Ground-Thread Bearing
Lock Nut Seats

A lock nut seat is the threaded section of a shaft that engages a bearing lock nut (KM series) to axially retain and preload the bearing inner race. The thread must be ground (not cut) to ISO 4 class for precise bearing preload control. The face runout of the lock nut seat shoulder must be ≤ 0.005 mm — a tilted nut face applies non-uniform axial load to the bearing inner race, causing uneven preload distribution.

Bearing lock nut threads (KM series per DIN 981) require ISO 4 class thread accuracy — pitch error ≤ 0.004 mm/25 mm, flank angle ≤ 5′, thread OD tolerance 4h. This accuracy is only achievable by thread grinding — cut threads have too much pitch error to provide consistent bearing preload. HXC grinds KM-series lock nut threads to ISO 4 class on all precision spindle and bearing shaft orders.

The KM (or KMT) series is the ISO/DIN standard for bearing lock nuts used on precision shafts. KM nuts feature a fine metric thread (e.g., M30×1.5, M40×1.5) with a lock washer (MB series) or integrated locking feature. The nut is tightened against the bearing inner race to set axial preload, then locked with the washer to prevent loosening during operation. HXC machines KM-series lock nut seats on stepped shafts, spindles, and rotor shafts.

The bearing face of the lock nut seat — the shoulder that the bearing inner race bears against — must have runout ≤ 0.005 mm to the shaft axis (measured with a dial indicator while rotating the shaft). A tilted seat face applies a bending moment to the bearing inner race, causing non-uniform loading across the ball complement and accelerating fatigue. For ultra-precision spindle applications, ≤ 0.002 mm is required.

Prototype (1–5 pcs, turned + thread ground): 4–7 days. Small batch (10–50 pcs): 7–12 days. Production (100–1,000 pcs): 10–16 days. Stainless or titanium: add 2–4 days. Rush production available.

42CrMo4 (induction hardened) for industrial and automotive. 20CrMnTi (carburized) for maximum surface fatigue. SUS303/316L/440C stainless for food, pharma, marine, clean-room. Al 6061/7075 hard-anodized for lightweight. Ti Grade 5 for aerospace/medical.

Standard ground OD / journal: Ra 0.4 µm. Precision bearing seats: Ra 0.2 µm. Seat face: Ra 0.4 µm and runout ≤ 0.005 mm. All measured by contact profilometer and reported on the inspection certificate.

Yes — keyways, splines, MB-washer keyway slots, cross-holes, flats, and tapers are all machined in the same 5-axis turning-milling setup, ensuring concentricity between all features within 0.003 mm TIR. The lock-washer keyway is positioned to DIN 5406.

Match the KM nut to the shaft thread: KM5 = M25×1.5, KM6 = M30×1.5, KM7 = M35×1.5, KM8 = M40×1.5 (per DIN 981). The matching MB lock washer (MB5–MB8) has an inner tab that drops into a keyway in the shaft and an outer tab that bends into a slot in the nut. Specify the nut series and HXC machines the matching thread and washer keyway.