EZ Ellipse

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EZ Ellipse

Postby Harold Sultzbaugh » Fri Sep 12, 2008 11:29 am

For simple instructions on making an ellipse; go to;
'benchnotes.com'
scroll to' information'
click on 'laying out an ellipse'
Nothing to it!

ILLIGITIMI NON CARBORUNDRUM!!!!! :frustrated:
CMTears
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Postby cambi » Fri Sep 12, 2008 11:47 am

Interesting!! Good find!!
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Postby mikeschn » Fri Sep 12, 2008 3:25 pm

Andrew taught us about the two nails and a string. You can see me doing it here...

Image

Mike...

P.S. I wonder where Andrews directions are? Ah, here they are:
http://www.angib.pwp.blueyonder.co.uk/t ... tear80.htm
The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...
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Postby DBizer » Fri Sep 12, 2008 6:41 pm

The link below is a handy "tool" to use with the string method of drawing ellipses. I've been using for a couple of years now and it sure saves a lot of time find points and string length.


http://www.cleavebooks.co.uk/scol/callipse.htm


David
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Re: EZ Ellipse

Postby gdpipkorn » Sat Apr 05, 2014 7:20 pm

David, Thank you for this invaluable link to "cleavebooks". An amazing tool.

Grant
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Re: EZ Ellipse

Postby Glenn Butcher » Sat Apr 05, 2014 7:47 pm

The javascript tool I wrote gives the coordinates and string length for ellipses:

http://pulpitrock.net/profiletool

Select the "All" radio button and, ta-da...

MrMatt used it to draw his profile: viewtopic.php?f=50&t=59414#p1072668
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Re: EZ Ellipse

Postby Corwin C » Sun Apr 06, 2014 1:01 pm

Here's a different method that doesn't require strings, focus points off the edge of your plywood, or special software or math to figure lengths. It's an old-school way of drawing an ellipse as well as some other challenging shapes as well.

First, lets start with an ellipse ...

An ellipse is a curved shape which has a major axis and a minor axis 90° from each other. The curve is tangent to the axis (meets at 90°) as well. This enables a smooth transition to a line when the line is at a right angle to the end of the axis. For example ...

Image

This image shows a blue line and a red line that may be connected smoothly by an elliptical curve without any bumps, lumps, or bulges. To do this, build a trammel. For my trammel I picked a piece of heavy cardboard that is a little bit longer than the major axis. I then placed a stylus (marking device) in one end. In this case it's a mechanical pencil. Then I put two additional points at the exact distance from the stylus for the length of each axis. In this case they are silver pin heads. Here's a picture ...

Image

It is hard to see in the picture, but the pencil is at 0, there's a pinhead at 77 and another pinhead at 134. In actuality, I didn't measure those distances, I just held the trammel on the axis and placed the pin at the appropriate point. An important point here is that all three are in a straight line. Next, we need a guide for the pinheads to follow, so I used another piece of cardboard that has an accurate 90° angle ...

Image

Notice the placement ... the guide follows the major axis and is an extension of the minor axis. In this picture it is bigger than it needs to be. It only needs to have sides as long as the difference of the two axis. Also, it doesn't have to be a solid piece, it can be anything that give you straight line guides. In real life, I often just clamp a framing square in place. Next we use the trammel to draw the curve ...

Image

Carefully sliding the pinheads against the guide, the stylus will scribe an accurate elliptical curve. And here is the result ...

Image

Now for something more challenging ... I am planning on building a Benroy style teardrop, however, I want it to "lean" toward the tow vehicle. In other words, the two flat planes (roof and front wall) are not at right angles to each other. Here's an example ...

Image

Notice that the red and blue lines are at an angle with each other and the axis lines no longer meet squarely. I drew these to the same dimensions as the first example so I could use the same trammel. However, I need a new guide that looks like this ...

Image

Notice again here that the guide follows the major axis and is an extension of the minor axis. Use the trammel just like before ...

Image

And the resulting curve ...

Image

For some reason the picture is upside down, but you get the idea. Personally, I find this a whole lot easier than stretchy string, odd measurements, and so on, plus it has the advantages of smoothly transitioning between any two curves or lines.
Corwin
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Re: EZ Ellipse

Postby ctstaas » Sun Aug 31, 2014 4:59 pm

Thanks Corwin and super cool, I needed to draw an ellipse the other day and could not remember the string thing and it was easier to just free ball then to try to look it up so your method is perfect and I promise to never forget. I was an iron worker/ fabricator for 30+ years and did all of our layout "Old School". And your method is like a tool and a machine both, at the same time. I have a strong need to draw an ellipse now.
Enjoy, Chris
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Ellipse instructions for Sketchup and string

Postby ChasCABQ » Tue Oct 07, 2014 7:52 am

Here's set of graphic instructions for drawing an ellipse with string: http://www.mathopenref.com/printellipse1.html

I also made an ellipse in Sketchup by first making a circle with smaller radius then use Scale tool to make one axis longer. Surprised how close it turned out to be my combination of two arcs with different radii.
Build journal: http://www.tnttt.com/viewtopic.php?t=61303
In 2016, I received a kidney transplant, finished my teardrop, and took it on the road! In 2017 I sold it and am back to car camping.
Thanks to all forum members who provided advice about my build and posted info to help me get started.
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Re: EZ Ellipse

Postby Glenn Butcher » Tue Oct 07, 2014 8:47 pm

My profile tool will display the foci coordinates and the string length for an ellipsis, just lay out each of your quadrants and click All... http://pulpitrock.net/profiletool
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