Importance

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Abstract

A mechanical pencil for automatic drawing machines is disclosed which feeds lead segments to the writing surface as the pencil is alternately pressed against and lifted from the writing surface. The pencil includes a housing having a reserve lead containment chamber and a main internal cavity. A collet split into two portions is mounted within the internal cavity beneath an opening between the main cavity and the containment chamber and has outer cone-shaped camming surfaces and first and second axially spaced, cylindrical inner clamping surfaces. A friction tube with an inner bore adapted to frictionally engage a lead segment is mounted beneath the collet and holds a lead segment to support it against the writing surface. When the tip of the friction tube is pressed against a writing surface, the friction tube pushes upwardly on a return spring which in turn drives a collet closing bushing against the bottom surface of the collet portions, driving the outer conical camming surfaces of the collet into contact with an abutment shoulder within the cavity to drive the collet portions together such that the first and second clamping surfaces engage and hold the lead segment. When the pencil is lifted from the writing surface, the pressure on the collet is released and the collet portions separate to allow the lead segment therein to be drawn downwardly by the friction tube.

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First Claim