How to change the "arc" of an ellipse?

kay_bursig

Hallo.
When sketching an ellipse you can change the witdh and hight. But I need a defined "arc" so to speak. Can I define 2 points on the ellipse and squeeze/stretch them and keep the ellipse proportional?

Thank you very much.

S1mon

Not sure I understand what you're trying to do. A picture would probably be worth the proverbial 1000 words. 

That said, would a conic section help?
https://cad.onshape.com/help/Content/conic.htm

Or perhaps you need a full ellipse and you're just trying to control it with points on the ellipse, which you can do:

glen_dewsbury

Are you meaning something like this?

https://cad.onshape.com/documents/cb2bcd844a298bdf747100bc/w/98472c696ada5bf510cb4476/e/397321d3379cb36e4008c606

kay_bursig

Yes you both got it. When I add 1 point to the "arc" I can change the look of the whole ellipse. If I add a second point it won't allow me to change the value. Instead of changing the "arc" it changes the position of the point.

What I need is: the middle point with 2.4 is correct, the left point (where it says 1.933) has to be 2.3 at that X coordinate

S1mon

@kay_bursig

Those points are missing any x dimensions. The center point is also not fully constrained. Try working with "Show constraints" turned on. It may help you understand what's going on.

kay_bursig

Ok, I tried it wth constraints. If I change the x value from your "2" to more, the whole ellipse grows. Let`s say instead of your x=2 I take 4.5 and instead of my 1.667 we take 2.3 ... I dont get it to work look like in my sketch.

eric_pesty

@kay_bursig
That wouldn't be an ellipse anymore!

If you want a shape like this maybe use a spline instead (and mirror it if needed)?

S1mon

@kay_bursig

Your sketch implies something which can be done with a conic or splines, but not a true ellipse. I'm still not sure what you're trying to do, but is this closer? Unfortunately, Rho is required in Onshape. It will not solve for Rho, so I had to iterate to get something closer to the proportions you have in your sketch.

kay_bursig

Aha, so there's the problem   I'm autodidact, so these basics I missed. I want to 3D print an adapter, thats what I need it for.

I tried it with the conic and mirrored it. That works.

Thank you guys very much!