MISCELLANEOUS TOOLS AND METHODS OF WORK 48 
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. 
U UU UU UU dU 
8 AA) es oe 9 ce wi 
b 
The artist’s drawing represents ob- yy¢.56, The Difference be- 
jects as they appear, while the — tween Perspective and 
: ‘ Mechanical Drawing 
mechanical drawing represents 
them as they really are. Things 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, 
