February 17, 201313 yr We all know to use a piece of string to draw an ellipse But what is often left unsaid is how to get that string length just so, to create the ellipse of a specific dimension One Dimension from the ellipse is taken to the steel square: AB (the minor axis) is found marked one leg of the steel square. BC (the major axis) is used as the distance to locate the third dimension AC by finding where the line intersects the other leg of the square from AB (see the red line on the square in the picture). The red line is BC. Where it intersects is AC that is the length between the two focal points along the major axis. So now you know the length between the two focal points points. Now to find the length of the string you simply add  the dimension for AC with BC So in the example minor axis AB is 9" The major axis BC is 10" The solution found on the square 4.3589"  Yah you can really locate to 4 decimal points on a square huh? OK maybe not, but that's the least of your worries if you want high degrees of accuracy when working with string. Anyway the string length is 10 + 4.3589 = 14.3589 Now all you have to figure out is how to tie a string to 4 decimal places.
February 17, 201313 yr I usually do it with the Sketchup add on and then print it full size. Although, that sometimes requires "cut and tape".Lew Kauffman-Wood Turners Forum HostTime traveler. Purveyor of the world's finest custom rolling pins!
February 17, 201313 yr  I use three points. Two for nails, and the third is out on the side.  Then I just tie the string into a triangle shape, and spin the pencil along with the string. Gets a bit complicated, though, when one has a "straight stretch" in between the two ends.  ( not really, just needs to be done a little differently, is all)Planer? I'm the 'planer', and these are what I use...Planer? I'm the 'planer', and these are what I use...
February 23, 201313 yr i like the formula but i usually just tap two nails and trial and error.The CLEAVE books site has a bunch of different math problem fixers ( sq. feet, bushel to ounces, cone area) that are fill in the blank and it does it for you.By the way, 2 nails at 7 and .15 inches (engineers scale) apart, tie the string, pull the nails and your set.
February 23, 201313 yr Author well, it is just string. But they used a lot of string to build the world's ancient and great engineering accomplishments.
February 23, 201313 yr Thanks for the info Cliff. I'll test your work the next time I need to draw an ellipse.Ron DudelstonSite AdministratorAbove and Beyond WoodWorks
February 23, 201313 yr  No measure method:Lay out the center lines in each directionUse a pair of dividers, from the point where the two center lines cross to the edge of the pieceSwing dividers until they mark the long axis center lines, do this from both sides, to get an "X" markPlace one nail in each crossing point. Place one nail out on an edge, doesn't matter which edgeTie a length of string around all three nails. Remove the nail at the edgeReplace that nail with a sharp pencilKeeping the pencil upright, use the string to guide the pencil around the other two nails, while keeping the string taut. Remove string, and the two nails. put pencil back in shirt pocketSaw the piece, just leaving the line, fine tune until all of the line is gone.   Ellipse is done.Planer? I'm the 'planer', and these are what I use...
February 25, 201313 yr Cliff, great job and great tip! And great exhibit!I'll definitely give this a try next time, saving image now for my archives.John MorrisThe Patriot WoodworkerProud Supporter of Homes For Our Troops and Wounded Warriors Project
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