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ASME B1.5 Document Information:
Title
Acme Screw Threads
ASME International
Publication Date:
Jan 1, 1997
Scope:
This Standard provides for two general applications of Acme threads:
namely, general purpose and
centralizing.
The limits and tolerances in this Standard relate to single-start Acme
threads and may be used, if
considered suitable, for multiple-start Acme threads. The latter
threads are used to provide
relatively fast traversing motion when necessary.
The three classes (2G, 3G, and 4G) of general purpose threads have
clearances on all diameters for
free movement. This thread relies on the thread flanks to maintain
concentric operation.
The three classes of centralizing threads have a limited clearance at
the major diameters of the
external and internal threads so that a bearing at the major diameter
maintains approximate
alignment of the thread axis and prevents wedging on the flanks of the
threads.
For any combination of the three classes of threads covered in this
Standard, some end play or
backlash will result. This is unavoidable for interchangeable
products. When backlash or end play
is objectionable, some mechanical means should be provided to
eliminate the condition. In any case,
sufficient end play must be left to provide a close running fit.
In addition to limiting dimensions for the standard series of
diameters and pitches of Acme
single-start threads, tables of tolerances, in terms of pitch and
diameter, provide for a wide
choice of diameters for a given standard pitch. By using the formulas
for diameter and pitch
increments, the pitch diameter tolerances for special diameters and
pitches can be determined for
each class. Formulas and data are also provided for allowances on
external threads and major and
minor diameter allowances and tolerances.
The Appendices provide text and dimensions on the following:
(a) Alternate Centralizing Acme Threads. Appendix A uses the minor
diameter to ensure concentric
operation.
(b) Multiple-Start Acme Threads. Appendix B includes formulas for
limits of size. Multiple-start
threads may require additional allowances and/or tolerances for
satisfactory operation.
(c) General Purpose Acme Threads, Class 5G. See Appendix C.
(d) Centralizing Acme Threads, Classes 5C and 6C. See Appendix D.
(e) Three-Wire Method of Measurement of Pitch Diameter of 29 deg
External Acme Screw Threads. See
Appendix E.
(f) Ball Methods for Internal Pitch Diameter Measurement of 29 deg
Acme Screw Threads. See Appendix
F.
(g) Go Gage Compensation, Calculation of Flank Angle, Limit Gaging of
Setting Rings, and Gaging
Problem Areas. See Appendix G.
(h) Tolerances for Acme Screw Thread Gages Over 5 in. See Appendix H.
(i) Determining Limits of Size for Special Diameter/Pitch
Combinations. See Appendix I .
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