The optimal surface finish for the bore largely depends on the type of shaft seal in use. Generally speaking, seals with a rubber-covered O.D. can handle a rougher surface finish than metal O.D. seals, but a surface that’s too rough may damage the O.D. or prevent formation of a tight static seal. On the other hand, a surface that’s too smooth may make it more difficult for a seal with a rubber-covered O.D. to stay in place. While there is no accepted standard for minimum bore roughness, we recommend a roughness of at least 2.03 µm (80 µin) Ra. If the bore exceeds 2.54 µm (100 µin) Ra, then a rubber O.D. seal or use of O.D. sealant is recommended. Bore roughness should never exceed 3.175 µm (125 µin) Ra.

“Good design doesn’t stop with the shaft seal and the shaft. Due consideration must also be given to the housing bore.”