3d Printing: Not for the Claustrophobic

When I was a kid, I loved exploring - climbing the big cypress near our house and finding paths to the top, or figuring out ways to reach the roof of our house. I even crawled under our house a couple times, and only once because my dad needed help getting the TV antenna wire under the house. That kind of fun stuff isn't just for kids. I remember when my aunt first started using a computer, she was playing a 3d game and managed to get into a place that was *just outside* the virtual world. Suddenly, she was seeing the back side of all the scenery and models, and could see how the scenery is constructed.

I'm getting to do that crawling around and exploring with 3d modeling too. SketchUp, my favorite tool for 3d modeling, started as an architectural sketching tool. Although it can do three-dee models, one weakness is that it doesn't always make perfect models suitable for printing. Most 3d printers expect the model to be watertight: no holes in the faces making up the model, or gaps between faces. Most 3d printers also expect that there's no hidden faces embedded inside the model. These two requirements are needed so the various algorithms for figuring out the 3d shape can figure out what counts as inside the model, and what counts as outside. One of the simplest ways to determine inside/outside is to draw a line through the model, and count the walls you encounter. If you find an odd number, then your end point is inside the model; even, and you're outside. Extra faces and holes mean the software loses track of the model shape, and you end up with a model with either odd faces, or even odder parts missing. SketchUp doesn't enforce either of those rules, and while there's software to check and fix models for you, it's a pain to have to use the external tools to do a sanity check after each bit of creative drawing.

That means my three-d modeling habit involves a lot of what I did as a kid: crawling around in strange places looking for signs of extra faces that should have been deleted. The picture at the top shows the 3d model of the telephone booth model in SketchUp. I've deleted the faces making up the bottom surface of the model, but you can see the outer wall, the hollow inner surface (light gray), as well as all the inner surfaces marking the limits of where the printing material goes (in light blue). On the left is the reverse image of the doorway; the four cylinders sticking out are actually the ventilation holes on the right side of the model. Although the original model only took about 90 minutes to draw, probably half that time was trying to fix faces that were either on the hollow inside, or were incorrect faces on the inside of the model.

So if you ask me what 3d printing means to me, it means an awful lot of crawling around in confined spaces. Good thing I'm not claustrophobic.