Acme Screw Sizes: Standard Specifications For Precise Applications

Acme screws are the preferred choice for linear motion applications. They are used for converting rotary motion into linear motion and are known for their quiet operation, affordability, precision, and low maintenance. Acme screws come in a variety of sizes, with diameters ranging from 1/8 inch to 6 inches and leads from less than 1/32 inch to 4 times the diameter. The standard thread angle for acme screws is 29 degrees, although smaller sizes may have a 40-degree angle. There are three classes of general-purpose acme threads: 2G, 3G, and 4G, each providing clearance for free movement. Acme threads are designed for transversal motion and are commonly used in vises and jack screw applications.

General Purpose ACME

When designing with ACME screw threads, it is recommended to use external and internal threads of the same class and type. The thread pitch of ACME screws is measured in TPI (Threads per Inch), which is the number of thread crests in 1" of threads.

ACME screws are a popular choice for linear motion applications due to their quiet operation, affordability, precision, and reduced maintenance requirements compared to alternative options. They are also diverse, with a wide range of diameters, lead sizes, end machining options, thread types, coatings, and materials to choose from.

Centralizing ACME

The class-of-fit for Centralizing ACME allows for tighter tolerances on all diameters, reducing the chances of the nut thread wedging on the screw. This is in contrast to General Purpose ACME, which has a standard amount of clearance in the thread form. The General Purpose ACME is the most common type, with a 29-degree angle (40-degree angle in smaller sizes) and a series of diameters and related pitches.

When choosing between Centralizing ACME and General Purpose ACME, it is important to consider the specific requirements of the application. Factors such as accuracy, size constraints, and the need for tighter tolerances and reduced clearance will influence the decision. Additionally, the end product, materials, and coatings should also be considered to ensure the best choice for the product design and engineering process.

Stub ACME

Acme screw threads are used for a variety of purposes, including controlled movements on machine tools, testing machines, jacks, aircraft flaps, and conveyors. The ACME thread was developed to offer better strength than a V-form, while overcoming the problems with the square thread form. The flank angle is 29°.

Acme thread pitches

The General Purpose ACME Screw Thread has a 29-degree included angle and a range of diameters and related pitches. The specific diameter and pitch are chosen based on the application's requirements, aiming to minimise the number of inventory items. The thread depth of a single-start Acme screw is typically half of the pitch, while stub acme threads have a lower profile with a thread depth less than the standard.

The Centralizing ACME thread is another variety, characterised by tighter tolerances and reduced clearance on the major thread diameter. This type of thread is designed to prevent the nut thread from wedging on the screw. Centralizing ACME threads are often used for feed screws, with examples including 2C, 3C, 4C, and 5C.

The Stub ACME thread is a third form, featuring a thread depth that is less than standard, resulting in a lower profile thread suitable for space-constrained applications. Acme lead screws offer a wide range of diameters and lead sizes, with diameters ranging from 1/8 inch to 6 inches and leads from less than 1/32 inch up to 4 times the diameter.

Acme thread forms

The General Purpose ACME Screw Thread has three classes: 2G, 3G, and 4G. Class 2G is the preferred choice for assemblies with internal threads fixed rigidly and movement of the external thread limited by its bearing or bearings. Classes 3G and 4G are recommended if less backlash or end play is desired. The ACME thread pitches are measured in TPI (Threads per Inch), which is determined by counting the number of thread crests in one inch of threads.

The ACME thread form is designed for transversal motion and is commonly used in vises and jack screw applications. It features wide trapezoidal thread crests that enable motion. The trapezoidal screw, with its 29-degree thread angle, efficiently converts rotary motion into linear motion, offering benefits such as quiet operation, affordability, precision, and reduced maintenance compared to alternative options.

The ACME lead screws are highly versatile, with diameters ranging from 1/8 inch to 6 inches and leads from less than 1/32 inch to 4 times the diameter. They can be customised with end machining, thread types, coatings, and materials. The choice of screw and nut materials should consider factors such as load, speed, duty cycle, operating temperature, chemicals present, accessibility, and maintenance interval. Common materials for lead screws include carbon steels, alloy steels, stainless steel, and titanium.

Frequently asked questions