Fig. 46
Fig. 47
Fig. 48
Figs. 39 to 48.—Carving Air-screws.
The block may now be prepared from these dimensions. American whitewood, silver spruce, mahogany, or walnut are the most suitable woods to use. The block should be planed up true and square, and a hole drilled axially through its geometrical centre. The first operation is to rough the block out to the shape shown by [Fig. 39], which shows the Chauvière type. Of course, other shapes may be used as desired, but the method of manufacture is the same. Now, with a flat chisel or woodworker’s knife pare the wood away ([see Fig. 40]) until the hollow or concave side of the blade is formed ([see Fig. 41]). The obverse side of the other blade is then similarly treated ([see Fig. 42]), which clearly shows how the blade is hollowed out.
[Fig. 43] shows the method of forming the boss of the screw, and [Fig. 44] how the reverse or convex side of the blade is shaped. [Fig. 45] shows the screw roughed out, and [Fig. 46] indicates the glass-papering operation.
At this stage the screw has to be balanced. This is of great importance, since the screw that is unbalanced loses a great amount of efficiency owing to the consequent vibration when it rotates. In full-size practice it would be highly dangerous to use a screw that is not balanced.