Abstract: A method of manufacturing a metal shell assembly for a spark plug including a cylindrical metal shell that extends in a direction of a central axis and which has a screw portion formed in an outer peripheral surface thereof, and a bar-shaped ground electrode that extends from a front end portion of the metal shell, the method including: disposing an intermediate assembly, having the ground electrode provided in a metal shell intermediate body, between a plurality of rolling dies having process surfaces facing each other; forming the screw portion by performing a rolling process on the intermediate assembly by the plurality of rolling dies while the intermediate assembly is interposed between the plurality of rolling dies; and positioning the ground electrode in a circumferential direction about a central axis of the intermediate assembly between the disposing and forming steps.

Abstract: A method for measuring a deviation from a joint target position of a member to which a measuring object is joined, in particular, measuring the deviation of an electrode position of a spark plug. The deviation of a ground electrode from an optimal igniting position O1 is measured while a metallic shell is engaged with a female thread jig. A distance “?” between an axis A of the ground electrode and a reference straight line LS is calculated. The distance “?” is a vertical length from the axis A to the reference straight line LS. An angle “?” between a first straight line L1 and the reference straight line LS is calculated using the distance “?” and a predetermined distance “?” between the axis A of the ground electrode and an axis O of the metallic shell.

Abstract: In a method for measuring deviation of a ground electrode from an optimal igniting position, a metallic shell is engaged with a female thread jig. Then the axis O of the metallic shell, a predetermined first measuring point P1 and a predetermined second measuring point P2 on a front end face of the ground electrode are detected. Then, a circumferential angle ?1 formed between a reference straight line “LS” connecting O to the optimal igniting position O1, and a first straight line L1 which connects O to P1 is measured, followed by a measurement of a circumferential angle ?2 formed between LS and a second straight line L2 connecting O to P2 Thereafter, the deviation of the ground electrode from O1 is measured as a circumferential angle “?” between “LS” and a third straight line L3 connecting the axis O to the center C of the front end face.

Abstract: A method for measuring a deviation from a joint target position of a member to which a measuring object is joined, in particular, measuring the deviation of an electrode position of a spark plug. The deviation of a ground electrode from an optimal igniting position O1 is measured while a metallic shell is engaged with a female thread jig. A distance “?” between an axis A of the ground electrode and a reference straight line LS is calculated. The distance “?” is a vertical length from the axis A to the reference straight line LS. An angle “?” between a first straight line L1 and the reference straight line LS is calculated using the distance “?” and a predetermined distance “?” between the axis A of the ground electrode and an axis O of the metallic shell.

Abstract: In a method for measuring deviation of a ground electrode from an optimal igniting position, a metallic shell is engaged with a female thread jig. Then the axis O of the metallic shell, a predetermined first measuring point P1 and a predetermined second measuring point P2 on a front end face of the ground electrode are detected. Then, a circumferential angle ?1 formed between a reference straight line “LS” connecting O to the optimal igniting position O1, and a first straight line L1 which connects O to P1 is measured, followed by a measurement of a circumferential angle ?2 formed between LS and a second straight line L2 connecting O to P2 Thereafter, the deviation of the ground electrode from O1 is measured as a circumferential angle “?” between “LS” and a third straight line L3 connecting the axis O to the center C of the front end face.

Abstract: A method of manufacturing a metal shell assembly for a spark plug including a cylindrical metal shell that extends in a direction of a central axis and which has a screw portion formed in an outer peripheral surface thereof, and a bar-shaped ground electrode that extends from a front end portion of the metal shell, the method including: disposing an intermediate assembly, having the ground electrode provided in a metal shell intermediate body, between a plurality of rolling dies having process surfaces facing each other; forming the screw portion by performing a rolling process on the intermediate assembly by the plurality of rolling dies while the intermediate assembly is interposed between the plurality of rolling dies; and positioning the ground electrode in a circumferential direction about a central axis of the intermediate assembly between the disposing and forming steps.