1.What is the lead screw?

The screw is a mechanical transmission element mainly used to convert rotary motion into linear motion, or convert linear motion into rotary motion. Screws can be divided into many types according to their structures and functions, such as ball screws, sliding screws and planetary roller screws. Among them, the ball screw is particularly suitable for precision transmission due to its high precision, high efficiency and low friction resistance, while the sliding screw is an ordinary screw machine with a simple structure and easy manufacturing.

Lead screws are important components in a variety of industrial applications. They are responsible for converting rotational motion into linear motion and vice versa. There are different types of lead screws on the market, and choosing the right one can be quite challenging.

1.1 The structure and characteristics of the lead screw：

The screw is a threaded transmission device consisting of a screw and a nut. The screw is an axis component with equal pitch threads, and the nut is an internally threaded part. When the screw rotates, the threads of the nut on it move forward or backward, thereby achieving mechanical movement.
The main features of the screw are simple structure, high transmission accuracy, good reliability, and the ability to withstand large axial force and small radial force. Therefore, it is widely used in mechanical processing, machine tool manufacturing, automation equipment and other fields.

1.2 How the screw works

The working principle of the lead screw is explained by the laws of force and motion. When a torque is applied to the screw, the screw will rotate. At the same time, due to the thread engagement between the screw and the nut, the nut will also move accordingly, driving the working parts connected to the nut to move together, ultimately achieving mechanical transmission.

The transmission accuracy of the screw depends on the tightness and pitch of the screw thread. Generally, the smaller the pitch, the higher the transmission accuracy. In addition, the quality, processing accuracy and surface finish of the screw will also affect its transmission accuracy and lifespan.

2. Classification of screws

2.1 ACME screw

ACME screws are the type of screw used in industrial applications. It has a trapezoidal thread profile that provides high efficiency and stiffness. ACME lead screws have high load capacity and are ideal for heavy-duty applications. They are commonly used on CNC machines, lathes and milling machines.

 2.2. Ball screw

The core transmission principle of the ball screw is to convert rotational motion into linear motion and convert sliding friction into rolling friction. When the screw rotates relative to the nut, the rotating surface of the screw pushes the nut to move axially through the cyclic rolling of the balls, turning the rotation into linear motion; the rolling of the balls causes the sliding friction between the screw and the nut to change into the sliding friction between the balls, the screw, and the nut. The rolling friction between them turns sliding into rolling, greatly improving transmission efficiency. ​

The ball screw has high precision and high precision. They use a ball bearing assembly between the nut and screw to reduce friction, resulting in smooth and efficient operation. Ball screws are ideal for high-speed applications and are commonly used in the aerospace, automotive and medical industries.

2.3 Square thread screw

Square thread is a lead screw that offers many advantages in industrial settings. Its thread profile is designed to create a tight fit between the screw and nut for efficient motion transfer. Its sturdy construction makes it resistant to wear and tear, making it a reliable choice for applications with high loads and frequent use. With its precision machining and specialized design, square threads are critical to manufacturing processes that require precise positioning and movement.

2.4 Trapezoidal screw

Trapezoidal screws are similar to ACME screws, but have a different thread profile. The thread angle is 30 degrees compared to 29 degrees for ACME screws. This slight difference in angle provides greater load carrying capacity and efficiency. Trapezoidal screws are commonly used in industrial applications such as linear actuators, sliding doors and conveyor systems.

2.5 Power screw

A power screw is a lead screw that uses a nut and a rotatable screw to convert rotational motion into linear motion. They are commonly found in power transmission systems used to lift and lower heavy objects. Power screws are ideal for applications requiring high reliability and long life.

3. Application scenarios of lead screw

Lead screws are widely used in various mechanical equipment, such as CNC machine tools, machining centers, automated production lines, etc. The nut material is usually made of an internally lubricated polymer. Due to the high transmission accuracy of the screw, precision machining can be achieved, so it is also used in precision machinery, precision measurement and other fields. In addition, lead screws are also widely used in aerospace fields such as robots and space probes.

Some examples are laboratory and life science equipment such as DNA sampling, scanning and liquid handling equipment. Other applications include engraving, rapid prototyping, inspection and data storage. Lead screws are also used in heavy lifting applications when used in combination with metal (usually bronze) nuts.

4. The components of the screw are as follows:

• Screw Shaft: A screw shaft is a cylindrical rod that has a spiral groove or series of grooves along its length; this is called an external thread.
• Thread: The thread is the structure responsible for converting rotational motion into linear motion when the screw shaft and nut slide against each other.
• Nut: The screw nut is a cylindrical part whose internal threads match the external threads of the screw shaft.
• Major diameter: The major diameter is the maximum diameter of the thread. The major diameter of the screw shaft is the distance between two opposing tooth crests, while the major diameter of the nut is the distance between two opposing tooth roots.
• Minor diameter: The minor diameter is the smallest diameter of the thread. The minor diameter of the screw shaft is the distance between two opposing roots, while the minor diameter of the nut is the distance between two opposing tops.
• Top: The top is the convex helical structure in the external thread (screw shaft) and the depressed helical structure in the internal thread (nut).
• Root: The root is the concave helical structure in the external thread (screw shaft) and the convex helical structure in the internal thread.
• Thread Depth: Thread depth is the distance from root to crest, measured radially.
• Sides: The sides are the surfaces that connect the roots to the top.
• Pitch Diameter: The pitch diameter, or effective diameter, is located concentrically about halfway between the major and minor diameters. It is the diameter of an imaginary cylinder whose circumference intersects half the pitch.
• Pitch: The pitch is the axial distance between two adjacent threads measured parallel to the axis. It is equivalent to 1/number of threads per inch.
• Lead: Lead is the linear distance the screw shaft or nut travels along its axis in one complete revolution (3600 revolutions). As the lead increases, the linear speed also increases, but the load capacity of the screw decreases.
• Thread start count: The start count is the number of independent threads running around the thread length. The lead of a screw is determined by multiplying the number of independent threads by the pitch. Helix angle; Helix angle is the angle formed between the helix of the thread and a line perpendicular to the axis of rotation. Generally, a screw with a higher helix angle has less friction loss and therefore a higher efficiency, because for the same straight-line distance, the number of revolutions required to rotate such a screw is lower than that of a screw with a smaller helix angle. However, more torque is required to rotate the screw.
• Lead angle: The lead angle is the supplementary angle of the helix angle. It is the angle formed between the helix of the thread and a straight line parallel to the axis of rotation.
• Thread Angle: The thread angle is the angle formed between two adjacent threads.
• Thread handedness: Thread handedness refers to the direction of the thread along the length of the thread. The lead screw can be right-hand or left-hand. In right- and left-hand screws, the threads run around the length of the screw in a clockwise and counterclockwise direction respectively.

In short, as a kind of transmission device, the screw has the characteristics of simple structure and high transmission accuracy, and plays an important role in industry, technology and other fields.