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ANSI/ASME B1.5 ACME Screw Threads

ANSI/ASME B1.5 ACME Screw Threads

This Standard provides for two general applications of ACME screw threads: namely, General Purpose ACME and Centralizing ACME. If you are looking for data related to Stub ACME screw threads you need to refer to ANSI/ASME B1.8.

The limits and tolerances in this Standard relate to single-start ACME screw threads and may be used, if considered suitable, for multiple-start ACME screw threads. The latter screw threads are used to provide relatively fast traversing motion when necessary.

The three classes-of-fit (2G, 3G, and 4G) of general purpose screw threads have clearances on all diameters for free movement. This screw thread relies on the screw thread flanks to maintain concentric operation.

The three classes of centralizing ACME screw threads have a limited clearance at the major diameters of the external and internal screw threads so that a bearing at the major diameter maintains approximate alignment of the screw thread axis and prevents wedging on the flanks of the screw threads.

For any combination of the three classes of screw 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 screrw 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 screw threads and major and minor diameter allowances and tolerances.

The Appendices provide text and dimensions on the following:

(a) Alternate Centralizing ACME Screw Threads. Appendix A uses the minor diameter to ensure concentric operation.

(b) Multiple-Start ACME Screw Threads. Appendix B includes formulas for limits of size. Multiple-start screw threads may require additional allowances and/or tolerances for satisfactory operation.

(c) General Purpose ACME Screw Threads, Class 5G. See Appendix C.

(d) Centralizing ACME Screw Threads, Classes 5C and 6C. See Appendix D.

(e) Three-Wire Method of Measurement of Pitch Diameter of 29° External ACME Screw Threads. See Appendix E.

(f) Ball Methods for Internal Pitch Diameter Measurement of 29° 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 .

This data is accurate to the best of my knowledge as of 10/15/09.
Last Revised on: 5/13/2020
If you notice an error, or to submit other editorial comments, contact Wayne at:office@gagecrib.com

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