Extruding up to surface with hidden area

gauthier_östervall

This is a minimal example: https://cad.onshape.com/documents/f2056bc8a4f21f6dc05c0aaa/w/db5173e0d0b77e5474e5fa42/e/bfaac868460e035bc6c0abf4

I have a surface with acute angles, which I project to a plane in order to extrude from the plane to the surface. The acute angle of the surface make the extrude fail, which I can understand. How would you go about making this work? Extrude all that is see-able from the plane in several steps, then fill in the gap? Isn't there a more elegant solution?



Here is where I extrude. The volume under the acute part of the surface, where there are three faces stacking up over the sketch, seems to be where the extrude fails (see Origin):

steve_shubin

@gauthier_östervall

https://cad.onshape.com/documents/24fcf2bbbaebe74e0195dc63/w/d7ee1cbaeadcaa16c0c4f6a9/e/833f8267778ddcb3089b1e2b

Maybe this will work for you
You might want to look at both parts studios

owen_sparks

How about extruding above the surface and then use using the surface to split the part, followed by discarding the top part created by the split?
Owen.

NeilCooke

Thanks for the image, saves me opening the doc  This is where your problem is:


If you are trying to "add" these together, it will create non-manifold geometry (a solid cannot have coincident edges or vertices with zero volume).

steve_shubin

@gauthier_östervall

https://cad.onshape.com/documents/24fcf2bbbaebe74e0195dc63/w/d7ee1cbaeadcaa16c0c4f6a9/e/833f8267778ddcb3089b1e2b

Maybe this will work for you
You might want to look at both parts studios

gauthier_östervall

NeilCooke said:

Thanks for the image, saves me opening the doc  This is where your problem is:


If you are trying to "add" these together, it will create non-manifold geometry (a solid cannot have coincident edges or vertices with zero volume).

Thanks for the reply, you had me read about non-manifold. 
The image shows the extrude that works, though. It stops working when I add the middle sketch face to the extrude (expecting a manifold volume). Sorry if I was unclear. 

gauthier_östervall

owen_sparks said:

How about extruding above the surface and then use using the surface to split the part, followed by discarding the top part created by the split?
Owen.

I like this! It's outside the box, although I expected an inside the box answer too. 
In this very case it doesn't cut it entirely since the upper side of the surface doesn't expand to split the volume, but that might be enough for my real project. 

I would expect the extrude to work as is, and go to the bottom of the surface. 

tim_hess427

The easiest method would probably be to do two separate extrudes and merge them together. Do one up to the top surface (area A), then do a second that goes up to the bottom surface (area B ) .