A method of manufacturing a hydrostatic gas bearing comprising the steps of:
- (a) preparing a synthetic resin-made bearing base having a base portion, an annular protruding portion provided integrally on and protruding from one surface of the base portion, and an air supply passage which is provided in the annular protruding portion and the base portion and which has one end open at a protruding end face of the annular protruding portion and another end open at an outer peripheral surface of the base portion, wherein an outer peripheral surface of the annular protruding portion has a cylindrical outer wall surface, an annular truncated conical outer wall surface which is gradually enlarged in diameter outwardly from the cylindrical outer wall surface in such a manner as to continue from the cylindrical outer wall surface, and a cylindrical outer wall surface larger in diameter than the cylindrical outer wall surface and continuous from the one surface of the base portion in such a manner as to continue from the truncated conical outer wall surface, while an inner peripheral surface of the annular protruding portion has a cylindrical inner wall surface, an annular truncated conical inner wall surface which is gradually reduced in diameter inwardly from the cylindrical inner wall surface in such a manner as to continue from the cylindrical inner wall surface, and a cylindrical inner wall surface smaller in diameter than the cylindrical inner wall surface and continuous from the one surface of the base portion in such a manner as to continue from the truncated conical inner wall surface;
- (b) preparing a synthetic resin-made bearing body having an annular recessed portion which is formed in one surface of the bearing body, an annular recessed groove which is open at another surface of the bearing body, and a plurality of air outlet holes each of which communicates with the annular recessed groove at one end thereof and opens to the annular recessed portion at another end thereof, wherein an outer-side inner peripheral surface defining the annular recessed portion includes an outer cylindrical inner wall surface having an annular peripheral edge defining an outer edge of an open end of the annular recessed portion, while an inner-side inner peripheral surface defining the annular recessed portion has an inner cylindrical inner wall surface having an annular peripheral edge defining an inner edge of the open end of the annular recessed portion;
- (c) causing the one surface of said bearing body to oppose the one surface of the base portion, causing the annular recessed portion of said bearing body to receive the annular protruding portion of said bearing base, and causing the annular peripheral edge of the outer cylindrical inner wall surface defining the outer edge of the open end of the annular recessed portion and the annular peripheral edge of the inner cylindrical inner wall surface defining the inner edge of the open end of the annular recessed portion to be respectively brought into contact with the truncated conical outer wall surface of the outer peripheral surface of the annular protruding portion and the truncated conical inner wall surface of the inner peripheral surface of the annular protruding portion, so as to form an assembly of said bearing body and said bearing base;
- (d) welding and joining said bearing body to said bearing base at portions of the contact by pressing a tool horn against said bearing body in the assembly and by imparting ultrasonic vibrations thereto under welding conditions of a welding pressure of 0.098 to 0.60 MPa, a vibrational amplitude of 20 to 80 μm, an emitting time of 0.1 to 1.5 seconds, and a hold time of 0.5 to 1.0 second;
- and
- (e) irradiating the other surface of said bearing body welded and joined to said bearing base with a laser beam to thereby form the annular recessed groove with a width of at least 0.3 mm and a depth of at least 0.01 mm and the plurality of air outlet holes serving as inherent restrictors each of which communicates with the annular recessed groove at the one end thereof, opens to the annular recessed portion at the another end thereof, and has a diameter of at least 30 μm at the one end.