Old-time way to make a Parabolic Curve using a string to draw parabola --------------------------------------------------------------------------------- To: Subject: [SOLAR] Correction to using a string to draw parabola From: "Rich DeMartile" Date: Sun, 10 Jun 2001 20:03:34 -0700 Reply-to: solar-concentrator@cichlid.com Sender: solar-concentrator-errors@cichlid.com --------------------------------------------------------------------------------- Sorry for the error in the original message. I was incorrect in how the string is to be attached. Changes are shown in item 7. Also a new picture is attached. To draw a parabola with a pencil and string... 1. Lay out the axis, the focus, the vertex and the directrix in the proportions you want. 2. Drive a nail or pin into the focus. 3. Temporarily nail down a straight board perfectly parallel to the directrix. (either on the line or just above it.) 4. Lay a large carpenter's square against the bottom edge of the temporary board (or you can make/use any size square you want 3,4,5 of any unit of measurement will give you a perfect 90° square) 5. Align the Left vertical edge of the square against the axis (and nail or pin) 6. Tie an eye to one end of the string and slip it over the focus nail/pin. 7. Place your pencil on the vertex point, and pull the string snug around the tip of the pencil and attach the free end (tape/clamp/tie knot etc.) to the bottom of the square along the axis edge side. (Your main difficulty now is to keep the string snug and the pencil against the square, while an assistant slowly slides the square along the directrix) You can look at the attached picture for a clearer understanding. Now you're only limited by the length of the string and size of the square you use.