Abstract: A laser groove machining method for forming bottomed grooves in a surface of a workpiece using a laser, wherein an emitting position of a laser beam which is to be emitted onto the workpiece is shifted relatively along groove forming positions at a high speed of 150 mm/min. or faster. Thus, melted portions which are melted by the laser beam can easily be separated, cooled and removed by shifting the laser beam emitting position at high speed. In addition, water may be jetted to the workpiece so as to form a pillar of water so that the laser beam is emitted through the interior of the pillar of water so formed.

Abstract: A laser groove machining method for forming bottomed grooves in a surface of a workpiece using a laser, wherein an emitting position of a laser beam which is to be emitted onto the workpiece is shifted relatively along groove forming positions at a high speed of 150 mm/min. or faster. Thus, melted portions which are melted by the laser beam can easily be separated, cooled and removed by shifting the laser beam emitting position at high speed. In addition, water may be jetted to the workpiece so as to form a pillar of water so that the laser beam is emitted through the interior of the pillar of water so formed.

Abstract: A laser groove machining method for forming bottomed grooves in a surface of a workpiece using a laser, wherein an emitting position of a laser beam which is to be emitted onto the workpiece is shifted relatively along groove forming positions at a high speed of 150 mm/min. or faster. Thus, melted portions which are melted by the laser beam can easily be separated, cooled and removed by shifting the laser beam emitting position at high speed. In addition, water may be jetted to the workpiece so as to form a pillar of water so that the laser beam is emitted through the interior of the pillar of water so formed.

Abstract: Disclosed is an improved switch structure having forcedly opening-and-locking mechanism installed therein. It is responsive to the sticking of the movable and stationary contact elements for forcedly breaking an associated heavy-current carrying circuit which otherwise, would remain closed through the stuck contact elements. The forcedly opening-and-locking mechanism comprises an auxiliary contact section spring-biased to retain the stationary contact element in conductive condition to the associated circuit. It is responsive to the sticking-and-rising of the movable and stationary contact elements for allowing the stationary contact element to be apart from the conductive position to the associated circuit by yielding the rising force of the stuck contact elements until the locking position is reached, in which position the stationary contact element is kept in non-conductive position.

Abstract: A road cutting machine comprises a machine body (2) mounted to a travelling body (1) to be swivel, a boom (4) mounted to the machine body to be vertically swingable, an arm (6) mounted to the boom to be swingable in a vertical direction and a road cutting apparatus (A) mounted to the arm, the road cutting apparatus includes a mounting member (20) attached to the arm, a hydraulic motor (50) mounted to the mounting member and a cutting bit mounting member (99) rotated by the hydraulic motor and having a plurality of cutting bits, the cutting bit mounting member is provided with a main cutting bit (100) mounted to a center of rotation, a plurality of flat surface cutting bits (103, 104) attached in a range from the rotation center side to an outer periphery side, a plurality of sweep-cutting bits (105) attached on the outer periphery side and a plurality of side surface cutting bits (106, 107) attached on the outer periphery side, a bit tip end portion (100a) of the main cutting bit is positioned in a lowermost