Cleaning up bad geometry
Now, the model should be watertight, but it is hardly clean and non-manifold. Now is the time to locate, identify, and fix the non-manifold points:
Clear the selected points (A).
Select all non-manifold points (Shift + Ctrl + Alt + M).
Unfortunately in sealing the edges, non-manifold geometry was accidently introduced into the model. All of the currently selected points represent a problem in the model that should be fixed.
The first step is to remove any points that are occupying the exact same spot:
Select all the points (A).
Click on the Remove Doubles button in the left-side bar.
When that is done clear the selection (A).
Select the non-manifold points again (Shift + Ctrl + Alt + M).
Choose one of the selected points and zoom in on it.
Deleting an extra edge
The previous screenshot is zoomed in on one such place. The darker grey areas indicate that there are multiple surfaces overlapping each other in that area, two faces on top of each other. There is some edge on the...
