The choice between single-nut and double-nut ball screws revolves around the trade-off between cost/compactness (Single-Nut) and precision/rigidity (Double-Nut).
1. Single-Nut Ball Screw
A single-nut design consists of a screw shaft and a solitary nut body. If preload is required, it is typically achieved by inserting slightly oversized balls into the raceway.
Cost-Effective: With fewer components, these units are significantly more economical to manufacture and purchase.
Compact Footprint: The nut length is much shorter than a double-nut assembly, conserving installation space and maximizing effective stroke length.
Low Friction: Single nuts generally exhibit lower internal friction (torque), resulting in smoother operation and reduced heat generation.
Applications: Ideal for general transport systems, XY tables, 3D printers, and light-duty automation where extreme stiffness is not the primary requirement.
2. Double-Nut Ball Screw
A double-nut assembly consists of two nut halves mechanically tensioned against each other, usually via a precision spacer or spring.
Zero Backlash: The tension between the two nuts completely eliminates axial play. This ensures immediate response when reversing direction, with no "dead zone" or lost motion.
High Rigidity: The mutual preload between the nuts creates a highly rigid structure that resists deformation under heavy cutting loads or rapid acceleration, thereby minimizing vibration.
Superior Accuracy: The combination of zero backlash and high stiffness results in exceptional positioning accuracy and repeatability.
Applications: Essential for precision CNC machine tools, grinding machines, and heavy-duty industrial robots requiring exact positioning.