Machinery's Handbook, 31st Edition
982 Taps Shank: The portion of the tool body by which it is held and driven.
Shaving: The excessive removal of material from the product thread profile by the tool thread flanks caused by an axial advance per revolution less than or more than the actual lead in the tool. 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. Taper, Back: A gradual decrease in the diameter of the thread form on a tap from the chamfered end of the land towards the back, which creates a slight radial relief in the threads. Taper per Inch: The difference in diameter in one inch measured parallel to the axis. Taper Tap: A tap having a chamfer length of 7 to 10 pitches. Taper Thread Tap: A tap with tapered threads for producing a tapered internal thread. Thread, Angle of: The angle between the flanks of the thread measured in an axial plane. 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. Thread per Inch: The number of thread pitches in one inch of thread length. Tolerance: The total permissible variation of size or difference between limits of size. Total Indicator Variation (TIV): The difference between maximum and minimum indi cator readings during a checking cycle.
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