Knock-out type mechanical pencil with retractable eraser

A knock-out type mechanical pencil comprising:

• a tubular cylindrical body (1) invertable between a writing position and an erasing position, said body having a first end oriented downwardly when the pencil is in the writing position and a second, opposite end;
• a cylindrical knock-button member (2) axially slidably inserted into said second end of said cylindrical body for feeding writing lead to said first end, said cylindrical knock-button member having an axial hole (4);
• a supporting rod (8) inside said knock-button member (2) and having first and second ends (12, 9) oriented the same as said first and second ends of said body, said supporting rod (8) being axially slidably movable in said cylindrical knock-button member (2) by the inversion of said body (1);
• an eraser (11) mounted on the second end (9) of said supporting rod (8) and extendable from within said knock-button member (2) through said axial hole (4) by movement of said rod (8) when said body (1) is inverted to the erasing position;
• a tubular cylindrical weight (16) surrounding said supporting rod (8) and slidable therealong towards said first and second ends by the inversion of said body;
• an annular, inwardly extending guide portion (15) formed on the interior of said cylindrical knock-button member (2) and surrounding said rod, said guide portion (15) being so located on said knock-button member (2) as to coact with said weight (16) when the latter is adjacent the first end (12) of said rod (8) for causing the rod (8) to be generally on the axis of said knock-button member (2), said weight (16) being free of said guide portion (15) when adjacent the second end (9) of said rod (8) to allow said first end (12) of said rod to assume a non-axial condition with respect to said cylindrical knock-button member (2);
• a tubular cylindrical element (13) fixedly disposed within said knock-button member (2), said element (13) surrounding said rod (8) when said body is in the writing position, said first end (12) of said rod (8) engaging said element (13) when said rod (8) is in the non-axial condition for preventing movement of said rod towards said first end of said body;
• said pencil having a cylindrical holder (10) for said eraser (11) mounted on said second end (9) of said supporting rod (8) within said knock-button member (2) and slidably contacting the interior surface of said knock-button member (2), said holder (10) and knock-button member interior surface being formed to prevent said holder (10) from turning with respect to said knock-button member (2);
• and
• an additional cylindrical weight (17) surrounding said supporting rod (8) and positioned above said tubular weight (16) when said body is in said writing position, said additional weight (17) having an outer diameter slightly larger than the inner diameter of said inwardly extending guide portion (15).