8 min read · 7 Apr 2026 · SLS Engineering Team
CNC Spindle Bearing Selection — Angular Contact Sets and Preload
Sizing spindle bearings for accuracy, thermal stability and the right preload.
A CNC spindle is essentially a bearing arrangement holding a tool. Get the bearings wrong and the part profile drifts within the first thermal cycle.
Common arrangements
- DB (back-to-back) — high stiffness, accommodates moment loads. Standard for milling spindles.
- DF (face-to-face) — accommodates misalignment between bearing seats; rare on machine tools.
- DT (tandem) — for unidirectional axial loads.
- Triple or quad sets (DBD, DBB, QBC) — heavy-duty milling.
Choosing contact angle
| Angle | Use |
|---|---|
| 15° (C) | High speed, low axial: grinding spindles, finishing |
| 25° (AC) | Balanced milling spindles |
| 30° (A) | Heavy axial: drilling, threading |
Preload class
Most machine tool manufacturers use GA (light) or GB (medium) preload sets. Heavier preload increases stiffness but generates heat — never upgrade preload class without recalculating temperature rise.
Lubrication
- Grease (Kluber Isoflex NBU 15) — re-lube-free for spindle speeds up to n × dm 1,000,000
- Oil-air — for ndm 1,500,000+
What to share when ordering
- Spindle bore (mm) and existing part number, e.g. 7014 CTSULP4
- Maximum operating RPM
- Tool taper (BT, HSK, ISO)
- Coolant exposure (mist, flood, MQL)
SLS stocks NSK, SKF and FAG matched super-precision sets ready for same-day dispatch from Mumbai.
Talk to SLS Bearings India
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