3D printers

A FlexMendel 3D printer, operated by open-source software on an Arduino digital controller.
A FlexMendel 3D printer, operated by open-source software on an Arduino digital controller.

I’ve been working with 3D printers lately. Built one, in fact, during a workshop at Open Source Classroom. The printer is designed so you can see all its working parts, and I’ve been heartened by student and faculty interest in it. They’re fascinated to see a digital file, which has no mass or shape or form, be fed into a machine along with some plastic filament, and out comes a solid object you can look and hold and experience.

There’s a lot to say about the social and industrial impact of 3D printing, but my favorite questions are the ones on how it works. Because this is actually very familiar technology to all of us. We see it every time we hit “Print” on a report or picture.

Explaining the 3d printer

I started out explaining it this way: “It’s basically the same as an old-style dot-matrix printer, with one extra axis and substituting hot plastic for an impact print head.” After a few blank looks, I realized that most students had never seen a dot-matrix printer. Only older professors, who got their start printing mainframe jobs on a big dot-matrix line printer, could visualize what I was talking about.

(Excuse me, I’ll just be over in the corner here, feeling really old.)

Fortunately everyone today has seen an ink-jet printer, and the only difference between an inkjet and a dot-matrix is the type of print head. Inkjet printers move an ink-squirter over the paper. It goes side-to-side (the “X” axis) and top-to-bottom (the “Y” axis) to deposit an image. The printer is controlled by a built-in controller circuit, translating the image on your computer. Simple, right?

Back-of-envelope sketch of a 3D printer. Most of it is actually pretty old-fashion tech.
Back-of-envelope sketch of a basic 3D printer. Most of it is actually pretty old-fashion tech.

Now suppose you added a third axis; “Up and down”. Straight up, off the paper. Call that the “Z” axis, so you have an X, Y, and Z axis. And replace the ink squirter with a device that squeezes out hot plastic. Now you can not only print a pattern, but you can build up layers; that’s a 3D printer.

Layers on layers

“Print” a plastic circle for your first layer, and then another one on top of it, and one on top of that. Keep it up for 300 layers and you have a cylinder 12cm long. Change the pattern a bit from one layer to the next, and you can make “arbitrarily complex” shapes. Some of them, impossible by conventional machining methods.

Combining old tech with something really new

You could have built a 3D printer in 1970; all the components already existed. Step motors (that turn in discreet steps, instead of just spinning round and round)? Check. Precision machined rods and oil-soaked bronze bushings? Check. Control circuitry? Yep.  Meltable plastic? Sure. Computers and machine control language?  Um…

An arduino processor with some extra modules connected. The future is here, and it's not all that expensive.
An Arduino processor with some extra modules connected. The future is here, and it’s actually pretty cheap.

OK, all that stuff existed, but the price would have been way out of reach. Your descriptor file would have been encoded in a punched paper tape, or on punch cards, or on huge reels of magnetic tape. Your computer would have been the size of a refrigerator. You would have had to hire an engineer to do the translations and programming.

Today, think open-source software and an off-the-shelf Arduino processor you can hold in your hand. You’re talking less than $200 for a control circuit that would have required a Pentagon (or Bruce Wayne) budget just 45 years ago.

Hobbyists are building printers out of recycled parts, and with economies of scale, there are many complete models available for under $500. That’s the low end of 3D printing, but the technology is bustin’ out all over. There are 3D printers the size of houses, ones that use liquid polymers and UV lasers, and electron-beam printers that compose objects out of charged alloy molecules. The SpaceX corporation prints their Dragon rocket engines, and just delivered a printer to the International Space Station. (I suppose that makes sense: if you need a new part for something, and you’re in orbit, it’s a bit hard to just “Add to cart” on Amazon.)

But the biggest impact of 3D printers may be in the Third World. More on that, later.


