We are installing an elliptical window on a new house and I need to know an easy way to draw an ellipse. The RO is 3’0-1/2″ X 4’6-1/2″. I used to know how to draw it using a couple of nails and a looped string. Does anyone know or remember the formula?
Tim
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Replies
http://www2.fwi.com/%7Ekrumy/elipse/elipse.htm
Go read that it explains how.
Tim,
You can make an easy ellipse by tying a piece of string to two nails (where the nails are at the foci of the ellipse) and running a pencil around the stretched length of the string. You have to choose the string length/nail position such that the stretched string will end everywhere on the points of the ellipse you want.
I don't know jack about carpenty (I'm working on my PhD in mathematics...) so I'm at a bit of a loss at how I should explain this. lol. The equation for an ellipse is
x^2/a^2 + y^2/b^2 = 1
where a is the semimajor axis (the longest distance from the edge of the ellipse to its center) and b is the semiminor axis (the shortest distance from the edge of the ellipse to the center of the ellipse). Any points x and why that satisfy that equation will fall on the ellipse with those parameters.
(not sure if this helps)
scott
Your points are 1' 8.25" from the center and your string is 4' 6.5".
Been there and tried to do that and then the window when it arrived was a little off. We had to reframe the opening. Just frame a rectangle big enought and plank right over. Take a template from the window when it arrives and work from that.
Hi All,
The method that requires a ruler, compass, string and two push pins is described in the 'Backstage Handbook' published by Broadway press, second edition. In the shop math section, page 182. I will try to surmise:
Draw a major axis line (long dimension).
Bisect with the minor axis (short side at the middle).
Set compass to one half of major axis length.
Place compass point on end of one of the minor axis points.
Strike an arc that bisects the major axis.
This is where the push pins are placed.
Make the string a loop that goes from pin to pin to end of short side.
Put a pencil inside the loop and draw the ellispe.
A long explantation for an easy technique.
Good luck,
Art
Here is a link that demonstrates the string method. I use picture wire when I draw my ellipses. Take your width and divide by 2. Draw a line that divides your opening in half. Then measure up from the bottom of the ellipse and that center line and mark your height. The swing a radius from the top of the arch ( that mark on the center line you just drew) that is equal to half the opening or half the ellipse. So measure 2'3 1/4" and draw a vertical line. Then measure up that line 1'6 1/4" and mark a line. Then swing a radius that is 2' 3 1/4" on both sides of the verticl line. You can swing a circle if you want. At the 2 points where the circle crosses the bottom line of the opening are your foci points. Drive 1 nail at each point and one at the top of your arch loop the wire around all three nails and then pull the top nail and mark your ellipse.
Here is a link that demonstrates how it works. I know you probably remember this, but I typed it out to reinforce it in my own brain. Hope this helps.
http://mathworld.wolfram.com/Ellipse.html