Stange behevior of loft

Math

Hello,

I am currently designing a scoop, using a loft.

The loft is define by :

• A conic (semi eclipse) on a plane parallel to the Right Plane with an offset
  
• A semi circle on the top plane
• A Guide using a line design on the font plane between the semi eclipse and the semi circle

And the result is stange, I obtain a dissymmetry on the loft :

The semi-circle and the semi-eclipse are strictly symetrical compared to the front plane. So I don't understand why I have this dissymmetry on the loft. An when I create the loft, if I reverse the selection order of profiles of the loft, the dissymmetry change of side.

I make a test, designing the exact same loft (same profiles, same guide) but alone (without the first main sketch and the first two extrusion I have in my current desing) and I I obtain a perfect loft without this strange dissymetry.

So I really don't understant  what appen in my design that can conduct to this dissymmetry ?

Thanks !

Math

owen_sparks

Hi Math and welcome. It's easier for people to help if you provide a link to your document. I'm sure someone will jump in and help then. Owen S.

Math

Hi

Here is the link : https://cad.onshape.com/documents/77db6f00683c29b530546088/w/04bb7336e3d16390352f9720/e/a56b4e9c22f8fecff06ef79d

Thank !

Math

owen_sparks

Hi again.
I was able to get it to work by moving your profile sketch onto a new plane with a zero offset from the face it was on.  In theory this does nothing but actually it stops Onshape automatically using geometry imprinted on that face.  I'm not 100% sure that was what was going on here but it works 

Link here



Cheers,
Owen S.

Math

Hello,

Thanks, It works like this ! But I really don't understant the Onshape Behavior for this case and the need of a new plane !

Math

lana

I think we can improve that behavior. I grabbed an issue on it. 

Math

Hello

Thanks for you answer lana.

I'am here again because there is an other behavior of my loft that I don't understant again.

Waiting the answer oven_sparks, to get around the problem I mention before, I had add guide for my loft (Using 3D fit splines) :

So I carry on my design of scoop. And at the finishing of my design and make a smooth leading edge of my scoop, I use the Fillet function (see previous picture).

Link to this design : https://cad.onshape.com/documents/77db6f00683c29b530546088/w/04bb7336e3d16390352f9720/e/e1ddfe89bdfabb93296708f0

After, I make a second part studio I restart the design of the scoop using the tips given by owen-sparks. As I said before, I works for the loft.

But when I try to finishing my scoop with a smooth leading edge (like the previous one), the fillet function doesn't works ! And I don't understand why because event if the method to build the scoop is different, the result is the same. But the Fillet function doesn't work !

Link to this design : https://cad.onshape.com/documents/77db6f00683c29b530546088/w/04bb7336e3d16390352f9720/e/315fd23d322fe9f1d745b827

So, any idea what appens now ?

Thank a lot !

Math