MISCELLANEOUS TOOLS AND METHODS OF WORK 43 



head. Two methods of fastening with flat-head screws 

 are shown in Fig. 55. 



Sketch A shows the two pieces of wood in position, 

 the hole bored in upper piece (only) and countersunk ; 

 B shows the screw in position. In this case the screw 

 head is visible. It is occasionally desirable to hide the 

 screw entirely. Sketch C shows the hole prepared for 

 the screw ; D shows the screw in position and a circular 

 wooden plug driven in over it. 

 The plug is then leveled with the 

 surface and the screw completely 

 hidden. 



27. Mechanical Drawing. A me- 

 chanical, or working, drawing is 

 quite different from a pictorial 

 drawing such as an artist produces. 

 The artist's drawing represents ob- FlG>56 . The Difference be- 

 jects as they appear, while the tween Perspective and 



, . . Mechanical Drawing 



mechanical drawing represents 



them as they really are. Tilings in nature do not look 

 as they are. For example, when we stand on a railroad 

 track the rails appear to converge until they seem to 

 meet in the distance. We know that this is not the 

 case, that the rails are really everywhere equally distant. 

 The optical illusion of the rails meeting at the hori- 

 zon is called perspective. Mechanical, or constructive, 



