1. A method of manufacturing an index device of a machine tool, the method comprising:
providing a jig having an outer periphery of the same outer diameter as an outer diameter of a motor for driving the index
prior to setting the motor into a casing configured to house the motor, inserting the jig into the casing;
filling, through an opening provided in the casing, a material with higher thermal conductivity than the air into a gap space
created between the casing and the outer periphery of the jig;
removing the jig from the casing when the material filled in the gap space becomes solidified; and
setting the motor into the casing after said removing the jig from the casing.