Power transmission mechanism with automatic clutch means

Claim 1

A power transmission mechanism comprising: a first rotary member having a boring bore through the axis thereof, a polygonal flange raising from the inner wall surface thereof at one end, a toothed portion raising around the inner wall surface thereof adjacent to said polygonal flange and disposed in longitudinal direction, and an annular groove around the outer wall surface thereof at an opposite end; a socket mounted on said first rotary member over said polygonal flange; a first spring retained in said socket between said first rotary member; a revolving shaft inserted through said first rotary member and connected to a power unit, said first spring and said socket, said revolving shaft having an expanded head portion at one end set inside said first rotary member and stopped against said polygonal flange, a groove around the outer wall surface thereof and retained by a snap retainer outside said socket; a second rotary member having a boring bore through the axis thereof, a toothed portion at one end around the periphery thereof releasably engaged with the toothed portion on said first rotary member, and a circular projection at an opposite end, said circular projection defining therein a polygonal hole for fastening a tool retained in place by a retainer ring; a cap having a flange at one end engaged in said annular groove on said first rotary member and a through-hole through the axis thereof for the passing therethrough of said tool; a second spring mounted on said circular projection and retained between said cap; wherein rotating said revolving shaft causes said first rotary member to drive said tool to rotate via said second rotary member; and wherein said cap and said first rotary member are forced to move backwards toward said socket, when the resisting force which acts onto said tool surpasses the driving force from said revolving shaft, causing said second rotary member to disconnect from said first rotary member and said revolving shaft.