receiving error message when extruding and I don't understand what it is trying to tell me,

charles_greenacre

receiving error message when extruding and I don't understand what it is trying to tell me, in other words, I can't figure out what needs changing to fix the issue.
The error message is "Boolean operation failed to return a part".  when I extrude as new, the new part creates successfully. when I try to add the new part to an existing part, that's when I get the error message.  I've checked for interference when creating two parts and there are none.  The two parts share a common plane/face.  Also the screenshot shows one surface as being red, and I don't know why it is color coded red.
Thanks

MichaelPascoe

This can happen when a vertex is being shared by several faces. Try overlapping the parts, or make sure there are no shared vertices:
If it is still broken and you can't get it to work, you can share a link do your document and we can troubleshoot it with you.

https://cad.onshape.com/documents/b4fe21b832ecc3ba8a8ae266/w/1cce0e794147413d5c6af952/e/9eb41c6cd739ab8b19bd

NeilCooke

Probably non-manifold https://forum.onshape.com/discussion/comment/66817#Comment_66817

MichaelPascoe

This can happen when a vertex is being shared by several faces. Try overlapping the parts, or make sure there are no shared vertices:
If it is still broken and you can't get it to work, you can share a link do your document and we can troubleshoot it with you.

https://cad.onshape.com/documents/b4fe21b832ecc3ba8a8ae266/w/1cce0e794147413d5c6af952/e/9eb41c6cd739ab8b19bd

NeilCooke

Probably non-manifold https://forum.onshape.com/discussion/comment/66817#Comment_66817

charles_greenacre

Michael, I tried  your solution first, and I had to extrude both sides of the stairs into the stair well before it would work.  Neil, I haven't looked at your answer yet, but will do so

charles_greenacre

Neil, I'm pretty certain that your thought " there isn't a boundary of 0 thickness between the two" applies in this situation, right at the very edges of the part (after it was extruded).  Thanks for the technical explanation.  As we say in W.VA I l'arned som'thin'!!