Acme Lead Screw Advantages and Features
Roton’s rolled thread Acme lead screws and high performance Acme nuts are combined to provide the optimum performance available in this type of lead screw. The highly burnished surface finish of the acme screw and low friction bronze and plastic acme nuts yield a smoother, less abrasive action than conventional cut Acme screws or lead screws. Improved wear and surface properties insure users a longer service life and quieter operation, requiring less power in a wide variety of applications.
Materials and Processes
All Acme lead screws, 1 3/4 inches in diameter and larger, are made of special quality medium carbon steel. Acme lead screws smaller than 1 3/4 inches are made from special quality low carbon steel. Sizes with Material listed as “Stainless Steel” (on the Acme Screw Data and Part Numbers page) are made from 304 type stainless steel. Alternate acme lead screw materials are aluminum alloys, other stainless grades, and high machinability grades of carbon steel. (For more information on materials see Table 35)
Acme lead screws are cold formed using a unique, highly accurate thread rolling process which guarantees a smooth, accurate, high quality thread. Our thread rolling process eliminates the interrupted grain flow of conventional cut threads, thereby increasing yield, ultimate, and fatigue strengths.
Acme Lead Screw Selection
With over 60 sizes in right and left hand versions, Roton offers the most complete Acme lead screw product selection in the industry. Standard acme nuts are offered in bronze, plastic and steel. Bronze and plastic acme nuts are offered in universal sleeve style and in threaded mount style for mating with steel flanges. Stainless steel acme hex nuts are offered in most sizes. Round, square, and hex nuts are offered in carbon steel. See Tables 5, 6, 7, 8, 9, and 10 for screw and nut part numbers and other detailed information.
All acme lead screws are furnished with a plain, oil dip finish. Screws may be electroplated, but use of stainless steel is encouraged for corrosive environments because electroplated surfaces are the first to wear off in use. Also, electroplating requires very close process control to avoid fit-up problems with mating nuts. Without extremely accurate control, the thickness of plating can vary greatly over the length of the screw shaft. Users intending to electroplate are encouraged to review Roton Engineering Bulletin No. 963 which discusses the plating process in detail. Black oxide finish is also available.
All acme steel nuts are furnished with a plain, oil dip finish. Nuts may be electroplated; however, the same plating precautions that apply to acme lead screws apply to nuts. Nuts, having a shorter length of engagement, are not as susceptible to electroplating thickness variations.
Design Considerations for Rolled Acme Lead Screws
Most applications can be satisfied by selecting from the stock sizes listed. However, OEMs may find an optimum design solution requires a special size or special features such as stub series threads, special diameter and lead combinations, metric Trapezoidal threads, etc. For these applications, Roton is uniquely qualified with over 30 years experience in serving the OEM market.
Extensive tooling and software resources can be utilized to assist the OEM designer in finding the very best solution for any application. Contact Roton Application Engineering for more details.
Acme Nut Selection
When selecting the right acme lead nut for an application, there are a few things to keep in mind. Bronze acme lead nuts provide superior service at high working loads. They should be well lubricated with a good quality Extreme Pressure (EP) grease compatible with the operating environment. Plastic acme lead nuts can be used without lubrication and are popular with stainless steel Acme lead screws for wash-down applications. Steel nuts should be used for limited duty mainly to sustain loads rather than to move loads. Without lubrication, steel nuts may gall to steel screws. These nuts are the least costly and are used where low initial cost is of prime importance.
Application engineering information is available from Table 4. Additional engineering information is available in the Application Engineering Section. Those designers not familiar with power screw applications are encouraged to review this section as well.
Self-Locking Lead Screws
All Acme series lead screws are single start and have lead angles of 5° or less, and will not backdrive under most conditions. This self-locking feature eliminates the need for brakes or other holding devices to sustain loads after they have been positioned. All other power screws including Ballscrews, Hileads(r) and Torqsplines(r) may require some braking means to prevent backdriving.
All sizes of Acme lead screws are made in large volume and their widespread popularity makes them the least costly of all power screws.
Acme Lead Screw Efficiency
Mechanical efficiencies for Acme lead screws range from 20% – 40% depending upon the lead angle, coefficient of friction and nut material. Plastic acme nuts offer approximately 10% – 20% better efficiency than bronze acme nuts because of their lower coefficient of friction when running against steel screws.
Mechanical Advantage of Acme Lead Screws
Low lead angles offer a high mechanical advantage for Acme series lead screws. This means they require less input torque for a given load than other types of power screws. The finer the threads for any given diameter, the greater the mechanical advantage.
Typical Applications for Acme Lead Screws
Roton’s Acme lead screws and acme nuts are widely used and well suited for both manual and power drive applications including:
- machinery slide drives
- shop & office table lifts
- valve stems
- medical device drives
- farm machinery
- scaffolding support legs
- trailer jacks & jackstands
- general purpose jacks
- screw press drives