Ball Splines: selection entry, structure, preload P0/P1/P2.
Start from the selection guide, then dig into structure and preload.
A ball spline lets one shaft carry torque and linear motion at the same time: the outer race slides freely along the shaft while still transmitting torque to or from it. Typical cases are axes that must rotate while extending — robot Z-R axes, indexing heads, winding traverse units.
Doing the same with a screw plus a guide needs two mechanisms; a spline merges them into one shaft and saves space.
| Type | Structure | Mounting | Use |
|---|---|---|---|
| SLF (flanged) | Race with mounting flange | Bolted straight to the plate, compact radially | When rotary output mounts to a face plate |
| SLT (cylindrical) | Plain cylindrical race | Held by a housing or cover, axial position adjustable | When it sits in a bearing block or gearbox |
Fix the mounting method first, then shaft diameter and length. Choosing the other way round regularly produces a race that cannot be mounted.
This is the most common mistake: spline preload is P0/P1/P2, a separate system from the screw's ZF–Z3. Do not carry one across to the other.
| Preload | Meaning | Use |
|---|---|---|
| P0 | No preload (clearance) | Minimum sliding resistance, low positioning demand |
| P1 | Light preload | General industry, stiffness with free sliding |
| P2 | Medium preload | High torsional stiffness, minimal clearance |
Similarly, linear guide accuracy is N/H/P/SP/UP while screw accuracy is C3/C5/C7/C10. Three separate code systems, not interchangeable.
A spline has to clear two sets of ratings:
When the race carries radial load or a moment, that side must be checked too. Verifying torque alone is how early failures get missed.
BSHR is a threaded ball screw — it belongs to the screw range, not to ball splines. Sizing it as a spline gives you the wrong torque figures and the wrong mounting dimensions.
Two other useful equivalences: catalog SFH matches our SFA, and SFNU05020-4 = SFU05020-4 = DFU05020-4 are the same screw under different naming.
A screw converts rotation into linear feed. A spline lets a shaft rotate while sliding freely along its axis. Use a spline when the axis must turn and extend at once, such as a robot Z-R axis; use a screw for plain feed.
Splines and screws use separate standards. Screws are ZF/Z0/Z1/Z2/Z3, splines are P0/P1/P2. Carrying one system across to the other gives stiffness that does not match reality.
SLF is flanged and bolts straight to a plate with a small radial envelope. SLT is cylindrical and needs a housing or cover, with adjustable axial position. Decide the mounting method first.
No. BSHR is a threaded ball screw in the screw range. Sizing it as a spline gives mismatched torque ratings and mounting dimensions.