Squares are used for testing right angles, bevels for testing angles of various sizes.

V Squares And Bevels 27Fig. 26. Caliper Compasses. &.

Fig. 26. Caliper Compasses. &.

The Square consists of a short thick piece called the stock, with a longer, thinner piece at one end, and at right angles to it, called the blade. The stock projects beyond the sides of the blade, and the tool can be easily applied to the straight edge of a piece of wood, that lines may be drawn on the surface at right angles to this straight edge. All the angles of the square, exterior as well as interior, must be perfect right angles. This is not only essential for the operation just described, but also because the square is used for testing solid angles, e.g., the edge of a plank, a corner, etc.

Every good collection of tools should include several squares of different sizes, e.g., with blades 6, 8, 12, and 18 inches long.

Wooden squares.

Fig. 27. Wooden Square. 1/6.

Fig. 27. Wooden Square. 1/6.

The square should be made of hard well-seasoned wood, warranted not to warp. To give greater durability the blade is often made of steel, and the wood of the stock faced with brass on the inner side (Fig. 28). Still stronger and more trustworthy squares are made with steel blades and cast-iron stocks. Squares of this kind are particularly useful as testing squares, and one ought to be included in every good collection of tools.

To test a square. The blade is laid on the plane surface of a block of prepared wood, with the stock against a perfectly straight edge. Lines, drawn against each side of the blade, are then made on the wood. The square is next reversed, the stock is placed as before, and the edges of the blade are placed close to the lines previously made. Lines are then drawn once more along the edges of the blade. If these lines coincide, or are perfectly-parallel with those made first, the square is correct

Steel squares.

Fig. 28. Square with steel blade. 1/6.

Fig. 28. Square with steel blade. 1/6.

Fig. 29. Set bevel or mitre bevel. 1.

Fig. 29. Set-bevel or mitre-bevel. 1.

2. The set-bevel (Fig. 29) consists, like the preceding, of a stock and a blade, but the latter, which generally extends beyond the end of the stock, is attached in such a way that it forms on one side an angle of 45°, and on the other an angle of 135°, or the complementary angle of a straight angle. It is used when a rectangular corner is made by joining together pieces cut at an angle of 45°. Such pieces are said to be mitred.

In the wooden bevel the blade rotates on a screw in the stock. To secure the blade in any given position the screw is furnished with a nut, by means of which it may be screwed fast. (Fig. 30.)

Fig. 30. The Wooden Bevel. 1/5.

Fig. 30. The Wooden Bevel. 1/5.

VI. Winding laths or straight edges. To test the accuracy of plane surfaces, a long, perfectly straight ruler or straight edge is used. When this is placed on the surface in various directions, there must be complete contact between it and the surface. A still more delicate method of proof is furnished by the double straight edge, or two straight edges exactly the same (Fig. 31). In applying the test the straight edges are placed one at each end of the piece of wood, and parallel to one another. On careful inspection, if the surface is level the upper edges of the rulers will be found to be in the same plane. The straight edges, when not in use, are held together by a couple of pegs.

To test a plane surface.

Fig. 31. Winding laths or straight edges. 1/8.

Fig. 31. Winding laths or straight edges. 1/8.

The edge of the trying-plane is often used instead of the straight edge, and two trying-planes instead of the double straight edge. See further under "face planing," p. 132.