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In automation equipment and precision machinery design, ball screws are core components for achieving precise linear motion. However, many engineers are confused by the different accuracy grades, such as C3, C5, and C7. Choosing a higher grade results in costly errors, while choosing a lower grade can affect equipment performance. Today, we’ll thoroughly explain ball screw accuracy grades to help you easily select the right one.
Ⅰ. What is an accuracy grade? The smaller the number, the more accurate it is.
The accuracy grade of a ball screw is a quantitative rating of its motion accuracy based on international standards such as JIS (Japanese Industrial Standards). The core metric is “target travel error,” which is the maximum allowable deviation between the actual travel distance and the theoretical value within a 300mm travel range.
II. Comparison of Mainstream Accuracy Grades and Application Scenarios
| Precision Grade | Manufacturing Process | Tolerance (within 300mm travel) | Key Features | Typical Applications |
|---|---|---|---|---|
| C7 (Rolled) | Rolled | ±50 µm | Standard precision, best price-performance ratio, most common in the market | 3D printers, packaging machines, general automation equipment, medical equipment, electric door controls |
| C5 (Ground) | Ground | ±18 µm | Medium-high precision, balanced precision and cost, industry leader | General CNC machines, injection molding machines, industrial robots, precision measurement equipment |
| C3 (Ground) | Ground | ±8 µm | High precision, high performance, good surface finish, temperature control requirements | High precision machining centers, semiconductor equipment, precision measuring instruments |
III. How to Choose the Right Lead Screw? Remember These 3 Points!
Blindly pursuing high precision will only increase costs. Follow these principles:
Based on Needs: Determine the positioning accuracy requirements of your equipment. A C7 grade is generally sufficient for a 3D printer, while a CNC milling machine requires at least a C5 grade.
Cost Consideration: Each increase in accuracy significantly increases costs. While ensuring performance is maintained, choose the most economical grade.
System Considerations: Lead screw accuracy is only one component of system accuracy. Bearings, guideways, servo motors, and even assembly processes are equally crucial. A high-precision lead screw paired with a substandard support will not perform to its full potential.
Choosing a ball screw’s precision grade is a wise balance between performance and cost.
Choose C7 for basic applications: economical and affordable.
C5 for industrial standards: precise and reliable.
Choose C3 for ultimate precision: unmatched accuracy.
We hope this guide will help you navigate the complexities and make the most informed choice for your next project. If you still have questions, please consult our technical experts for customized solutions.