TAP NOMENCLATURE
Bottoming Tap
A
tap having a chamfer length of 1-2 threads.
Chamfer
The
tapering of the threads at the front end of each land of a chaser, tap or die
by cutting away and relieving the crest of the first few teeth to distribute
the cutting action over several teeth.
Chamfer Angle
The
angle formed between the chamfer and the axis of the tap or die by cutting away
the relieving the crest of the first few teeth to distribute the cutting action
over several teeth
Crest
The
surface of the thread which joins the flanks of the thread and it’s farthest
from the cylinder or cone from whi8ch the thread projects
Flank
The
part of a helical thread surface which connects the crest and the root and
which is theoretically a straight line in an axial plane section.
Flute
The
longitudinal channel formed in a tap to create cutting edges on the thread
profile and to provide chip spaces and cutting fluid passage.
Hand of Threads
A
thread when viewed axially, winds in a clockwise and receding direction for
LEFT-HAND THREADS and counter clockwise and receding direction for RIGHT-HAND
THREADS
Hook, Chordal
A
concave face having an angle of inclination specified between a chord passing
through the root and crest of a thread form at the cutting face, and a radical
line through the crest at the cutting edge.
Hook, Tangential
A
concave face having an angle of inclination specified between a line tangent to
the hook surface at the cutting edge and a radial line to the same point.
Hook Angle
The
angle of inclination of a concave face usually specifies either as CHORDAL HOOK
or TANFENTIAL HOOK
Interrupted Thread Tap
A
tap having an odd number of lands with alternative teeth in the thread helix
removed. In some cases alternative teeth are removed only for a portion of the
thread length.
One of the threaded
sections between the flutes of a tap
lead of Thread
The distance a screw thread advances axially in one complete turn. On a single start tap the lead and pitch are identical. In a multiple start tap the lead is the multiple of the pitch
Major Diameter
The diameter of the major cylinder or cone, at a given position on the axis that bounds the roots an external thread of the crests of an internal thread
Minor Diameter
The diameter of the minor cylinder or cone, at a given position on the axis that bounds the roots an external thread of the crests of an internal thread
Pitch Diameter
The diameter of an imaginary cylinder or cone, at a given point on the axis, of such a diameter and location of its axis that its surface would pass through the thread in such a manner as to make the thread ridge and the thread groove equal and, therefore, is located equidistant between the sharp major and minor cylinders or cones of a given thread form. On a theoretically perfect thread, these widths are equal to one half of the basic pitch (measured parallel to the axis.) See illustration below.
Plug Tap
tap with 3 to 5 chamfered threads.
Spiral Point
The 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 great enough to direct the chips ahead of the tap. The tap may or may not have longitudinal lines.
Square
Four driving flats parallel
to the axis on a tap shank forming a square or square with round corners.Taper Tap
A tap having a chamfer length of 7 to 10 threads
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