Abstract

An electrical screwdriver capable of powering off automatically when a screw is tightened which may be operated either by a manually controlled switch or by a contact-artuation switch while the twisting force required in tightening a screw may be adjusted. When the screwdriver is pushed forward, a main shaft thereof will receive a resistance and pushes a wound end of a steel wire passing through each parts thereof and causes the other end of the wire to touch a first contact switch controlling a motor contained in the handle of the screwdriver, and thereby causes the main shaft to rotate. When the screw is tightened, the rotation head of the screwdriver will push the clutch forward and causes two spring plates in the handle to recover their downward inclined position and separate from a second contact switch controlling the supply of power. An adjusting sleeve and two adjusting screws may be used to set the screwdriver to a manually controlled operation mode by fixing the adjusting sleeve to a position near the back side. A rotation collar and a slidable member with scales indicating torsion value, together with a compression spring between them may control and decide the twisting force required in tightening a screw.