In industrial automation and precision equipment, trapezoidal lead screws are the core transmission mechanism for achieving rotary-to-linear motion, directly affecting the accuracy and stability of the equipment. However, practitioners often suffer from decreased equipment efficiency and shortened lifespan due to a lack of in-depth understanding of the principles and improper selection. This article will break down the motion principle of trapezoidal lead screws and provide a practical selection guide. I. Product Motion Principle and Related Parameters 1. Motion Principle: The trapezoidal lead screw converts rotational motion into linear motion through the meshing of the screw and nut, simultaneously transmitting energy and power. II. Product Features 1. Simple structure, convenient processing and operation, and economical cost; 2. Self-locking function is achieved when the thread helix angle is less than the friction angle; 3. Smooth and stable transmission process; 4. Relatively high frictional resistance, with a transmission efficiency in the range of 0.3~0.7. In self-locking mode, the efficiency is below 0.4; 5. Possesses a certain degree of impact and vibration resistance; 6. Overall load capacity is stronger than that of ordinary rolling screws. III. Selection and Verification Calculations For general force-transmitting screws, the main failure modes are thread surface wear, fracture under tensile stress, shearing, and shearing or bending at the thread root. Therefore, the main dimensions of the screw drive are determined primarily based on wear resistance and strength calculations during design. For transmission screws, the main failure mode is excessive clearance due to wear or deformation leading to decreased motion accuracy. Therefore, the main dimensions of the screw drive should be determined based on thread wear resistance and screw stiffness calculations during design. If the transmission screw also bears a large axial load, its strength needs to be additionally calculated. Long screws (slenderness ratio exceeding 40) that are not manually adjustable may produce lateral vibration; therefore, their critical speed needs to be checked. IV. Usage Precautions 1. Load Considerations: Additional radial loads should be avoided as much as possible, as such loads can easily cause screw malfunction, increased wear, and jamming. 2. Dust Prevention Requirements: Foreign objects must be prevented from entering the thread. If impurities such as iron filings, tin dross, and aluminum shavings are easily generated under operating conditions, a protective cover should be installed to prevent foreign objects from entering the thread and causing abnormal wear or jamming. 3. Slenderness ratio requirement: When the slenderness ratio exceeds a certain range (60 or above), the screw will bend due to its own weight, resulting in radial off-center load on the nut. Depending on the actual operating speed and torque, this may lead to abnormal wear, jamming, shaft end bending, or even breakage. To solve this problem, an anti-runout device can be installed in the middle of the screw for constraint. 4. During installation, attention should be paid to the coaxiality and levelness calibration of the fixed-support installation method; for the fixed-free cantilever structure, attention should be paid to the control of shaft end tolerances and the locking and reinforcement of the head. 5. When installing a trapezoidal thread screw, runout verification must be performed. If suitable measuring equipment is lacking, the screw can be moved by hand along its entire length once or multiple times before installing the driving component. If the force required to move the outer diameter of the shaft is uneven and accompanied by wear marks, it indicates that the lead screw, nut support, and guide rail are not aligned. In this case, first loosen the relevant mounting screws, and then move the lead screw by hand once. If the required force becomes uniform at this time, the corresponding components can be recalibrated. If the force is still uneven, the mounting screws need to be loosened again to determine the location of the calibration error.