Centralizing ACME screw threads are defined by ANSI/ASME
B1.5.
The thread form for Centralizing Acme screw threads is the same as General
Purpose Acme Threads with the exception that the Centralizing Acme
Screw Threads have a limited clearance at the major diameter of both the
internal and external screw threads, and are used extensively for feed
screws. The restricted clearance enables a bearing at the major
diameter of the thread to preserve alignment of the thread axis
preventing wedging on the flanks and part sagging.
Five classes-of-fit are used with the Centralizing Acme threads: 2C, 3C,
4C, 5C, and 6C. For any combination of the five classes of threads
covered within the standard (ANSI B1.5) some end-play or backlash
will result. Although 5C and 6C are intended to allow for restricted
backlash they are not recommended for new designs.
A series of diameters and pitches is recommended in ANSI/ASME B1.5 which have been chosen to aid in industry standardization. By utilizing the recommended sizes, companies can limit their inventory of both
tools and gages. The tolerances specified in this standard are applicable
to lengths of engagement not exceeding twice the nominal major diameter
as well as to insure interchangeability and maintain a high grade
of product. The tolerances on the diameters of internal threads
are plus, being applied from the minimum sizes to above the minimum
sizes. The tolerances on the diameters of external threads are minus,
being applied from the maximum sizes to below the maximum sizes.
The pitch diameter tolerance for internal or external threads for
any given class is the same.
Below are examples of the proper nomenclature for single and multi-start
Centralizing Acme Threads:
Single Start: 1.250"-5 ACME-2C or 1-1/4"-5 ACME-2C
1.250-inch major (nominal) diameter, 5 threads per inch, single
thread, Class 2C fit, Right Hand
Multi-Start: 2.750"-0.4P-0.8L-ACME-3C or 2-3/4"-0.4P-0.8L-ACME-3C
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double
thread, Class 3C, Right Hand.
Single Start: 1.250"-5 ACME-2C LH or 1-1/4"-5 ACME-2C
LH
1.250-inch major (nominal) diameter, 5 threads per inch, single
thread, Class 2C fit, Left Hand
Multi-Start: 2.750"-0.4P-0.8L-ACME-3C LH or 2-3/4"-0.4P-0.8L-ACME-3C
LH
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double
thread, Class 3C, Left Hand
Notice:
This website is funded by the sale of screw thread measurement tools. It will help us continue to offer this data if you allow us to have the opportunity to sell our tools to your company. If you find this information useful, please work to get Gage Crib Worldwide Inc. on the bid list for future purchases of screw thread measurement tools.
Disclaimer:
This data is provided for general information only. The intention
is to provide accurate information; regardless; errors may exist
in the supplied information. If accuracy is critical, base your
final decisions on the data provided in the root document: ANSI/ASME
B1.5; which is a copyrighted document. To purchase a copy visit
an Authorized Reseller.
Comments:
Original Posting: 7/14/2009
Last Revision: 5/15/2020
Error corrections in, or comments about, the above data can be sent
to: office@gagecrib.com
Gage Crib Worldwide, Inc.
6701 Old 28th St SE, Suite B
Grand Rapids, MI 49546-6937
Phone: 001-616-954-6581 • Fax: 001-616-954-6583 CONTACT FORMS & INFO
