PLATES [B-V--3-a], [B-V--3-a’]. DOUBLE GROOVE SPIRAL. STRAIGHT SHAFT

To work out the double groove spiral for the magazine holder illustrated, proceed as follows:

1. Square up the stock to 1⅜". Center carefully and turn the design on both ends as shown, in the upper diagram (Plate [B-V--3-a’]). Turn the cylinder between the top and bottom, making it 5½" long and 1⅜" in diameter.

Fig. 26.

2. Divide the cylinder into two equal parts. Each part represents one revolution of the spiral.

3. Divide each half into four equal parts as shown in the top and center diagrams (Plate [B-V--3-a’]), 1-1’, 2-2’, 3-3’ and so on. The proportion of the distance between these circles should be one-half the diameter of the cylinder.

4. Draw lines A-A, B-B, C-C, and D-D, parallel to the axis of the cylinder 90° apart.

5. With a band 3/16" wide of any substantial material (preferably a narrow strip of tin or a watch main spring) begin on the line A-A at circle 1, and connect circle 1’ at line B-B, and then connect circle 2 at C-C, and so on until the spiral is made the entire length. Mark on both sides of the 3/16" band so as to keep the spiral parallel.

6. Next begin at the line C-C where circle 1 crosses it and connect from here to 1’ at B-B. Proceed as in Step 5, as shown in the center diagram.