Method and device for drawing curved lines

Abstract

A drafting tool for drawing a circle or curved arc has interlocked, independently rotatable concentric rings. The rings have radially extending openings that can be aligned to form a radial track. A carriage for carrying a pencil or other marking element is slidable along the track to a desired radial position. The carriage can occupy one or more than one of the rings and rotates with the ring(s) around a center point. The carriage has a locking structure that is spring biased to retract and advances to lock the carriage in position at the desired radius when the pencil or the like is inserted. The locking structure can have a tooth for engaging between teeth along the radial openings in the track, the teeth on the track forming part of the sliding support for the carriage. The rings have complementary tongues and grooves, and nodules on at least one of the abutting surfaces of the tongues and grooves minimizes surface contact to reduce friction. The rings, and preferably a central disk, are secured in a rectangular base having anti-skid pads.

Dependencies are inferred from the claim text.