Abstract: A tool holder includes a holder body having a trunk and a grip tube, a pressure ring fitted around the grip tube, a nut for axially moving the pressure ring, and a sleeve defining a pressure chamber around the outer periphery thereof. The trunk is formed with cylinders in which pistons are inserted respectively. The cylinders communicate with the pressure chamber through a communication channel. Hydraulic fluid is sealed in the cylinders, the communication channel and the pressure chamber. When the nut is rotated, the pressure ring is axially moved, thus radially compressing the grip tube. Simultaneously, the pistons are pushed into the respective cylinders, thus increasing the pressure in the pressure chamber. As a result, both a first holding hole formed in the grip and a second holding hole formed in the sleeve decrease in diameter, so that a tool inserted in these holes are held in position.

Abstract: A tool holder has a shank, a flange and a tool holding portion. From its front to rear end, the shank has on its outer periphery a first cylindrical surface, a tapered surface, and a second cylindrical surface. A tapered sleeve is mounted on the shank. Belleville springs are mounted between the large-diameter end of the tapered sleeve and the flange of the tool holder. The tapered sleeve is formed with a tapered outer surface adapted to be brought into close contact with a tapered inner surface of a bore formed in the spindle, and a cylindrical inner surface adapted to be brought into close contact with the second cylindrical surface of the shank. If a gap forms between the spindle and the tapered sleeve when the spindle is rotating at a high speed, the tapered sleeve is urged by the belleville springs in such a direction that the gap disappears, thereby maintaining a centripetal tendency and rigidity.

Abstract: A traction drive tool adapter, has a rotary portion provided at its front half section with planetary roller-inserting bores extending radially from the outer circumferential surface of the rotary portion into a central bore therein, each of the roller-inserting bores having planetary rollers driving shaft member-setting grooves continuing from two ends of the roller-inserting bore that are opposed to each other in the axial direction of the central bore.

Abstract: A traction drive spindle device includes an input shaft connectable to a drive main shaft for rotation therewith. A hollow holder shaft is connected to an output end of the input shaft in coaxial relation thereto, the hollow holder shaft having a plurality of planetary rollers mounted thereon intermediate opposite ends of the holder shaft. A high-speed spindle is rotatably received in a bore of the hollow holder shaft, the high-speed spindle having an inner end portion which is received in the bore and serves as a sun shaft disposed in rolling contact with the planetary rollers. A housing is mounted on the outer periphery of the holder shaft through a first ball-and-roller bearing so as to be rotatable relative to the holder shaft, the housing having a fixed ring fixed to an inner periphery thereof. The planetary rollers are disposed in rolling contact with the fixed ring. A second ball-and-roller bearing is interposed between the holder shaft and the high-speed spindle.

Abstract: When a drill is overloaded, while cutting a hole in a workpiece, a torque limiter disconnects the drill from a main spindle. As the drill is disconnected from the main spindle, the torque limiter generates high-level elastic waves. The elastic waves are converted by a transducer into a voltage signal. The level of the voltage signal is compared with a threshold value.