Creating a shell of a co-concentric ellipsoidal funnel

tony_g

Hi, I'm not a pro, so please bear with me:  I'm trying to design a shelled elliptical funnel to 3D print.  First, I drew an ellipse, than an inside ellipse, offset it by some distance, extruded both into thin plates, created a loft, but whatever I try, I can't create a shell of the side wall...  What am I missing in the process?  Here's a link:  https://cad.onshape.com/documents/067a75c86a3cee77816cd1e7/w/5acf727f54a0abd5b6964163/e/16c2311f5029314b542f229d

MichaelPascoe

Try using the shell feature. It will be perfect for this.

bruce_williams

@tony_g

@MichaelPascoe shows a couple nice tricks.  First you can just sketch one ellipse and then extrude with draft (if the side angle is consistent all around). Or if you need to sketch top and bottom, do the base as you did, then make the top on a mate connector or offset plane at the top location.  Then Loft is done between the two sketches (no need to make offset surface as you have.) 

The 2nd thing Michael shows is a slick way to make return flanges with first Shell at 1/2" then next for .1" wall.

Finally, you may be having problem with Shell because your offset surface is showing. You need to select the face of the solid in Shell.

tony_g

Thank you both very much for your quick and excellent help; the problem has (almost) been solved!  :-)

One issue I still see is a zero-thickness "membrane" in the top ellipse; it shows up in the STL file, but doesn't print as there's no thickness assigned to it.  Was the "Extrude-Funnel" name added, or is it a function I can't find?  I suspect it's got something to do with the shell thickness being added outside, instead of directed inside the part.  Same thing I noticed with Fillets applied to edges of thin plates--they add to a new, larger dimension, something I would not expect this operation to do.  But I'm just a retired chemist...

MichaelPascoe

I'm not sure about the zero thickness. The shell feature should let you set the shell thickness to whatever you like.

It is a standard "Extrude" with a draft angle selected. I like to re-name the features something relevant for easier sorting when working in complex studios.

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bruce_williams

@tony_g

You are probably exporting from the Part tab and getting your upper 'Offset surface 1'.  So either delete that surface or export by right clicking the 'Part 1'.  And next time you can build this without the surface at all...