How to select tolerances for holes and shafts that fit with bearings
The dimensional accuracy of bearings is constant, and the tolerance range is already established at the factory.
Taking the ordinary grade (P0 grade) 6308 bearing as an example, it can be found in the bearing tolerance table that the outer ring tolerance of the bearing is: upper tolerance: 0, lower tolerance: -0.011
According to the rotation and load-bearing mode of the bearing, the outer ring is generally fixed relative to the inner ring, and the load-bearing is fixed load-bearing, not the main load-bearing. Based on these contents, it can be found in the recommended fitting table for shell holes that for bearings using bearing seats, the recommended tolerance zone for shell holes is H8
H8 tolerance zone: upper tolerance+0.054, lower tolerance 0. indicates clearance fit, large clearance amount: 0.065, small clearance amount 0
Fit between bearing inner ring and shaft:
The tolerance of 6308 bearing inner ring is: 0 upper tolerance, -0.012 lower tolerance. Based on the rotating load and ordinary load of the inner ring, the recommended tolerance zone for shaft fit is: m5,+0.020 upper tolerance, 0.009 lower tolerance. Explanation: The large clearance is 0.020, and the large interference is 0.003
In summary, determining the fit between the bearing and the shaft, as well as the housing hole, can be easily obtained by querying a series of tables based on the rotation pattern, load size, and accuracy level of the bearing. Different collaborations are required, and adjustments can also be made based on the list.