Machinery's Handbook, 31st Edition
Taps
969
TAPS A tap is a mechanical device applied to make a standard thread on a hole. A range of tap pitch diameter (PD) limits, from which the user may select to suit local conditions, is avail able. Taps included in the ANSI/ASME B94.9 standard are categorized according to type, style, size and chamfer, and blank design. General dimensions and tap markings are given in the standard ANSI/ASME B94.9 Taps: Ground Thread With Cut Thread Appendix (Inch and Metric Sizes) for straight-fluted taps, spiral-pointed taps, spiral-pointed-only taps, spiral-fluted taps, fast spiral-fluted taps, thread-forming taps, pulley taps, nut taps, and pipe taps. The standard also gives the thread limits for taps with cut threads and ground threads. The tap thread limits and tolerances are given in Table 2 to Table 4, tap dimensions for cut thread and ground thread are given in Table 5a through Table 10. Pulley tap dimensions and tolerances are given in Table 12, straight and taper pipe thread tap dimensions and tolerances are given on Table 13a and Table 13b, and thread limits for cut thread and ground thread taps are given in Table 15 through Table 26a. Thread Form, Styles, and Types Thread Form.— The basic angle of thread between the flanks of thread measured in an axial plane is 60 degrees. The line bisecting this 60° angle is perpendicular to the axis of the screw thread. The symmetrical height of the thread form, h , is found as follows: (1) The basic pitch diameter (PD) is obtained by subtracting the symmetrical single thread height, h , from the basic major diameter as follows: (2) D bsc = basic major diameter P = pitch of thread Types and Styles of Taps.— Tap type is based on general dimensions such as standard straight thread, taper and straight pipe, pulley, etc., or is based on purpose, such as thread forming and screw thread inserts (STI). Tap style is based on flute construction for cutting taps, such as straight, spiral, or spiral point, and on lobe style and construction for forming taps, such as straight or spiral. Straight-Flute Taps: These taps have straight flutes of a number specified as either standard or optional, and are for general purpose applications. This standard applies to machine screw, fractional, metric, and STI sizes in high-speed steel ground thread, and to machine screw and fractional sizes in high speed and carbon steel cut thread, with taper, plug, semibottom, and bottom chamfer. h = symmetrical height of thread n = number of threads per inch h 0.64951905 P = n 0.64951905 = Basic Pitch Diameter D h bsc = −
BLANK Design 3
BLANK Design 1
BLANK Design 2
Spiral-Pointed Taps: These taps have straight flutes, and the cutting face of the first few threads is ground at an angle to force the chips ahead and prevent clogging in the flutes. This standard applies to machine screw, fractional, metric, and STI sizes in high-speed
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