Patent attributes
A numerically controlled machine tool performs machining by rotating a rotational tool attached to a tool holder mounted on a spindle, with keys fitted into key grooves in the tool holder. The numerically controlled machine tool includes predetermined-amount rotating unit for stopping the tool holder at a predetermined rotational position and then rotating the tool holder by a given amount, and a distance sensor which is installed apart from the tool holder and measures a distance to the outer surface of the tool holder. The predetermined-amount rotating unit stops the tool holder at a rotational position at which the key grooves do not face the distance sensor, then rotates the tool holder by the given amount. The distance sensor measures the distance to the tool holder while the tool holder is rotating. The measurement result is compared with a reference distance or distances to discriminate between normal and abnormal rotational run-out of the tool holder.
