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Tap Terminology
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Axis-The longitudinal centerline of the tap.
Basic-Plane
is vertical with axis of taper thread ,owns base diameter.
Chamfer-The
tapering of threads at the front end of the tap to provide
a start ,measured in relation to the axis of the tap.
Chamfer
angle-The angle formed between the chamfer and the axis
of the tap ,measured in an axis plane at the cutting edge.
Chamfer
lenghth-The lenghth of chamfer measured parallel to the
axis at the cutting edge.
Core-The
diameter of the body of the tap between the flutes.
Cutting
edge -That portion of the land that does the cutting.
Chip
flutes-The longitudinal grooves in the threads portion
of a tap whose geometry form the cutting edge .The flutes
introduce lubricant to the cutting teeth and accommodates
chips.
Heel
-The back edge of the land.
Helix-the
angle at which the thread is ground to give the tap its
advance .Also used to describe the angle of the flutes
in spiral flut tap.
Hook
-The circular ground portion of the cutting face.
Helix
angle -On pitch diameter taper and cylinder ,the angle
which between the helix tangent and vertical to thread
axis.
Land
-The threaded section of the tap between the flutes.
Lead
- The advance of the tap in one complete revolution.
Pilot
- A cylinder or threaded section of the tap ,usually in
front of the thread section the tap ,ground to enter a
predrilled or threaded hole to maintain alignment.
Pitch
- The width of one thread usually expressed in terms of
the number of threads to the inch except in metric taps
which the pitch given is the width of one thread in millimeters.
Pitch
Diameter -The diameter of an imaginary cylinder midway
between the theorietical major and minor diameter of thread.It
is usually measured by means three wires at the first
full threads behind the chamfer.
Rake-
A straight angle in the cutting face of the flute,either
positive or negitive.
Relief
-Back taper is a form of relief.Pitch diameter relief
can be Eccentric:relieved from the cutting face to the
heel of the thread.Coneccentric: a portion of the land
is concentric before the relief starts.This can be 1/3
concentric and 2/3 eccentric.OD relief is silar to PD
relief if applied ;but since an extra operation is needed.
Root
-That portion of the tap where two threads are jointed
.
Shank
- That portion of the tap by which it is hold.
Square
-That portion of the tap behind the shank usually used
to drive the tap.
Spiral
point -An offset section of the flute at the cutting edge
used to impart a shearing or throwing action to effect
an ejection of chips in through holes .Somtimes called
chip drivers.
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