Tracing device

Claim 1

In a tracing device comprising: a fluid tight box having a transparent glass top plate, a bottom, having integral upwardly extending bosses for holding the lower ends of shafts for pulleys, side walls having an inwardly extending flange for supporting said top plate, a frame around said side walls, anchored and sealed to said bottom and covering the outer edges of said top plate, powder in said box which can cover the inside surface of said top plate to make it opaque, a stylus movable in said box for scraping the powder from said surface to form a line, pulley means journalled in said box for strings for moving said stylus, and manual means projecting outside said box through said frame for operating said pulley means, the improvement in said side walls of said box comprising: integral inwardly extending bosses for holding the upper ends of the shafts for said pulleys, grooves in said flange adjacent the edges of said top plate for a nonhardening adhesive to seal said top plate to said side walls to prevent the escape of said powder, apertures in said flange having recesses for washers through which said manual means project outside said box, and said manual means having hub-portions for holding said washers in said recesses to prevent leakage of said powder from said box, and a further improvement in said device including a transparent plastic safety sheet covering said top plate having its edges under said frame and being held in place by a portion of the manual means that projects outside said box, said sheet retaining any parts of said glass top within said box in case said glass plate is broken.