Can't seem to extrude shapes if they share a point?

Cobalt_Echo

Honestly, I'm not sure how to explain this, so I've attached a picture that probably explains this better.  I can extrude either ONE of the two shapes, but it wont let me extrude BOTH.



Doc: https://cad.onshape.com/documents/195c5cb7be647ed6d778a16e/w/4e7ad5fb64271a128f3dd9e0/e/2d72f4040d431afc617a558b

alnis

That is what is called non-manifold geometry. Onshape's modeling kernel, Parasolid, does not allow such geometry. You'll find the same error in SolidWorks, Solid Edge, NX, and any other CAD system that uses Parasolid.

A good way to think about why that sort of edge is not allowed is what would happen if you added a fillet? Would the two blocks join, or would they be separate?



Also, when you manfucature this part, will there be a small gap or a small amount of material joining the parts? This sort of perfect edge shared by four faces is not possible to manufacture.

imants_smidchens

if you'd like to potentially save time in the future with similar modeling situations, you can use this featurescript:
https://cad.onshape.com/documents/95c00401c440b44ad8799ef5/w/1f1ebce01a3b8eb6fa102975/e/a7c66fe2275987e0c4b83b9a

just keep in mind this will generate two parts as though you extruded each section one at a time.

alnis

That is what is called non-manifold geometry. Onshape's modeling kernel, Parasolid, does not allow such geometry. You'll find the same error in SolidWorks, Solid Edge, NX, and any other CAD system that uses Parasolid.

A good way to think about why that sort of edge is not allowed is what would happen if you added a fillet? Would the two blocks join, or would they be separate?



Also, when you manfucature this part, will there be a small gap or a small amount of material joining the parts? This sort of perfect edge shared by four faces is not possible to manufacture.

imants_smidchens

if you'd like to potentially save time in the future with similar modeling situations, you can use this featurescript:
https://cad.onshape.com/documents/95c00401c440b44ad8799ef5/w/1f1ebce01a3b8eb6fa102975/e/a7c66fe2275987e0c4b83b9a

just keep in mind this will generate two parts as though you extruded each section one at a time.

Cobalt_Echo

alnis_smidchens said:

That is what is called non-manifold geometry. Onshape's modeling kernel, Parasolid, does not allow such geometry. You'll find the same error in SolidWorks, Solid Edge, NX, and any other CAD system that uses Parasolid.

A good way to think about why that sort of edge is not allowed is what would happen if you added a fillet? Would the two blocks join, or would they be separate?

Also, when you manfucature this part, will there be a small gap or a small amount of material joining the parts? This sort of perfect edge shared by four faces is not possible to manufacture.

Good information, thanks!  I plan on 3D printing this, and it checks for non-manifold edges, so appreciate the heads up.

nick_papageorge073

imants_smidchens said:

if you'd like to potentially save time in the future with similar modeling situations, you can use this featurescript:
https://cad.onshape.com/documents/95c00401c440b44ad8799ef5/w/1f1ebce01a3b8eb6fa102975/e/a7c66fe2275987e0c4b83b9a

just keep in mind this will generate two parts as though you extruded each section one at a time.

I've run into this a few times myself. Where I have two separate parts that share an edge (not a point), and I draw them both in one sketch. I have to extrude them as two features. Not a big deal, but just an extra feature. I may check this featurscript out. Thanks.