ABC of the Steel Square and Its Uses

by Fred. T. Hodgson

Fig. 79.

When rails are cut by bandsaw on bed blocks, bevels are not necessary, as they can always be obtained by applying a bevel as shown at [Fig. 80]. The stock should lie solid on the block and square off the sides. When the block is thin it is best to apply the bevel near the corner, when a greater surface is obtained. These bevels are applied after the joint is squared off the tangent lines. To demonstrate a rail with unequal pitches, cut another piece of stuff 2x2 inches, as shown in [Fig. 79], repeat the process with the cardboard as before. It will be found that the horizontal trace has departed from the angle of 45 degrees (see [Fig. 79]) and has approached nearer one corner and gone farther away on the other. The major axis B will have done likewise, as it is always square off the horizontal trace C. The wreath having two pitches, the face mold will obviously be wider at one end than at the other; and if bevels are required, they must be set off on the face of each side of the block. The width of the face mold is to be applied on the tangent line; this makes it slightly in excess on the joint, but it is better to have a little margin in thickness for working. Where thickness of stuff is a secondary consideration, it is preferable to take the rail out of stuff which is as thick as the diameter of a circle that will enclose the section of rail; the corners will then be left complete.

Fig. 80.

Fig. 81.

The following method shows the least thickness the rail can be cut out of, and also gives width of face molds on the joint. Set the bevel to the bed block as shown at [Fig. 80], and apply at the side of the block. Draw a section of rail level; apply the bevel again, touching the bottom corner of the section. The distance between the marks is the thickness, a plumb line marked on shows the width of the face mold on the bevel line. Where the pitches are different the foregoing method has to be applied to each side of the bed block.

The bevels may be also obtained by the steel square. Take the width of prism face (shown by dotted lines) by laying the square with blade on the line C D ([Fig. 82]) and tongue, cutting at the center A. Note the length on the tongue of the square. Make a mark of this length on the edge of board. Now take the width of A to D ([Fig. 84]) which is 6 inches off the blade; keep this 6-inch mark fair at the end of this line made on the board ([Fig. 81]) and push on square until the tongue touches the end of the line; mark by the tongue, and this gives the bevel required.