Straight edge assembly
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to drawing aids, and particularly to a straight edge assembly for use with an artist&#39;s canvas. 
     2. General Description of the Prior Art 
     While a great deal of art work is done on canvases mounted on solid board, particularly indoor studio work, a substantial quantity of art work is done, particularly outside, wherein a canvas is supported on a simple rectangular frame, commonly referred to as a stretcher. It is to be appreciated that in the fixed locale indoor environment, the artist&#39;s tools need not be particularly portable, and thus it has been found in general there is a greater variety of drawing aids which are more adaptable for the studio locale than for field usage. A particular case in point is the adjustably mounted straight edge which enables one to draw a series of parallel straight lines. There are a variety of such devices which may be mounted on drafting boards, but the applicant is unaware of any such device which is mountable on a stretched canvas. These devices are positioned very close to the surface of the board, and thus are unsuitable for use with an artist&#39;s brush. 
     Accordingly, it is an object of this invention to provide such a device. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, an arm or rod having a straight edge is positioned a spaced distance from the surface of a canvas by virtue of longitudinal extending slots in opposite end regions, through which a connector extends. Each connector is adjustably secured in a slot in the front side of separate slotted blocks, which blocks are oppositely positioned along outer sides of a frame, or stretcher, or a stretched canvas. In turn, each of these blocks is clamped by a connector which connects between a back side of a block to a slotted L-shaped block which adjustably clamps a side mounted block to the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of an embodiment of the invention with a portion broken away and enlarged. 
     FIG. 2 is a partial plane view, partly in section, along lines 2--2 of FIG. 1. 
     FIG. 3 is a pictorial view of one of the clamping blocks employed by the invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to FIG. 1, a stretched canvas 10 is shown supported on a conventional, partially shown, easel 12. Stretched canvas 10 consists of a rectangular frame 14 of rectangular cross sectioned frame members 16 on which there is stretched and attached (by means not shown) a sheet of canvas 18 of a type employed by artists. Straight edge 20 is supported a fixed distance from the surface of canvas 18 by a pair of identical bracket assemblies 22 and 24, assembly 22 being shown in detail. A mounting block 26 of bracket assembly 22 is L-shaped and includes perpendicular joining surfaces 28 and 30 (FIG. 3) which engage rectangularly cross sectioned frame member 16. Mounting block 26 includes a longitudinal slot 32 which extends from a point 34 near end 36 to a point 38. Additionally, there are a plurality of pin-like protrusions 40 (FIG. 3) extending from joining surface 28 of block 26 to enable a more effective frictional engagement with frame member 16. 
     Side clamping block 42, which mates with mounting block 26, has a stud 44 firmly mounted in the rear of the block, and it extends through slot 32 of block 26, and the two are attachable by means of butterfly nut 46. Thus, in assembly, blocks 26 and 42 are pressed together, with frame member 16 between them, and butterfly nut 46 tightened. Side clamping block 42 extends forward of canvas 18 to include hollow region 48 which is closed, on a front side 50, by a plate 52 having a longitudinal slot 54. A bolt 55 is positioned with its head within hollow region 48 of block 42 and with its shank region extending out through slot 54, the bolt thus being locked from complete removal by virtue of slot 54 being of smaller width than the diameter of the head of bolt 55. 
     Straight edge 20 includes longitudinally extending slots 58 and 60 in its end regions, and thus as shown, bolts 55 extend through slots 58 and 60 and are lockable by means of butterfly nut 61. 
     In use, mounting blocks 26 of bracket assemblies 22 and 24 would be positioned on frame 14 where desired and locked in place by pressing side clamping blocks 42 against the outer side of frame member 16. Then tighten butterfly nut 46, thus firmly clamping bracket assemblies 22 and 24 to frame members 16 on opposite sides of frame 14. Then, straight edge 20 would be positioned with bolts 55 extending through slots 58 and 60, and then with straight edge 56 oriented as desired, nuts 61 would be tightened on bolts 55, and thus straight edge 20 would be locked in a desired position. This enables an artist to draw a straight line along straight edge 20 on canvas 18. If it is desired to draw a parallel or near-parallel line nearby, nuts 61 would be loosened and straight edge 20 appropriately shifted and then the nuts retightened. In the event that the desired shift would exceed the limits imposed by the combination of slots 58 and 60 in straight edge 20 and slot 54 in mounting block 42, then it would be necessary to shift one or both of bracket assemblies 2 and 24 to a new position by loosening butterfly nuts 46 as required, repositioning a bracket assembly or assemblies and then retightening the butterfly nuts. 
     From the foregoing, it is to be appreciated that the applicant has determined a straight edge device which does not require mounting to a solid board and which can be readily attached, removed and repositioned on a stretched canvas.