MACHINE TOOL

PROBLEM TO BE SOLVED: To make it possible to easily detect poor holding of a main shaft without provision of any special sensor and so on.SOLUTION: A machine tool (1) in which two main shafts (2, 3), which comprise opening/closing possible chucks (9, 11) and are relatively movable, are so provided as to be capable of freely hanged between a free rotation state and a rotation drive state, and rotation detection means (7, 8) which detect rotation of the main shafts (2, 3) and gripping change means which changes a gripping position of a bar stock (33) by the main shafts (2, 3) by closing the chuck at a prescribed movement position are provided, and which performs processing of the bar stock (33) while sequentially delivering the bar stock. In the machine tool, gripping failure detection means, which changes the main shaft (2) of which a gripping position is changed by the gripping change means into the free rotation state, rotationally drives the other main shaft (3), and detects gripping failure of the main shafts (2, 3) when changing the gripping position on the basis of a rotation state of the main shaft (2) in the free rotation state detected by the rotation detection means (7, 8), is provided.SELECTED DRAWING: Figure 7 【課題】特別なセンサ等を設けることなく主軸の際の把持不良を簡単に検出すること。【解決手段】開閉可能なチャック（９，１１）を備えた相対的に移動自在な２つの主軸（２，３）が自由回転状態と回転駆動状態に切り換え自在に設けられ、主軸（２，３）の回転を検出する回転検出手段（７，８）と、所定の移動位置でチャックを閉作動させることによって、主軸に（２，３）よる棒材（３３）の把持位置を変更する把持変更手段とを設け、把持変更手段によって、棒材（３３）を順次送りながら加工を行う工作機械（１）において、把持変更手段によって把持位置が変更された主軸（２）を自由回転状態に切り換えるとともに、他方の主軸（３）を回転駆動し、回転検出手段（７，８）によって検出される自由回転状態の主軸（２）の回転状態に基づいて把持位置の変更の際の主軸（２，３）の把持不良を検出する把持不良検出手段を設けた。【選択図】図７