws (crack, pores, etc.) in
an object. Also known as “X-ray inspection.”
(Ch. 27)