This section is from the book "Modern Shop Practice", by Howard Monroe Raymond. Also available from Amazon: Modern Shop Practice.

Draw a circle with the center at O and a radius of 1 1/2 inches. Locate twelve points, 1/8 inch apart on the radius 0 A and draw circles through these points. With the 30-degree triangle, draw radii OB, 0C, OD, etc., 30 degrees apart, thus forming 12 equal parts.

The points on the spiral are now located; the first is at the center 0; the next is at the intersection of the line 0 B and the first circle; the third is at the intersection of 0 C and the second circle; the other points are located in the same way. Sketch in pencil a smooth curve passing through these points.

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