Rake:
Angular relationship of the straight cutting face of a tooth with
respect to a radial line through the crest of the tooth at the cutting edge.
Positive rake means that the crest of the cutting face is angularly ahead of
the balance of the cutting face of the tooth. Negative rake means that the
crest of the cutting face is angularly behind the balance of the cutting face
of the tooth. Zero rake means that the cutting face is directly on a radial
line.
Relief:
Removal
of metal behind the cutting edge to provide clearance between the part being
threaded and the threaded land.
Relief-Center:
Clearance
produced on a portion of the tap land by reducing the diameter of the entire
thread form between cutting edge and heel.
Relief-Chamfer:
Gradual
decrease in land height from cutting edge to heel on the chamfered portion of
the land on a tap to provide radial clearance for the cutting edge.
Relief-Con-eccentric Thread:
Radial relief in the thread form starting back of a concentric margin.
Relief-Double Eccentric Thread:
Combination of a slight radial relief in the
thread form starting at the cutting edge and continuing for a portion of the
land width, and a greater radial relief for the balance of the land.
Relief-Eccentric Thread:
Radial relief in the thread form starting at the cutting edge and continuing
to the heel.
Relief-Flatted
Land
:
Clearance produced on a portion of the tap land
by truncating the thread between cutting edge and heel.
Relief-Grooved
Land
:
Clearance produced on a tap land by forming a
longitudinal groove in the center of the land.
Relief-Radial:
Clearance
produced by removal of metal from behind the cutting edge. Taps should have the
chamfer relieved and should have back taper, but may or may not have relief in
the angle and on the major diameter of the threads. When the thread angle is relieved,
starting at the cutting edge and continuing to the heel, the tap is said to
have “eccentric” relief. If the thread angle is relieved back of a concentric
margin (usually one third of land width), the tap is said to have
“con-eccentric” relief.
Size-Actual:
Measured
size of an element on an individual part.
Size-Basic:
That
size from which the limits of size are derived by the application of allowances
and tolerances.
Size-Functional:
The
functional diameter of an external or internal thread is the pitch diameter of
the enveloping thread of perfect pitch, lead and flank angles, having full
depth of engagement but clear at crests and roots, and of a specified length of
engagement. It may be derived by adding to the pitch diameter in an external
thread, or subtracting from the pitch diameter in an internal thread, the
cumulative effects of deviations from specified profile, including variations
in lead and flank angle over a specified length of engagement. The effects of
taper, out-of-roundness, and surface defects may be positive or negative on either
external or internal threads.
Size-Nominal:
Designation
used for the purpose of general identification.
Spiral Flute:
See
Flutes.
Spiral Point:
Angular
fluting in the cutting face of the land at the chamfered end. It is formed at
an angle with respect to the tap axis of opposite hand to that of rotation. Its
length is usually greater than the chamfer length and its angle with respect to
the tap axis is usually made great enough to direct the chips ahead of the tap.
The tap may or may not have longitudinal flutes.
Thread Lead Angle:
On
a straight thread, the lead angle is the angle made by the helix of the thread
at the pitch line with a plane perpendicular to the axis. On a taper thread,
the lead angle at a given axial position is the angle made by the conical
spiral of the thread, with the plane perpendicular to the axis, at the pitch
line.
Copyright 2004,
Industrial Press, Inc., New York, NY