layout tools for ellipse

i'm noob to your forum.
I was wondering about laying out ellipses and very large arcs with a mechanical device. ive seen some type of plastic rule that is able to bend as each joint slides over one another. I have not been able to find out the name of this device or where i could get one or how to make one . i bielive it comes from oldschool boatbuilders. can anyone help me with a link ,a name ,a drawing, anything. i build concrete skateparks and am looking to use something like this for onsite shape building .The shapes you use in your hulls and so forth are very simular to some skatepark elements. any info would be greatly appriciated

thanks

 

If you go to Google 'images' and put in 'ellipses' various tools and ways to draw them come up. Sam

 

Is that total or patial ellipses?

 

Junkdog, try two nails & a loop of string.Regards from Jeff.

 

i was interested in partial ellipses i have used several methods which include string and two points as well as a board with two sliding pivot point that are constrained on the x and y axis but in order to draw a 10-13 foot radius you need a lot of shop space and the aligmen of those point s on a sheet of ply is difficult at best i was thinking of something simple that would be easy to use if it exists thanks for your input

 

If you want to be a really safe Walruss you'd use a pinhole camera.

 

Poida, your right in each case protects the eyes no end, unlike certain people who ain't getting the joke!

 

Have you tried long strips of oak or fir sold as stop trim and a couple of nails?

 

I tried the nails and string a couple of times... seems one has to maintain a certain (precise) tension on the string.... didn't work well for me.

Used the old bent, warped and twisted beam as a model to copy from, clamped it to my workpiece for marking and then cut (leaving extra meat on the cut).
Then planed (scarf actually) the surface proper by eyeball.

Didn't need the pinhole camara either as it was a total elipse of my heart.

 

A way to layout a ellipse is to use two nails and a length of string

 

or get somebody else to do it!

 

That sounds like a good plan.