ABC of the Steel Square and Its Uses

by Fred. T. Hodgson

Fig. 82.

Fig. 83.

To obtain an example of unequal pitches refer to [Fig. 84]. To set this out, run a line parallel off the edge of the board, and off this line square another. With the intersection A as a center, describe a semi-circle of 6 inches radius. This indicates the center of the rail. Run lines radial from A as shown; these are the riser lines. Draw the lines B C and C D, which are the tangents. Draw the diagonal B D. To make the bed blocks, procure a piece of one inch stuff; take it to the width shown at B C; square on a mark about 3 inches from the end (this is to allow for the shank to clear the saw table; the block is shown at [Fig. 83] without the 3-inch allowance). Take on the steel square the rise on tongue and going on blade of the straight flight of stairs; mark on the inch board at tongue; this is pitch of the first tangent. Take the height at D, which is one and a half risers—10½ inches; deduct the height of the first tangent from 10½ inches; take the difference on the tongue and width from C to D on the blade; the tongue gives the cut for the second tangent. Mark the pitch of the first tangent on the edge of the second and cut to this; the pitch of the second tangent gives the edge cut of the first. Cut and fix together with stretcher as previously described.

Fig. 84.

To get out the face mold, procure a piece of thin stuff. Three-ply wood is excellent, as though it is liable to warp it does not shrink perceptibly. Shoot on edge and gauge on a center line; take the distance from B to D ([Fig. 84]) (the hypothenuse of 6 and 6) on the blade and the rise (10½) at D on the tongue; lay on the edge of the board to this. Lay off this length on the three-ply at B D ([Fig. 82]); take the width B C ([Fig. 84]) on the blade, rise at C on the tongue; find the hypothenuse, and apply with a pair of compasses at [Fig. 82] with B as a center cutting at C. Then apply at D as a center, cutting at A. Now find the hypothenuse C to D ([Fig. 84]), and apply the compasses as before, with D and B as centers, cutting at A and C. Connect up the points where the arcs intersect to B and D; this is the face of the inclined prism, and contains the true shape of rail. Continue the tangent line C B, 3 inches or whatever is required for the shank, and square the joints of the lines B and D. In order to locate the major axis the horizontal trace is now required. Stand the bed block on the plan (see [Fig. 83]). Run the blade of the square down until it touches the board; mark this, and remove the block. It will be seen that the bed block has not got the 3 inches allowed at the bottom, but the horizontal trace is as easily found with as without the allowance; all that is required in the former case being to turn the blade to B (still keeping the heel at the top of the bed block), make a mark where the square touches and lay on the square as shown at [Fig. 83]. Mark at the blade, and slide back the square until the tongue touches at B, and also at the center A. This gives the true horizontal trace and major axis. Note the size indicated by the arrow lines on the tongue (from heel to B). Transfer the square to the three-ply board ([Fig. 82]), placing it as shown, with the blade touching A, and the distance of the arrow lines at B. Mark along the inside of the blade of the square and slide the square back until the tongue cuts at A. This gives the minor axis. Now continue this line downwards to guide the position of the square shown at [Fig. 84]. Describe a circle as wide as the rail on the minor axis ([Fig. 82]). The distance from A ([Fig. 84]) to the center of the rail is the distance to apply at [Fig. 82] for the center of the rail, as this is the point where the center of the rail is fair with the plank. Obtain the width of the face molds, and apply at B and D; lay the square on the major and minor axis as shown at [Fig. 84]. Lay a lath on the square, with the point touching the outside of the circle at C; drive in a nail at the heel of the square; shift the lath until the point lies at B, and drive in another nail at the side of the square. This trammel is now ready to sweep the outside of the mold, which is done by reversing the square, as shown by dotted lines. Pull out the nails and repeat the process for the inside of the mold.

Fig. 85.

Now run parallel lines off the tangent B for the shank; this completes the face mold, which is now ready for the face of the plank. Wreaths for stairs with flights which stand at either acute or obtuse angles to each other may be set out by the methods that have been here described. The only difference, practically, is that the bed block is made acute or obtuse to suit plan of tangents. The device shown at [Fig. 85] has been found to answer excellently for striking out ellipses. To make this, procure two screws ¾ inches long, also a piece of brass tube that will just slip on the plain part of the screw without shaking. Counter sink out the ends until the screw heads are flush; cut two pieces off the tube three-sixteenths and file up true—these pieces are best held by sinking them with a bit in a piece of hardwood. Now when about to strike an ellipse, drive these screws in with the collars on to half major and minor, measured from the point of the trammel to the inside of the collar for the major, and to the outside of the collar for the minor. It will be found that if the collar has been made true, the trammel will slip around the curve without causing the square to slip about, the collars acting as rollers.