A duplicating drawing apparatus comprising:
- a frame having a bottom wall, and a pair of racks extending in a X direction along opposite edges of the bottom wall, and having a pair of upright side walls each with a groove defined therein extending along the X direction;
- a support assembly mounted on said frame for substantial linear movement in the X direction, and including a pair of spaced-apart pinion gears secured on a transverse rod that is aligned along a Y direction perpendicular to the X direction, the gears being respectively meshed with and rolling in the X direction along the racks, whereby the trasverse rod is restrained in its alignment along the Y direction while the support assembly is continuously adjustable in the X direction relative to the racks;
- and the ends of the transverse rod extending in the Y direction beyond the respective gears and into the respective side-wall grooves;
- a pair of rotary members, each member being rotatably mounted on said support assembly by means of a subassembly that slides in the Y direction along the transverse rod, and each rotary member being so mounted for rotation about a respetive Z axis extending in a Z direction that is substantially at a right angle to said X and Y directions, said Z axes being substantially parallel to one another;
- means for introducing substantial frictional drag in motion of the subassembly relative to the transverse rod;
- connecting means attached to each of said rotary members for causing one rotary member to rotate in a substantially equal and opposite direction when the other rotary member is rotated;
- an extension arm attached to each of said rotary members;
- and
- means attached to each of said extension arms for holding a writing instrument;
- said drag-introducing means substantially preventing motion of the subassembly along or about the transverse rod during manipulation of the extension arms;
- and
- said extension arms being raisable from said frame by rotation of the subassembly about an axis defined by the transverse rod, through rolling motion of the pinions along the racks, despite said prevention of subassembly motion about the transverse rod by said drag-introducing means, and despite retention of the subassembly in place on the frame by restraint of the transverse-rod arm ends in said grooves;
- whereby said pinions, racks, grooves and transverse-rod arm ends cooperate to permit rotary raising of said extension arms without subassembly motion relative to the transverse rod, while the subassembly is retained on the frame.