Drafting instrument

In a drafting instrument, the combination comprising a plate for positioning on one face of a worksheet and having a circular through opening having a countersink and having calibrated scales concentrically arrayed thereabout, a dish insertable in said circular through opening and rotable therein and having upstanding along its periphery a circular wall having a frustoconical flange, said plate and said dish having a connection means mutually interfitting for connectively combining said plate and said dish, the bottom of said dish being slightly above the bottom of said plate and thus being above said worksheet, a track having a handle at each end and comprising two parallel walls integral with and upstanding from the floor of said dish, a carriage for selective slidable movement along said track and having a locking means for selectively positioning said carriage along said track, a depressible plunger having a resilient means comprising a coil compression spring and carried by said carriage and extending through a through slot of said track, a drawing lead held by said depressible plunger and depending therefrom for selective drawing engagement with said worksheet, wherein the improvement comprises said connection means comprising a semicircular groove circuiting said circular wall and at least two equally spaced resilient members defined by through slots in said wall of said dish and each having a semicircular groove and a bead and comprising at least two equally spaced nubs on said wall of said circular through opening, said track and said through slot thereof traversing the diameter of said dish to allow said carriage a range of movement for said drawing lead to draw a straight line from one point on the perimeter of said dish to an opposite point on the perimeter of said dish, said track having a handle at each end for the manipulative rotation of said dish, said carriage having angled bottom sides for receptive conformability into said track having a valley of generally V-shaped cross-sectional outline defined by inner angled sides against which said angled bottom sides receptively conform for a positive seating of said carriage to ensure a positively smooth slidable movement of said carriage therein and to prevent said carriage of any vagrant movement therein regardless of any degree of wear experienced by said angled bottom sides and said valley, said carriage having a locking means for selectively positioning said carriage along said track while at the same time depressing said depressible plunger to bring said drawing lead into bearing engagement with said worksheet, said carriage having a centering means comprising two index lines at right angles for positioning center of said dish on a reference point of said worksheet, said depressible plunger having a feeding means for said drawing lead.