I would like to fill in the base of this geometry (red lines) so that it can be printed as a Vase. I thought the boolean operators would work but to no avail. Any tips?
First of all, you don't need that cylinder for the base, delete it. I suppose you wanted the height of the cylinder as the thickness of the vase bottom. The best thing to do with such a geometry will be the following:
Select the star object and press Tab to go into Edit Mode.
Select everything with A, then convert Tris to Quads with Alt+J. This is not necessary for 3D printing but makes the next steps easier.
- Deselect everything with Alt+A, then select the second row of vertices from the bottom on the inside of the object. You can do this by clicking between two vertices in a row and holding Alt. You have to repeat this on all sides, hold Alt+Shift while left-clicking to add selections.
- Now that you've selected the inner edge loop, press F to fill the hole with a new face.
- Next select the row of vertices below the new face. After selecting the complete edge loop, hit X > Delete > Vertices to delete the edge in order to delete the two bottom rows of faces.
- Now select the last bottom row of vertices on the inside. After the complete edge loop is selected, press F to fill the bottom with a new face.
- At last, check Face Orientation in the Overlays menu to see if the object shows completely blue faces. Also look inside the vase from the top. If there is anything showing up in red, select all with A, then press sHIFT+N to Recalculate Normals.