PURPOSE: To eliminate generation of burrs by molding a boundary between an internal peripheral surface and a groove into a continued shape of curved surface, and then cutting the internal peripheral surface into finish dimension, in the case of forming a sleeve provided with a plurality of streaks of the grooves in parallel to the axial center in the internal peripheral surface for guiding a piston.
CONSTITUTION: A sleeve 21, provided in a master cylinder 20, is formed in a cylindrical shape to provide a flange part 21a in a point end part external peripheral surface, and an annular protrusion 21b and an annular groove 21c are provided in a peripheral surface in the point end side from this flange part 21a. In this sleeve 21, six grooves 21e are parallelly formed to the axial center of the sleeve 21 in an internal peripheral surface 21d. Further in this sleeve 21, six holes 21f, reaching the internal peripheral surface 21d from the external peripheral surface, are provided inserted, and each hole 21f is opened to a bottom part of the groove 21e. This sleeve 21 is formed by aluminum cold forging but here molded in a condition that the groove 21e is connected to an internal peripheral surface 21d' by a curved surface of radius of curvature R2, thereafter the internal peripheral surface 21d is obtained by cutting the internal peripheral surface 21d'.
SEKIGUCHI NOBORU
SUGIMOTO RIICHIRO
