Hi,

Any way can make Helix/Spiral curve from ellipse? I know how to make it from circle, but I have a case need make Helix/Spiral curve from ellipse, is it possibel?

Thanks

ping

Hi,

Any way can make Helix/Spiral curve from ellipse? I know how to make it from circle, but I have a case need make Helix/Spiral curve from ellipse, is it possibel?

Thanks

ping

Don't know why I didn't think of this earlier, but if you don't need a perfect ellipse, don't forget the trusty curve thru xyz points.

I've found that for many purposes just four points around a circle, or in this case an ellipse, will yield a curve that is pretty close to the exact shape. The exceptions being the ends, which can usually be "tweaked" by adding a few extra points, or just cut off the offending part. Sometimes it's quicker to generate a big set of points with a spread sheet (auto-fill is your friend) than to make reference geometry. And, once you have a spreadsheet with your point set, changing it to get different sizes or proportions is very easy. In the examples here it would be a simple matter to adjust the x and y columns to make a tapered "helix" or the z column to make a variable pitch.

With a little thought (and a pencil) it's often easier to come up with the xyz points for a curve, than you might think at first glance. It usually takes fewer than you think to get "close enough", even for seemingly complex shapes.

In these examples note that the sketches of ellipses are just to show how close (or not) the curves are to true ellipses. The curve geometry is from imported .txt files. I attached the xyz point file for the red curve.

Two curves through x,y,z points,

Comparison to true ellipses, sketches 2 & 3 showing.

Here is a Microsoft Word file explaining what I did, with some images attached. This file can be manipulated to whatever size ellipse you need, as well as pitch and number of coils.

I just notice that the formulas were wrong, thats what I get for cut and paste, they should be 0.25 and 0.5 and 0.75 not 1/3 and so on...This method works for square and rectangular springs/helix as well.

Rusty,

Nice solution, and the description is above and beyond.

Kelvin,

I can open your files fine, also a neat way to go.

Pete,

I figured someone out there would know an equation. Seems to me that's the way to go, for folks who remember more trig' than me anyway.

Ping,

I sure hope one of these solutions works for you.

There is another way to use trig to create an elliptical helix that is a little easier to control:

Useing for example Sin(x) for one axis and 2*Cos(x) for the other axis you can create the ellipse. Verying "x" will give you the number of coils and X1 and X2 is the start and end point (height of spring).

The image below shows the first axis:

The next image shows the second axis perpendicular to the first:

Now that you have the Sin and Cos curves, you'll need to project them onto eachother (Insert --> Curve --> Projected --> Sketch on Sketch):

Yes, but you will have to use an elliptical extruded surface cylinder and a helical swept surface.