Structure of ball spline

Ball spline is a precision mechanical component widely used in applications that require simultaneous transmission of torque and allow linear motion, such as machine tools, robots, and automation equipment. Its structural design is exquisite, combining the characteristics of high rigidity and low friction. The following is a detailed breakdown of its structure:
1. Outer cylinder (spline nut)
Structure: It is usually a cylindrical metal shell with precise spiral or straight grooves machined inside, forming a ball track corresponding to the grooves of the spline shaft.
Function: Fixed to the equipment base, installed through flanges, threaded holes or bolt holes, providing structural support. The internal groove cooperates with the shaft to guide the movement of the ball bearings.
Material: High carbon chromium bearing steel (such as SUJ2), quenched and ground to ensure wear resistance and accuracy.
2. Spline shaft
Structure: A precision shaft with straight or spiral grooves on the surface that match the outer cylinder, usually subjected to ultra precision machining to reduce friction.
Function: Transmit rotational torque or linear thrust, and achieve low resistance relative motion with the outer cylinder through ball bearings.
Material: Similar to the outer cylinder, hardened steel is used to improve its lifespan, and ceramic coating may be used in some high load scenarios.
3. Ball bearings
Structure: High precision steel balls (commonly 1-10mm in diameter), graded according to ISO standards (such as G5 grade) to ensure dimensional consistency.
Function: Rolling between grooves, bearing radial and axial loads, reducing friction, and achieving efficient power transmission.
Arrangement: Multiple column design (such as 2-4 columns) to enhance load capacity, eliminate gaps through pre tightening, and improve rigidity.
4. Retainer (holder)
Structure: A frame made of nylon, metal (copper or steel), or composite material, separating ball bearings and maintaining uniform spacing.
Function: Prevent ball collision, ensure smooth circulation, reduce wear and noise, especially crucial in high-speed motion.
5. Loop Path
Design: The outer cylinder integrates a reflux channel (such as end cap or conduit type) to form a closed loop, allowing the ball to automatically return to the starting point after reaching the end of the track.
Function: Supports infinite continuous motion, suitable for long stroke applications, similar to ball screws but allows for rotational and linear compound motion.
6. Sealing and dust prevention
Sealing element: made of rubber or polyurethane material, located at both ends of the outer cylinder, to block the intrusion of pollutants such as dust and cutting fluid.
End cap: A metal or plastic cover plate that fixes the internal structure and assists in sealing, with some designs incorporating sealing lips to enhance protection.
7. Lubrication system
Oil injection hole/grease nozzle: Regularly add lubricating grease (such as lithium based grease), and some high-end models are equipped with self-lubricating modules or sealed lubricating grease.
Lubrication groove: The groove is designed with an oil storage structure to extend maintenance cycles and is suitable for environments with high cleanliness requirements.
8. Install interface
Types: Flanges (ISO or JIS standards), threaded holes, set screws, etc., suitable for different mechanical layout requirements.
Customization: Some applications require customized flange shapes or mounting holes to match specific equipment structures.