| 摘要 |
PURPOSE:To make the tip of a drill side-step before it is brought into contact with the holded bottom face and prevent the tip of the drill from breaking in such a way that moving speed of a main shaft cylinder is changed over to proceed cutting feed a little distance in front of the previous machined position. CONSTITUTION:During cutting, a main shaft cylinder 3 is once returned by step fee controlling means (21, 22, 23, etc.), when this returning is done, uniform coupling is done by a sliding body 55, a cylindrical body 51 and a piston rod 32 through balls 54 of a unidirectional clutch 57, the sliding body 55 and the cylindrical body 51 are moved backward as much as just for the distance L, and an angaging strip 42 to be engaged with the piston rod 32 when returning is also moved backward as much as just for the distance L. Then, when the main shaft cylinder 3 is moved forward, engaging position of a contactor 11 and the engaging strip 42 is put backward as much as just for the distance L, transfer to the cutting feed speed after this engagement is performed a little in fron of the spot nearer as much as the distance L than that of the bottom face of the hole which has been previously formed, so that the drill 1 can side-step at the fast forward speed before it is brought into contact with the work W. |
