To draw a logarithmic spiral, follow these steps:
1. Draw a line. One of the
ends of this line will be the center of the spiral.
2. Make a 360° circular array
of the line with one of the endpoints as the center and choose the option to rotate the object so they will all be oriented
radially from the center point. The number of lines in this array will determine the angle between the tangent
and the radial line of the spiral. For starters use 20 lines to make a spiral like the one shown in the pictures below.
The angle of the spiral will be equal to one half of the angle between adjacent radial lines. With 20 equally spaced
lines the angle between two adjacent lines will be 360/20 = 18° So the angle of this spiral is 9°. If
drawing by hand use a protractor to draw marks where the radial lines extend and then draw lines through these points from
the center.
3 Draw a polyline beginning at the outer end of one of the lines and use
the perpendicular object snap setting to pick the spot on the next line around and continue this for as long as you like (you
will never reach the center point). Zoom in as needed. If drawing the spiral by hand, use a 90° corner (sheet
of paper, cd case, drafting triangle, etc...) to draw a perpendicular line to the next radial line. Align one edge along
the next radial line to extend the spiral to and move along this line until the other edge intersects the previous line at
its end where it touches the radial line and draw a line segment to the radial line.
4.
Smooth out the polyline using fit (Autocad). Using "fit" will prevent moving any of the vertex points.
