Would appreciate some help with "MergeAllFaces" command

I’m new to Rhino and I’m working on my first 3D model. I’m at the point where I need to MergeAllFaces but for some reason I’m experiencing some issues. When I use the command “MergeAllFaces” some surfaces disappear.



From what I understand, this is because they are coplanar surfaces. I’m hoping to be able to merge them together into one poly surface and have them not disappear. If anyone could help, that would be great. Thanks for the help in advance! I’ll go ahead and attach the rhino file that I have been working with. MergeAllFacesHelp.3dm (4.6 MB)

Hello - the object has some non-manifold edges - these can make a mess of the topology - my guess is that is what is happening here - non-manifolds are where there are more than two surface edges joined in one location -

As you can see it is possible and legal in Rhino but generally a bad idea


Thanks for the reply. Now I see the non-manifold edges. I’m unfamiliar with what those are so what would be the best way to go about fixing them. Is there a way to get rid of them without changing the shapes that I have created?

Hello - the way out is to ExtractSrf the faces all around the edge and Join them into the ‘correct’ sets:


then Join everything back up. You may or may not always get a valid solid arrangement though - here it looks like you will - these are all four-surface non manifolds that can be split into two pairs.

Looks like you may still end up with some reversed faces though… (= invisible in shaded views) The right way to build this is not to have zero-thickness in a single solid - ether leave a small gap the these coincident edges or have them fully intersect, and trim/Boolean them.