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The World of ACME Screw Threads

The World of ACME Screw Threads
In my younger days I thought ACME was the name of a company that brought Wile E Coyote the newest innovations on how to catch a Roadrunner, but as I have grown older I realize ACME is an important screw thread found in daily use in many places.
Photo of General Purpose ACME Threaded Rod
In the mid 1890's, various versions of square screw threads were used for the purpose of power transmission by producing traversing motion. This is a very valuable function in machines.
Extensive engineering effort was applied to the power transmission screw thread design and the 29° thread form was found to be the ‘best’ included angle to use. Not 28°, or 30°, but specifically 29°. It provided a screw thread which was easier to machine and had optimal properties for power transmission. Thus, the term ACME was applied to the 29° included angle screw thread form. The word ACME as defined by Merriam-Webster as the peak, the one that represents perfection of the thing expressed. So, if we take the definition for what it is, when it comes to power transmission screw threads, the ACME screw thread is the best thing going.
When created prior to 1895, ACME screw threads were designed to replace the difficult to manufacture square threads, and variations of square threads. Today ACME screw threads are extensively used for a variety of purposes. Long-length ACME screw threads are used for controlled movements on machine tools, testing machines, jacks, aircraft flaps, and conveyors. Short-length threads are used on valve stems, hose connectors, bonnets on pressure cylinders, steering mechanisms, and camera lens.
The problem is that the ACME screw thread can be a pretty confusing screw thread to deal with if you're not sure what you're looking at. I hope to clear it up for you in this page, and its linked pages.
There are 3 different forms of ACME Screw Thread: General Purpose, Centralizing, and Stub ACME.
General Purpose ACME Screw Threads and Centralizing ACME Screw Threads are defined in ANSI/ASME B1.5.
Stub ACME Screw Threads are defined in ANSI/ASME B1.8.
While the three different variations of the ACME screw thread are not all listed in the same standard, they do share some similar characteristics. All three styles of ACME screw threads have 29° included angle; all are perceived as a bilateral transverse motion screw thread; all offer high strength with ease of machining and assembly; and all are largely used for feed and adjusting screws.
One thing to note is that the term ACME, when being used to define screw threads, is codified to be used only for 29° included angle. Referring to screw threads with included angles other than 29° is improper and may lead to engineering/manufacturing confusion. A more appropriate term should be identified, other than ACME, if the angle is not 29°.
One very common screw thread form, which is almost identical to ACME is the Trapezoidal Screw thread (the Tr-series). The Trapezoidal screw thread is sometimes called: Metric ACME; European ACME; German ACME. None of these designations is proper nor accepted by the standards (DIN 103; DIN 38; DIN 263; DIN 30295; DIN 6063). The Trapezoidal screw thread and the ACME screw thread are visually identical, used in similar applications, and only through careful measurement will you find the differences. Trapezoidal screw thread has a 30° included angle where ACME screw thread has 29° included angle. Trapezoidal screw thread is made and measured in millimeters where the ACME screw thread is made and measured in inches. Trapezoidal screw thread pitch is stated in millimeters of pitch where ACME screw thread pitch is stated in threads-per-inch.
General Purpose ACME Screw Threads defined in ANSI/ASME B1.5 is for, like its name suggests, general purpose usage. Read more…
STUB-ACME Screw Threads are defined in ANSI/ASME B1.8. This version of the ACME thread has been truncated, shortened, ‘stubbed’, for use in a smaller space. There are many authorized variations of the STUB-ACME form. Read more...
Centralizing ACME Screw Threads are defined in ANSI/ASME B1.5. There are specific set of conditions where this version of ACME is desired, but there are more details to monitor in its manufacturer. Read more…
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.
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 documents: ANSI/ASME B1.5 and B1.8; which are copyrighted documents.
To purchase a copy visit an Authorized Reseller.
Original Posting: 12/9/2008
Last Revised: 5/13/2020
If you discover error or wish to comment on this page contact Wayne at:office@gagecrib.com
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