Hi Danny, thanks for the detailed testing of the new face extrude!

> The file attached looks like the image below, when you extrude the face that is style
> 'Red' in the Z+ direction and end up with the result like in the second image the body
> becomes a joined surface.

This is because it forms a "non manifold" edge, basically after that cut there is now a spot on the model where 4 different faces are coming together at a single edge, it's sort of like the model has a pinched area in it where opposite sides of the model are touching each other. That more or less makes it into a self-intersecting shape and there will be problems with analyzing the volume of things like that.

In your case here it's this particular spot here, notice how opposite sides of the model are coming into that same one edge, that's a type of self overlapping:



That's more or less a case of just "don't do that"... There needs to be a little bit of clearance space in spots like that rather than having opposite sides of the shape come to a single touching edge.

Even though there aren't any naked edges in that model, it doesn't read as a "solid" object type because there is an error classifying the solid volume regions of it. Something will only read as a solid if it both has no naked edges and also has been able to form at least 2 region volumes for the outside region and inside region. EDIT: actually after double checking, this particular case doesn't read as solid not because of regions but because of that one particular non-manifold edge which ends up belonging to 4 faces. A manifold edge must belong to only either one same face for a closed surface or otherwise be joined between just 2 surfaces, all edges must be manifold for an object to read as solid).

If you widen this spot here over just slightly then it should avoid the grazing pieces and then your same red face extrusion should generate a solid ok after that, see the attached 3DM file.



- Michael