The term lead screw is used to describe a system that translates rotary or turning motion into linear motion. The assembly is usually a screw shaft combined with a nut.
There are a number of factors to consider when selecting a lead screw for your application. One of them is the pitch, which is how far from the peak of one thread to the next.
Trapezoidal Thread Profile
Acme lead screw are a type of precision screw thread that has a trapezoidal form factor. They are comparatively easier to manufacture than square threads and provide high accuracy.
A trapezoidal thread profile consists of two major diameters, which correspond to the crest of a male or female thread root. It also includes a minor diameter, which is the minimum diameter of an imaginary circle that makes contact with the crest of a male or female root.
A trapezoidal lead screw threads are generally available in metric sizes. They are commonly used for power transmission applications because they offer more strength than their equivalent square thread counterparts.
They are manufactured using multiple-start threads, left-hand turning threads, and self-centering threads. These threads typically do not bind under lateral forces, which helps reduce wear. They are also less likely to loosen or back up under load than Metric Precision Acme lead screws and nuts. They operate with minimal backlash (play) and can be compatible with most types of nut and screw assemblies.
Self-Locking
A self-locking power screw is a type of lead screw that does not allow the load to lower without an external force applied. This feature makes it a great choice for applications that require the screw to hold its position until the torque is applied.
In some applications, self-locking leadscrews are used to produce high accuracy in precision machinery. They also reduce maintenance costs by eliminating lubrication, a common issue with other types of power screws.
Acme lead screws are available in a variety of nut materials, lubrication types and lead and thread forms. Choosing the right specifications for your application is key to maximizing efficiency and achieving optimal performance.
Acme screws offer efficiencies of 20 to 80 percent, depending on the type of lubrication and material selection. They are also quieter than ball screws, and can operate in harsh operational environments.
Low Friction
Acme lead screws are known for their low friction and high mechanical efficiencies. This is primarily attributed to the trapezoidal thread profile, low lead angles and nut material selection.
Nuts are made from a variety of materials, including polymers, self-lubricating plastics and metals such as bronze or brass. Depending on the type of nut material, acme screw efficiencies range from 20% to 40%.
When choosing an acme lead screw, you must consider operating load, speed, accuracy, power requirements and environment. In addition, you must select a suitable lubricant for maximum performance.
Stainless steel acme nuts are also available in most sizes for use in corrosive environments. Plain, oil dip finish screws are offered with a black oxide coating for a corrosion-resistant surface.
High Efficiency
Acme lead screws are one of the most efficient power screw designs available for many linear motion applications. They also provide a high level of operational safety and repeatability.
This feature is due to the self-locking nature of their thread form. This eliminates the need for brakes or other holding devices to sustain loads after they have been positioned.
The nut material selected for an acme thread lead screw can make a significant difference in its efficiency. Plastic acme nuts offer about 10%- 20% better efficiency than bronze acme nuts because of their lower coefficient of friction running against steel screws.
Nook offers several acme screw options in both rolled and milled forms for the best performance. Rolled threads are stocked for quick delivery while the milled process allows for more flexibility with journal machining.
