베어링 끼워맞춤, 헐거우면 "크리프", 너무 조이면 "수명 단축"

Bearing fit is one of the most frequently misdesigned aspects of mechanical assemblies. Too loose causes creep that damages housings; too tight eliminates internal clearance and drastically shortens bearing life.

1. Golden Rule: Interference Fit for the Rotating Ring

• Inner ring rotates (motors, gearboxes): Inner ring → shaft with interference (k5, m5, n5); Outer ring → housing with clearance/transition (H7, JS7)
• Outer ring rotates (wheels, rollers): Outer ring → housing with interference (K7, M7, N7); Inner ring → shaft with clearance (g6, h6)

The stationary ring always receives load at the same point (no creep risk), while the rotating ring receives load at continuously changing points — hence requires secure interference.

2. Load Magnitude vs. Interference

• Light load (C/P ≥ 15): k5, m5 — light motors, precision instruments
• Normal load (C/P = 8–15): m5, n5 — general reducers, conveyors
• Heavy load (C/P ≤ 8): n5, p5, r5 — rolling mills, crane drums

3. Most Common Fit Combinations

• General motor / gearbox: Inner k5 / Outer H7
• High-precision spindle: Inner js5 / Outer JS6 (preload adjustable)
• Self-aligning (large shaft): Inner m6 / Outer H8

4. Check Internal Clearance Reduction

Interference fit reduces bearing internal clearance. If too small, thermal expansion during operation drives clearance to zero, causing catastrophic life reduction. When interference is large, select C3 or C4 clearance group bearings to maintain sufficient operating clearance.