Laying out an ellipse?

[Jon Wilson]

I'm in the process of designing/laying out a carvers lap desk for my wife.

I need to make a cut out so that the desk will snug up against her while she's using it, she'd like an ellipse.

What the wifey wants, the wifey gets...

What's the easiest, simplest way to lay out an ellipse without using a bunch of math (I am NO good at math)

I searched google and there were a few videos but they weren't real clear and/or used a bunch of math.

Thanks!

[Mel Fulks]

For that particular purpose I would use the "string " method. It's easy to find on line and easy to use.

[Mark Kornell]

It is pretty easy, but you can't get away from a bit of math.

The real easy part is drawing the ellipse. For that, all you need is two small nails, a piece of string and a pencil. Make sure the string isn't stretchy.

If you've already cut out the top to the exact size, you will affix the nails to the edge with hot glue or something similarly removable. Otherwise, drive the nails into the top just on the waste side of your cut-off line.

Once you've got the nails set, tie the string into a loop and drape it over the nails. Then use a pencil to trace half of an ellipse as shown in this video: http://www.youtube.com/watch?v=7UD8hOs-vaI

The harder part is knowing where to put the nails and how long to make the string. For that, unfortunately, here comes a bit of math.

First, you need to know how wide the cutout will be, and how deep it will be. Let's say you want it 30" wide and 8" deep.

To do the calculation, there's a web site that will help you: http://www.mathopenref.com/ellipsefoci.html

The site has an interactive piece where you can drag an ellipse to your desired width and height. Actually, the web site uses distance from center, which is half the total width and height. So, for this example, I will drag it to 15 and 4.

This gives an F of 14.5. For the math inclined, the formula is sqrt(abs((W/2)^2 - (H/2)^2))

Using this number, the length of your string will be F + F + W. (Or F*2 + W) In english, take the number this web page spits out and multiply it by two. Then add the overall width of your desired cutout. So, 14.5 + 14.5 + 30 = 59. Add a little bit at each end to account for a knot. I'd add 2 inches, then cut the string at 61". Mark off 1" at each end, and tie the ends together at the marks.

Next, fix the nails. Mark the center, and then measure F" left and right (14.5" in this example). The nails get fixed at these two points.

Then, loop string around the nails and draw out the ellipse as in the video. Well, half the ellipse. Cut to the line.

If you know your width and depth and want help with the math, post here or PM me.

[Steve Peterson]

Drawing an ellipse is relatively easy with 2 pins and a piece of string. Experiment on a piece of cardboard to see if you can find a shape that you like.

I find that true elliptical shaped tables are too pointy on the ends. Maybe you could use 2 half circles separated by a rectangle. This gives more area into the corners and is super easy to draw.

Steve

[Tom Fischer]

I've done it without too much trouble, pretty accurate.
I've used the trammel method (make it out of scrap), and need one framing square.
This covers it.
http://www.youtube.com/watch?v=J48e1mVQ_Sg

[Prashun Patel]

2 pins and a string works. You'll need some string that doesn't stretch, though. 0.

[Dave Zellers]

I've done it without too much trouble, pretty accurate.
I've used the trammel method (make it out of scrap), and need one framing square.
This covers it.
http://www.youtube.com/watch?v=J48e1mVQ_Sg

I was just about to post that video. The trammel method gives perfect results while the string method is iffy.

Instead of using a framing square, set up a 'T' with straight scraps and leave a small gap at the top of the vertical leg for the nail to slide through.

That way you can draw the entire half ellipse that you want without stopping.

To set up your trammel place it on top of the vertical leg of the 'T' with the pencil at the position you want above the horizontal (long axis of the ellipse) 'T' member. nail a small brad through the trammel exactly at the bottom edge of the horizontal leg of the 'T'. Now slide that nail to the left and swing the bottom of the trammel up to be in line with the horizontal (top) leg of the 'T' and when the pencil is at the width you want, drive a brad through the trammel in line with the left edge of the vertical 'T' member.

Now draw always keeping both nails rubbing along the bottom and left sides of the 'T'

Fool proof.

[Mel Fulks]

I always use the trammel method for architectural frames and then scribe out,in ops case ,where it seems there is just an edge, still think string is easier.

[Joe Scharle]

I simply mount a 1/2" spiral upcut bit in a router attached to my ellipse jig and swing & adjust until I have the ellipse (actually an oval, but close enough) of the size I'm looking for. Here's a pic.

257561

[Jim Tabor]

Jon Wilson,
You can go to John Wilson's shakerovalbox.com site and learn the string method.