METHOD FOR MEASURING DEVIATION OF CONNECTING POSITION OF MEMBER, METHOD FOR PRODUCING SPARK PLUG

摘要

A measurement surface (360) is observed while a main fitting (50) is screw-engaged in a female thread holder (300), to measure the deviation of a ground electrode (30) from an optimum ignition position. The axis (O) of the main fitting (50), and a first measurement point (P1) and a second measurement point (P2), which are predetermined on a front end surface (30a) of the ground electrode (30) are detected to measure a circumferential angle (ß1) between a reference straight line (LS) connecting the axis (O) of the main fitting (50) to the optimum ignition position (O1) and a first straight line (L1) connecting the axis (O) to the first measure point (P1), and a circumferential angle (ß2) between the reference straight line (LS) and a second straight line (L2) connecting the axis (O) to the second measurement point (P2). Thus, the deviation of the ground electrode (30) from the optimum ignition position (O1) is measured. The deviation is designated by a circumferential angle (a) between the reference line (LS) and a third straight line (L3) connecting the axis (O) to the center (C) of the front end surface of the ground electrode (30).