Clean from internal edges and faces

Question

1 month blender newbie question. The first one I ask, because can't google it right.

I've created a drawer knob by duplicating and rotating 4 ovoids and later joining them together. It is visually really nice and was very simple to make, but when I look at it in edit mode I see it's a mess. Now I understand I had to use Boolean modifiers in the first place, which I didn't, but that is past now. What I can't understand, is there a simple way to clean it up?

If it was something simpler, I could manually fix that by moving and deleting vertices and edges, but here I have thousands of edges and vertices.

My thoughts are that I could have deleted internal faces by selecting them by trait. But all the intersecting faces didn't create edges, thus, as I understand, the program interprets it all wrong.

UPDATE 16/02: so I've found out how to simply create edges on all the intersecting faces. With automerge and Split Edges and Faces options enabled one has only to select all and move a bit. The result is far from perfect, but it is working. Unfortunately, it does not solve the main problem with internals since program still does not understand what is internal. I tried Mesh -> Clean Up -> Split Concave Faces and Split Non-Planar Faces, but it didn't help in further selecting inner faces vertices only to del them.

Answer 1

I think you are say that you used a Join operation on the objects -- is why you have all those interior vertices.

You should be able to undo your join operation as follows, so that you can use the boolean instead...

1. put the Joined object in Edit mode
2. Use the menu:: Mesh :: Separate :: By Loose Parts
3. You'll be back to having N original objects
4. Now you can use the Boolean modifier, and perhaps Apply it

Unfortunately, sometime the boolean modifier doesn't work well on some complex meshes.

Unfortunately, using a larger object with a shrinkwrap modifier doesn't create the concave surfaces you'd need to project a new objects onto your destination object.

Answer 2

If you want to try this in geometry nodes here's the nodes to get rid of internal geometry.

(Left to Right)

The 1st image is the original image with overlapping faces / edges

The Fixes:

The 2nd image uses the Mesh boolean node with Union. (Doesn't always work)

The 3rd image uses an "inverse mold node" (works but some large meshes have problems)

Answer 3

So to summarize everything that was said and what I've found, for future noob comers here as I am, here is the answer I find the fullest:

Var. A. For very simple situation the easiest built-in tool is just use Select -> Select all by trait -> Interior faces

And then delete those faces.

Unfortunately, that does not solve the situation for anything else than a very simple geometry case.

Var. B. For many cases there is another way, that is also very simple. Thanks to james_t for pointing to this method. I think it is the best middle ground here:

1. First in edit mode select all with A

2. Check that options Auto Merge and Split Edges are both active and you have a least some understanding how they work so you've set the right Threshold depending on your object's mesh and its dimensions.

   Now press G and move it all a bit so that auto-merge kicks in. The best way to keep the object in place is the following sequence: G, Right, Left, Enter

   But you can do this even by mouse if placement is not of any importance to you.

   Now you've prepared the mesh for next step the best way you could.

3. Press the / to isolate the object for everything else.

   Disable the option "Toggle X-ray" if active.

   Deselect everything ALT + A.

   Now select all the external faces by any tool you find best. I prefer "Select box" tool. Just few Shift + LMB + rotating.

   And finally, invert selection Select -> Invert or CTRL+I. You should have all the internals selected. Delete all the selected faces.

   This should do the trick, but you may be left with some faces that are still partly inside, because the Auto-merge option, unfortunately, is not perfect. Though you can fix this by merging few vertices manually, if not many.

   While it is a long explanation, it is a very simple method. Just wanted to make it clear to newcomers.

Var. C. If you have a very complex mesh and the above-mentioned simple solutions do not suit you, you are left only with more complex non-integrated solutions. And here you should definitely check the idea by Rick T with geometry nodes.

While it is a complex thing to do yourself on a noob level, Rick T has done all the job for you.

So, you only need to import object from blend file to yours and copy modifiers CTRL + L from his object to yours.

You can edit the nodes in Geometry nodes editor, to suite your case. Afterwards, apply the modifier and delete everything that you do not need anymore. Read his answer for more info.

PS: I think that there should be a simple integrated solution for such clean-ups in blender. Especially, considering that it is so popular now for 3D printers, and all that nonmanifold internal faces are a huge pain for this job. And I hope it will be added in future.

PPS: There may be other solutions, and some for more limited situations. Check answer by james_t for example.