Imagine that your ink-jet printer has gone wonky. It’s sitting on your desk, running its print head back and forth for hours, continually printing one word. Once the unruly piece of technology is under control, you manage to pull out the paper. You can see, and feel, that the word “ROTOR” has been built up from the paper’s surface. If you scrape it off, the word will sit on your desk, like a paperweight. That’s the essence of 3D printing.