Drafting machine attachment

An attachment for a drafting machine mountable on a drawing board and having a protactor head fitted with a chuck, said attachment comprising a scale having an end member connectable to the chuck, said scale being operable by the protractor head to extend across the drawing board located in a first position and in a second position disposed at a predetermined acute angle to said first position, a ruling edge on the scale, an extension on the scale near an end remote from the end member, said extension having parallel side edges providing ruling edges perpendicular to the ruling edge on the scale, said ruling edges of the extension combining with the ruling edge of the scale to form a first index point and a second index point spaced therefrom, said first and second index points being usable to mark the locations of required symbols, a template having a plurality of symbol outlines, mounting means supporting the template on the scale for rotation about an axis perpendicular to the drawing board, said mounting means including a shaft having a lower end, coupling means detachably securing the template to the lower end of the shaft, said symbol outlines being arranged on the template in concentric rows having a radial spacing equal to the spacing between the first and second index points, said symbol outlines additionally being arranged in radial rows uniformly spaced apart, an indicator on the mounting means for locating a required symbol outline in a position to coincide with a marked location when the scale is moved to the second position, and an indexing device including a first member rotatable with the template and a second member non-rotatably supported by the mounting means, said first and second members co-operating to progressively bring the radial rows of symbol outlines into register with the indicator.