Glossary of Technical Terms 623
turret lathe: A lathe equipped with a rotating
tower, or turret, that holds multiple tools and
can be revolved to present the appropriate tool
for a particular operation. Turret lathes can
also be controlled by a CNC program. (Ch. 15)
twist drill: A common drill made by forging or
milling rough fl utes and then twisting them
to a spiral shape. After twisting, the drills
are milled and ground to approximate size.
Finally, they are heat-treated and ground to
exact size. (Ch. 12)
U
ultrasonic-assist machining: A machining
process in which ultrasound waves are used to
enhance the function of a conventional machine
tool. (Ch. 32)
ultrasonic testing: A nondestructive testing
method that uses high-frequency sound waves
to detect fl aws and cracks in materials. (Ch. 27)
unassigned code: A code that can be assigned
to different functions on different types of
machine controllers for specialty purposes.
(Ch. 23)
Unified System: A thread form system adopted
by the powers that make up NATO after
World War II. (Ch. 7)
universal bevel protractor: An angle-
measuring tool used in layout work. This
tool consists of a dial, a base or stock, and
a sliding blade. It is graduated into 360°.
(Ch. 5)
universal tool and cutter grinder: A grinding
machine designed to support cutters
(primarily milling cutters) while they are
sharpened to specifi ed tolerances. Special
attachments permit straight, spiral, and
helical cutters to be sharpened accurately.
Other attachments enable the machine to be
adapted to all types of internal and external
cylindrical grinding. (Ch. 20)
US Conventional system: The “English”
system of weights and measures used in
the United States. Compare with SI Metric
system. Also known as “US Customary
system.” (Ch. 4)
V
V-block: A square or rectangular steel block
with a 90° V-groove through the center,
provided with a clamp for holding round
stock for drilling, milling, and laying out
operations. (Ch. 6)
ventilation: Circulation of air that brings fresh
air and lowers the concentration of toxic
fumes within the working area. (Ch. 3)
vernier caliper: A precision measuring
instrument, used for both inside and
outside measurements, that is accurate to
1/1000″ (0.001″) and 1/50 mm (0.02 mm).
(Ch. 5)
vernier protractor: An angle-measuring tool
used in layout work when angles must be
extremely accurate. With this tool, angles of
1/12 of a degree (5 minutes of arc) can be
precisely measured. (Ch. 6)
vertical machining center (VMC): A
machining center with a vertically oriented
spindle. (Ch. 22)
vertical milling machine: A type of milling
machine in which the cutter is normally
perpendicular (at a right angle) to the
worktable. On many vertical milling
machines, the spindle can be tilted to
perform angular cutting operations.
(Ch. 18)
vitreous enamel: A glass coating that can be
fused to most metals, including steel sheet
and cast iron surfaces. It forms an extremely
hard coating that is smooth and easy to
clean. (Ch. 30)