A gear transmission stage has two intermeshing gears hardened by heat treatment. In order to improve the noise behavior, one of the two gears has a final form determined by hard fine machining and the other gear has a form which is determined by heat treatment and is close to finished contours.

A medical or dental handpiece has a grip. The grip includes first to third rotation shafts. The first and second shafts are connected through a first gear mechanism and the second and third shafts are connected through a second gear mechanism so that a rotation is transmitted from the first shaft through the first gear mechanism to the second shaft and then from the second shaft through the second gear mechanism to the third shaft. The first or second gear mechanism has an internal gear secured on one shaft and an external gear secured on the other shaft, the internal and the external gears being engaged with each other. The external gear is substantially enclosed within a cylindrical plane extending along a peripheral edge of the internal gear.

A driving apparatus includes a driving input gear with first gear teeth, a columnar shaft, and a driven gear that engages the driving input gear. The driven gear includes a cylindrical boss portion, a cylindrical rim portion, a web, and second gear teeth. The second gear teeth are formed at an outer peripheral surface of the rim portion. The first gear teeth are first helical teeth twisted in a first direction with respect to a direction that the rotary drive shaft extends. The second gear teeth are second helical teeth twisting in a second direction that is the opposite of the first direction. The rim portion is tapered, radially decreasing toward the end to which the web is linked. The through-hole of boss portion has an inner diameter larger than an outer diameter of the shaft.

A quiet-running, multi-layer gear assembly includes a compliant center member sandwiched between a pair of stiff outer members. The compliant center member has an outer peripheral surface with gear teeth. Each of the outer members has an outer peripheral surface with gear teeth disposed in a respective directed axial thrust pattern. The center and outer members are joined on a central hub with their outer peripheral surfaces aligned so as to form a gear assembly with low or no net axial thrust. In some aspects, the compliant center member and the hub include cooperating anti-turn constructions.

A gear transmission device includes a drive rotator and a driven external gear. The drive rotator includes a drive internal gear to rotate about a rotary shaft. The driven external gear meshes with the drive internal gear to transmit a drive force to a drive target.

A medical or dental handpiece has a grip. The grip includes first to third rotation shafts. The first and second shafts are connected through a first gear mechanism and the second and third shafts are connected through a second gear mechanism so that a rotation is transmitted from the first shaft through the first gear mechanism to the second shaft and then from the second shaft through the second gear mechanism to the third shaft. The first or second gear mechanism has an internal gear secured on one shaft and an external gear secured on the other shaft, the internal and the external gears being engaged with each other. The external gear is substantially enclosed within a cylindrical plane extending along a peripheral edge of the internal gear.