Specifications for shafts and housing support surfaces

Shaft bearing seat

Recommended fits for bearings on solid steel shafts in cast iron housings are provided under Bearings, units and housings and in the SKF catalogue Rolling bearings.
If adapter or withdrawal sleeves are used, the sleeve seat on the shaft should be machined to tolerance class h9 or better. The total radial runout should be IT5/2 for tolerance class h9.
If bearings are to be mounted directly onto the shaft, the cylindricity tolerance and total runout tolerance of the bearing seat should, depending on the requirements, be one to two IT tolerance grades better than the prescribed dimensional tolerance. Abutments for bearing rings should have a perpendicularity tolerance and total axial runout tolerance that is at least one IT tolerance grade better than the diameter tolerance of the associated cylindrical seat.

Shaft seal seat or counterface

Recommendations are provided in the relevant product section. Generally, seal counterfaces should be machined to tolerance class h9 or better and the cylindricity should be to tolerance grade IT5.

Shaft surface roughness

At the sleeve and seal positions, the shaft surface should have a surface roughness Ra ≤ 3,2 μm (125 μin.). Recommendations for the surface roughness of cylindrical bearing seats are provided under Bearings, units and housings and in the SKF catalogue Rolling bearings.

Housing support surface

To maximize bearing service life and prevent deformation of the housing bore, SKF recommends that the flatness of the housing support surface is to tolerance grade IT7 in accordance with ISO 1101:2012. The surface should be finished to a surface roughness Ra ≤ 12,5 μm (500 μin.).
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