Introduction
Selecting the right ball screw is one of the most consequential decisions in CNC machine tool design and maintenance. A ball screw converts rotary motion to linear motion with minimal friction, and the accuracy grade you choose directly determines your machine positioning precision, surface finish quality, and long-term reliability.
Two primary manufacturing methods dominate the market:
grinding and
rolling. Understanding the difference between these processes and when each is appropriate can save thousands of dollars while ensuring your machine meets performance requirements.
Precision Grades: C2 vs. C3 vs. C5 vs. C7
Ball screw accuracy is defined by
lead tolerance - the maximum deviation from nominal travel over a specified length:
| Grade | Lead Tolerance (per 300mm) | Typical Process | Primary Application |
|---|
| C2 | ±5 μm | Ground | High-precision CNC, measuring machines |
| C3 | ±8 μm | Ground | CNC machining centers, precision automation |
| C5 | ±18 μm | Ground or Rolled | General CNC, industrial automation |
| C7 | ±50 μm | Rolled | Transport systems, positioning tables |
When C2/C3 Ground Screws Are Necessary
1. Sub-micron positioning - Semiconductor lithography, CMM machines require C2 accuracy
2. Surface finish requirements - Aerospace and mold-making where Ra 0.4 um depends on vibration-free motion
3. Thermal stability - Tighter tolerances exhibit more predictable thermal expansion
When C5/C7 Rolled Screws Are Sufficient
1.
General automation - Pick-and-place, packaging machines where ±50 um tolerance is acceptable
2.
Cost-sensitive projects - When accuracy does not justify the 3-5x price premium of ground screws
3.
High-volume OEM - Large quantities where rolled screws provide adequate performance
Selection Guide: Matching Ball Screw to Application
| Application | Grade | Process | Key Consideration |
|---|
| CNC milling center | C3 | Ground | Positioning accuracy ±0.01mm |
| CNC lathe Z-axis | C3–C5 | Ground | Moderate precision, high rigidity |
| EDM machine | C2–C3 | Ground | Mirror-finish surface requirement |
| Robotic arm | C5–C7 | Either | Speed and repeatability |
| Packaging machine | C7 | Rolled | Cost-effectiveness |
| Semiconductor equip | C2 | Ground | Sub-micron positioning critical |
| Medical devices | C2–C3 | Ground | Precision and cleanliness |
Material and Diameter Considerations
-
Shaft diameter - 8mm to 100mm; larger diameters for greater rigidity
-
Ball nut type - Single nut for compact designs, double nut for higher rigidity
-
Lead (pitch) - Higher lead means faster travel but lower resolution
-
Material - Induction-hardened SCM420 (HRC 58-62) for both types
Luoyang Songju Ball Screw Solutions
Luoyang Songju manufactures precision ball screws across five series - FC, FCD, FY, FYB, and FYD - covering both ground and rolled types in C2, C3, C5, and C7 accuracy grades. Our 8-100mm diameter range serves applications from compact automation to heavy-duty CNC machining centers.
Every ball screw undergoes 100% pre-shipment inspection, including lead accuracy measurement, surface finish verification, and dynamic torque testing. Our ISO 9001:2015 certified facility combines precision grinding with competitive China-manufactured pricing.
Ready to select the right ball screw? Contact our engineering team or
browse our full product line.
