Bearing size mismatch causes 30% of unplanned downtime in rotating industrial equipment. The core solution is matching bore diameter to shaft specs and outer diameter to housing constraints, with precise load calculations to avoid over-sizing or under-sizing.

How to Calculate Required Bore Diameter

Bore diameter interfaces directly with the shaft, requiring controlled clearance (typically H7 tolerance for general use). A 20mm shaft needs a 20H7 bore, allowing 0 to +0.021mm clearance for smooth rotation. For shafts with radial load >5kN, add 10% to the calculated bore to handle heat-induced expansion. MS Bearings provides a quick bore size chart for conveyors and pumps, plus a free online tool for size validation based on shaft load and RPM.

Avoid Common Size Mismatch Mistakes

• Assuming bore size matches shaft diameter without clearance: Causes binding at high RPM, cutting bearing life by 40%.
• Ignoring outer diameter limits: A 6205 bearing has a 52mm outer diameter; fitting it in a 50mm housing leads to deformation.
• Overlooking thermal expansion: For bearings operating above 80°C, add 0.05mm to prevent seizure.

Key Parameters to Validate Bearing Size

Outer diameter depends on housing capacity and load distribution. A 1500 RPM fan bearing with 8kN radial load works best with a 6307 bearing (35mm bore, 80mm outer diameter). Check dynamic load rating: it must handle 1.5x operating load for reliability. Static load rating is critical for shock loads (e.g., construction equipment), needing 2x static force. Cross-reference with DIN ISO standards to confirm compliance.

For project-specific bearing sizing, consult your supplier. Contact MS Bearings for free technical support on custom size adjustments.

What tolerance grade is standard for industrial bearing bores?

Standard is H7 for general applications, balancing fit and rotation smoothness. For high-precision CNC machines, use H5 tolerance to minimize radial runout.