Machining Fundamentals 622
tapping: Forming an internal screw thread
in a hole or other part by means of a tap.
Also, opening the pouring hole of a melting
furnace to remove molten metal. (Ch. 12)
technician: A specialist in the technical details
of an occupation operating between the
realms of the production and engineering
departments. (Ch. 2)
temper: The hardness and strength of a rolled
metal. (Ch. 13)
tempering: A heat treatment process that
reduces a metal’s brittleness or hardness.
In this process, metal is heated to a
temperature below its critical temperature
and then quenched. (Ch. 29)
thread cutting stop: A device used to stop the
thread-cutting operation on a lathe so the
tool can be removed from the work after each
cut and repositioned before the next cut is
started. (Ch. 16)
thread dial: A dial that meshes with the lead
screw of a lathe and indicates when to engage
the half-nuts, which permits the tool to
follow exactly in the original cut. (Ch. 16)
threaded fastener: A bolt or similar device that
uses the wedging action of the screw thread
to clamp parts together. To achieve maximum
strength, a threaded fastener should screw into
its mating part at least a distance equal to one
and one-half times the thread diameter. (Ch. 8)
three-tooth rule: In a properly selected power
hacksaw blade, at least three teeth must come
in contact with the work. (Ch. 11)
three-wire method: To accurately measure
thread size, three wires of a specifi c
diameter are fi tted into screw threads, and a
micrometer measurement is made over the
wires. A mathematical formula provides the
information necessary to calculate the correct
measurement. (Ch. 16)
tolerance: A permissible deviation from a
basic dimension. (Ch. 4)
tombstone: A common fi xture-holding device
used with machining centers and other CNC
machine tools. They are made from heavy
castings and are precisely machined. (Ch. 9)
toolmaker: A highly skilled machinist who
specializes in producing the tools and tooling
needed for machining operations. (Ch. 2)
tool post: Mounts the cutting tool on the
carriage of the lathe. (Ch. 14)
tool rest: A part found on bench, pedestal,
and belt grinding machines. Supports the
workpiece during grinding operations.
(Ch. 13)
tooth form: The shape of the tooth on a band
machine saw. There are three basic forms:
standard, skip, and hook. (Ch. 21)
tooth rest: A device that quickly and
accurately positions the teeth of a gear cutter.
torque: The amount of turning or twisting
force applied to a threaded fastener or part.
It is measured in force units of foot-pounds
(ft·lb) or the SI Metric equivalent, newton
meters (N·m). Torque is the product of the
force applied times the length of the lever
arm. (Ch. 7)
total runout: A type of runout that provides
a combined control of the circularity,
straightness, angularity, and cylindricity of a
surface rotated around a datum axis. (Ch. 4)
traverse grinding: A cylindrical grinding
operation where a fi xed amount of material
is removed from the rotating workpiece as it
moves past the revolving grinding wheel. Work
wider than the grinding wheel; can be ground
using this method. (Ch. 20)
turning: A machining process that operates on
the principle of work being rotated against
the edge of a cutting tool. (Ch. 1)
turning center: A CNC turning machine
equipped with an automatic tool changer.
(Ch. 22)