Extruding beside an edge

mackenzie_bonney036

I'm fairly new to Onshape, so I'm not sure if I am explaining this correctly. My students are creating puzzle cubes and we are struggling to create certain shapes that require an extrusion that hits the edge of another part of the shape. It only works if we do a "new" extrusion instead of adding onto the existing one, which we don't want. I'm sure this is an easy fix, but I can't seem to find an answer anywhere. 
https://cad.onshape.com/documents/e9f0e4292ad89907f19a706e/w/a931088c9dbe258ba586b4f9/e/d6291ad707ace1f9c06d9b55?renderMode=0&uiState=63e3b974b7fb7508c18bbbb0

_anton

Welcome to the forum! Here, you're trying to create nonmanifold geometry, which isn't allowed. You wouldn't be able to physically create such geometry.

If you need something approximating this, you can create multiple blocks, use the Move face tool to add a small offset, and then boolean them together.

S1mon

If you're actually making these as real parts (3D printed or otherwise), you might want to put small fillets on all the corners, and consider the tolerances on the parts in order for them to fit together (i.e. you'll need gaps between them based on your production method). Even if you were wire-EDM and/or grinding the parts out of tool steel, you'd probably need gaps of 10-50µm (0.0004"-0.002").

eric_pesty

You could also create them as separate parts and create a composite at the end to "group" them into a single entity instead of making them a single actual body.