Abstract: An oil seal for sealing off a fast rotating shaft (10) relative to a housing (11) comprises a first seal element (15) mounted on the shaft (10), a second seal element (18) resiliently mounted in the housing (11), both seal elements (15, 18) having cooperating contact surfaces (25, 26), and a spring (22) acting on the second seal element (18) to provide an axial contact pressure between the contact surfaces (25, 26). The contact surfaces (25, 26) of the seal elements (15, 18) are made of materials of different hardness, and the one consisting of the hardest material is formed with one or more circular ribs (27a-c) disposed concentrically with the shaft (10) and intended to cut mating circular grooves in the other seal element contact surface (25) during a running-in period.

Abstract: A portable power grinder comprises a housing (11), a rotation motor (10) with a rotor (13) having a rear end portion (27) extending out of the motor (10), an output shaft (22) which is drivingly coupled via a reduction gearing (23) to the rotor shaft (13) and intended to carry a grinding tool, and a speed governor (18) for providing a constant motor speed. The reduction gearing (23) comprises a gear (24) integral with the rotor shaft (13) and another gear (25) integral with the output shaft (22). Alternative rotor shafts (13) with gears (24) of different sizes may replace each other for obtaining different gear ratios and different output speed levels, and the length of the rear end portion (27) of the rotor shafts (13) varies with the size of the integral gear (24). The housing (11) has a detachable lid (15) carrying the speed marking (2) of the tool and having an internal projection (28) of a size directly related to the speed level readable on the speed marking (21).