# Blender 3D Printing hollow model

I am trying to export an .STL I can actually 3D print with Blender. I have run through all the tutorials, but my model won't print correctly. I believe the problem would be solved if I could just select the outer shell of the model.

I want to extract everything that is outside (the shell) and delete the inner core. After that I would like to close holes and simplify the model to print. How can I achieve this? Thank you for your help.

• If the outer part is not connected to the inner part, then you can select it by pressing L while hovering over it with the mouse. – gandalf3 Apr 10 '14 at 8:20
• Unfortunatley it is connect and rather complex as well. Therefore I am looking for a way to just get the outer shell (imagine a 3D skull without the inner complex part). Thanks for your help. – digit Apr 10 '14 at 8:33
• You could try addidng another mesh as hull and use several subsequent subsurf and shrinkwrap modifier to build a manifold hull. – user2859 Apr 10 '14 at 14:32
• Select the vertices around the part joining the inside and outside and hide them H, then you can use L to select the outer shell and hide it leaving the inside to edit or delete. – sambler Apr 10 '14 at 15:26
• You could also try creating a convex hull, by selecting everything in edit mode and typing Space > convex hull. – gandalf3 Jun 9 '14 at 22:51

If there is only one connection area between the inner and the outer shell:

• select a ring of edges/vertices around this connection
• press Ctrl + E and then click on "Select Loop Inner-Region".
• this will either select the inner shell or the outer shell. If it's the wrong one, press Ctrl + I (invert the selection)

If there are several, but not outrageously many holes between inner and outer shell:

• mark them as seams (Ctrl + E -> "Mark Seam")
• then press U -> Unwrap with everything selected to unwrap the model
• go into UV/Image Editor, select one of the vertices and press L to select one of the two shells, pull that away far enough so that it becomes easy to box-select
• Press "Keep UV and Edit mode mesh selection in sync"
• select one of the islands, it will select the corresponding mesh, too.

If there are outrageously many holes between inner and outer shell:

I don't know. You could try box-selecting the outside with "limit selection to visible" active, but you'll get a few inside faces, too. Some of them may disapper if you "Select less" a few times, and then not re-appear if you "Select more" the same amount of times.

You could try selecting the outer shell in Wireframe viewport shading just because it's further outside at the edge, rotating around your model.

• In Edit Mode, hit C and select everything you want to keep. Select inverse and H for Hide. This did the job for me. – digit Apr 8 '16 at 6:04

If I understand you correctly, Solidify modifier is what you are looking for. To test how it works try this:

• create a cube
• in the bottom left panel select Modifiers (the wrench icon)
• click add modifier, select Solidify (Generate colomn; when doing this, the cube should be selected), select params (thickness etc), click apply
• to check out how it worked, create another cube (preferrably bigger one), move it so that it intersects the first one, but doesn't cover it fully
• select the first cube, add Boolean modifier in the same fashion, use Difference (the left dropdown) with the second cube as Object (the right dropdown), Apply
• move the second cube away to see what is left from the first one. If you have done everything correctly, you'll see that the first cube (remainder) is hollow

In fact, this is possible for other objects, too (use the last 3 steps to check out how it works).

One thing that I can also suggest is to use the free plugin from 3YOURMIND (https://www.3yourmind.com/3d-print-add-on-blender) to export the model directly from Blender to their online platform. They then do free analyzation of the file, fix many of the most common formatting errors in the .stl for you and guarantee the printability of the final data in a variety of materials.

Several of the problems the other users mentioned (filling holes and gaps, creating clean connection points, etc) are completed as part of the analyzation process. It is definitely worth a try if it isn't working as a direct export from Blender.