If you have a model created from several objects or meshes, first make sure that each individual mesh is manifold (water-tight). You can tell this by going into edit mode, pressing A (once if any vertices are selected or twice otherwise) to select none, then hit ctrl-alt-shift-M (on a Mac it's ctrl-opt-shift-M).Prepping Blender Files for 3D Printing (via Beyond the Beyond)Any vertices that get selected when you press that key combination are non-manifold vertices that have to be fixed. Often, fixing these is just a matter of creating new faces (F key) out of sets of 3 or 4 vertices. Sometimes these are stray vertices that are unattached to anything, or are attached to just one vertex by an edge. These can usually be deleted, unless they are intentional (such as those vertices uses to affect the shape while using a subsurf modifier), in which case you want to wait until after you've applied your modifier to delete them. Another possibility are vertices that are part of more than one overlapping faces...
Open the copy of the file, and select each object, one at a time. In object mode, apply all modifiers, then switch to Edit mode, hit A once or twice to select all vertices, then press ctrl-T to triangulate all faces. I don't know why, but Blender does a much better job with Boolean operations if the meshes are triangulated.
3D printer jargon in action
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This is not so much 3D printer jargon as just 3D jargon, plain and simple. Much of this could easily just be instructions for a polygonal/sub-d modeling app. Much of this could also be in the magazine rack in the bathroom at my house.
"Water-tight" originally comes from injection molding, and referred to a mold that didn't leak.
"Manifold" is a mathematical term, and refers to the surface that bounds a volume; a non-manifold mesh is one that can't actually be printed, since it doesn't describe a solid.
Manifold? Pah. I demand a printer that can give me a Klein bottle!
'Manifold' does not mean "bounds a volume". Indeed, many objects that don't enclose a volume are manifold.
For example, in 3d, a simple open plane with zero thickness is a perfect 2d manifold (like an open line is a 1d manifold).
These are not good for 3d printing, really. But then, being manifold is not the only property a mesh must exhibit to be usable as an input to a 3d printer (it must enclose a volume indeed, but a surface can enclose a volume and be non-manifold at the same time).
I urge interested peeps to read the wikipedia article on the term 'manifold' or head over to the mathworld one.
Btw, if you want to avoid issues with non-manifold topology, use a modeling app that guarantees manifold meshes.
An easy & fun to use one, even for kids, is Wings3d (http://www.wings3d.com/). Wings is FOSS too, comes pre-built for all major platforms and can export STL straight away (the format unfortunately used by most 3d printing services).
@danielcolascione: Trust me, you don't want one. Unclogging a jammed four-dimensional print head is a bitch.
"Trust me, you don't want one. Unclogging a jammed four-dimensional print head is a bitch."
Especially since you have to unclog it before it jams.
As a Shapeways and Blender user, I can attest to how useful this page actually is. But it's definitely hard to understand -- check their forums at any moment to see people having trouble uploading non-manifold meshes.
Oh man, I love you, BoingBoing. The first time I saw RepRap mentioned on here, it inspired me to build my own at school. Yesterday night I was clawing my eyes out over this EXACT issue, and now here are the answers. How did you know?
Sorry for the threadjack, but I finally had to mosey on over from Google Reader and ask, "Is the RSS feed for BBG now just a subset of the main BB one?"
I don't recall seeing anything mentioning a change, but I also don't remember seeing stuff lately that was on BBG but not BB. So, is it safe to remove BBG from my reader?
I'm not an expert, but yes. And yes.
What a surprise to find this in my RSS feed. I wrote this article. It began life as a forum posting I wrote on the Shapeways forums after struggling (over the course of several weeks) with trying to create a printable mesh. It's a frustrating process that is hard to find good information about, so once I came up with a process that worked, I thought I'd share what I had figured out with other Blender users who wanted to use Shapeways' printing services.
The Shapeways folks seem to have found it useful. They did a little editing, added the illustrations, and posted it (with my consent).
Not sure if I should be flattered or offended at having it help up as "jargonny", though...