Machining Fundamentals 616
M-codes: Miscellaneous codes in the
ANSI EIA 274D code format that control
machine functions in CNC programming.
(Ch. 23)
medium-carbon steels: Steel that contains
0.30% to 0.60% (30 to 60 points) carbon.
The carbon content is sufficient to allow
partial hardening with proper heat
treatment. (Ch. 28)
megahertz (MHz): A unit of measure equal to
a million cycles per second. Used to measure
ultrasound frequencies. (Ch. 27)
metal finish: The degree of smoothness or
roughness remaining on the surface of a part
after it has been machined. (Ch. 30)
metal spraying: A process in which a metal
wire or powder is heated to its melting
point and sprayed by air pressure to
produce the desired coating on the work
surface. (Ch. 30)
metrology: The science that deals with systems
of measurement. (Ch. 5)
microinch: One millionth of an inch. (Ch. 30)
micrometer: One-millionth of a meter
(0.000001 m). Also called micron. (Ch. 5, 30)
micrometer caliper: A precision tool capable
of measuring to 0.001″ (0.01 mm). When
fi tted with a vernier scale, it will read to
0.0001″ (0.002 mm). Also known as a “mike.”
(Ch. 5)
micron: One-millionth of a meter (0.000001 m).
Also called micrometer. (Ch. 5)
mild steel: Steel that contains less than 0.3%,
or 30 points, or carbon. Mild steel does not
contain enough carbon to be hardened.
However, case hardening is possible if the
surface is exposed to an external source of
carbon during the process. Also called low-
carbon steel. (Ch. 28)
milling machine: A machine that removes
material from work by means of a rotary
cutter. (Ch. 1)
mineral oil: Cutting fl uid best suited for light-
duty (low speed, light feed) operations where
high levels of cooling and lubrication are not
required. (Ch. 10)
minor diameter: The smallest diameter of
a screw thread, measured across roots and
perpendicular to axis. Also known as “root
diameter.” (Ch. 16)
mist coolant: Cutting fl uid applied on a band
machine by fl ooding in mist form. It is used
for high-speed sawing of free machining
nonferrous metals. It is also used when
tough, hard-to-machine materials are cut.
(Ch. 21)
modal command: A G-code command that,
once activated, remains activated until
the machine encounters another modal
command in the CNC program. (Ch. 23)
N
newton meter (N·m): The SI Metric
measurement unit for torque. (Ch. 7)
nondestructive testing: A quality control
process in which the usefulness of the
product is not impaired. Also known
as “nondestructive examination” and
“nondestructive inspection.” (Ch. 27)
nonferrous: Containing no iron. (Ch. 28)
normalizing: A process that refi nes the
grain structure of some metals and thereby
improves their machinability. It is closely
related to the annealing process. (Ch. 29)
numerical control (NC): A system (composed
of a control program, a control unit, and
a machine tool) that controls the actions
of the machine through coded command
instructions. (Ch. 1)