Patent ID: 7766787

Claim:
A hand-held rotating power tool comprising a body being hollow and having an open front end and an inner cavity; a power unit being mounted inside the inner cavity and having an armature being mounted rotatably in and protruding from the power unit; and a transmission assembly having a transmission casing being hollow and cylindrical, being detachably mounted coaxially on and protruding from the open front end of the body and having a through hole; a common annulus being tubular, being mounted securely in the transmission casing adjacent to the open front end of the body and having an inner surface; and multiple teeth being formed longitudinally around the inner surface; at least two planetary gear assemblies being mounted in series and comprising a first stage planetary gear assembly being connected to and rotated by the armature and a final stage planetary gear assembly, and each planetary gear assembly having a rotational axis and comprising a sun gear being mounted coaxially on the rotational axis, wherein the sun gear of the first stage planetary gear is connected to and protrudes coaxially from the spindle of the armature and the sun gear of the final stage planetary gear assembly is rotated by the armature; a planet carrier being an annular bracket, being mounted rotatably around the sun gear and having a front surface, a rear surface, an outer edge, a central hole being formed concentrically in the rear surface and being mounted around the sun gear, and a front bearing mount being formed coaxially on and protruding from the front surface; at least three gear recesses being evenly formed radially in the outer edge and communicating with the central hole, and each gear recess having two pinholes being formed respectively through the front and rear surfaces of the planet carrier and being aligned with each other and a pivot pin being mounted longitudinally in the aligned pinholes, wherein at least one of the planet carriers further has a mounting recess formed concentrically in the rear surface near the outer edge; and the planet carrier of the first stage planetary gear assembly further has a rear bearing mount; and at least three planetary gears being mounted rotatably respectively around the pivot pins respectively in the gear recesses and engaging the sun gear in the central hole and the teeth of the common annulus; a thrust washer assembly being mounted between the first stage planetary gear assembly and an adjacent planetary gear assembly around the sun gear of the adjacent planetary gear assembly and in the mounting recess in the planet carrier of the adjacent planetary gear assembly and having a resilient washer absorbing movement in an axial direction and having two sides; and at least one flat washer being mounted respectively on at least one of the sides of the resilient washer; and a bearing assembly being mounted on the planet carrier and having a bearing being mounted securely in the common annulus and on the front bearing mount of the planet carrier.