MISCELLANEOUS TOOLS AND METHODS OF WOKK 43 



head. Two methods of fastening with flat-head screws 

 are shown in Fig. 55. 



Sketch A sliows tlie two pieces of wood in position, 

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

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

 head is visible. It is occasionally desirable to hide the 

 screw entirely. Sketch shows the hole prepared for 

 the screw ; I> shows the screw in position and a circular 

 wooden plug driven iir 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- 

 jects as they appear, while the 

 m echanical d raw in g r e p r e s e n t s 

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

 as they are. For example, wlien 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 tlie 

 case, that the rails are real!}' evervwhere equally distant. 

 The optical illusion of the rails meeting at the hori- 

 zon is called perspective. Mechanical, or constructive. 





Fig. .56. The Difierence be- 

 tween Perspective and 

 Mechanical Drawing 