Back when people used typewriters

Mark Twain was a famous early adopter of fancy technology, and he helped to popularize the typewriter. Isaac Asimov, author of more than five hundred books, had two IBM selectrics; if one broke, he shoved it aside and kept writing. It was a different time, when most information was distributed on dead trees. You know, right up until 22 years ago, before the World Wide Web.

Check out this video of kids reacting to a typewriter. Funny how a couple of them… want to keep it. It is sort of magical, letters appearing on the paper like that. The sound, the mechanism; this thing has authority.

I had a very difficult time with fine motor coordination* as a kid, and my handwriting was terrible. My sister taught me how to use a typewriter; home row, hands in position, strike the key – magic! A crisp letter on paper. I could get my thoughts out, finally.

I got very good at typing. In college, I made spending money typing papers for grad students who couldn’t spell. You kids, remember this: Spell Check won’t save you from using the correctly spelled wrong word. Homophones lurk, waiting to make you look like an idiot. But I will be sympathetic, pat you on the back and say; “There, they’re, their.”

Here’s what I like best about a manual typewriter: it has infinite patience. While you compose your next words (and you do compose, because it has no error correction), it waits, silent, wanting nothing. No electricity, no software patches, no pop-up ads. It offers no half-assed electronic opinions about your spelling or grammar. It has nothing else to do but wait for your next words. Now, that’s power.


  • Dave Hill compares his Smith Corona typewriter to a firearm… (Give me the typewriter any day.)
  • *Spinal meningitis, age 4. I was “lucky” but effects persist to this day. My handwriting has improved. The typewriter was a godsend.
  • Today I use a computer. My favorite is my Chromebook, which has a very long battery life, and no fan.
  • Next time you have some serious writing to do, instead of a word processor, try a code editor in “clean screen” mode. It’s the closest thing on a computer to using a typewriter. My favorite is Notepad++.

Something I learned from fixing things

Sewer Repair
Your savings? They are gone now.

Recently our sewer pipe broke, and it’s going to cost us 10 grand to fix it. Our yard is a mess with an excavation eight feet deep and 80 feet in length. But that isn’t the important thing.

The important thing is that in the last 5 years, most of the houses on the block have had to have this repair done. All the houses were built about 50 years ago. Buried clay tile only lasts about 40 to 60 years.

If you build a lot of something, they will all start to break at about the same time.

I’ve spent a lifetime fixing things. Cars, bicycles, photographic equipment, computers, and more. When something breaks, people turn around and look at me. From this I’ve learned that systems and objects have a “service life”. That is, you can expect them to last about n years before they need repair or replacement. If you have 100 of them, and plot how long they worked until failing, a failure curve will emerge.  Most of them will fail at approximately n years and a few will fail before and after.

The big picture

Crude MTBF concept sketch
Crude MTBF concept sketch (click to embiggen)

If you build a bunch of houses, most of them will need new sewer pipes around the same time. The same goes for roofs, furnaces, sinks, etc. Each of these systems has a Mean Time Between Failure (MTBF) curve. When you look at that curve, you know about how long it takes the system in question to wear out or at least need maintenance.

Ideally, you should use this information to plan ahead. Because fixing them is gonna be real expensive.

This also applies, broadly, to roads, bridges, tunnels, train tracks, schools, water mains and sewers, and much more. Now suppose you cut way back on maintenance and replacement? What would the result be?

Right: the roads, bridges, pipes, and whatnot will all start failing at once. It’ll be like an invasion, with foreign saboteurs dynamiting your vital infrastructure. Only in this case, the saboteur is named “Entropy” and you were supposed to be staying ahead of him all along. It is doubtful that actual terrorists could do as much damage on as wide a scale.

But maybe you were distracted by fighting wars you didn’t need to fight, propping up financial firms that were too big to fail, and just generally pretending that Entropy didn’t exist. Eventually you won’t be able to deny it anymore, and by that time the economy will be suffering because the infrastructure that supports it will be in shambles. It didn’t take much foresight to know Entropy was coming. All our experience in everyday life tells us about him.  Our leaders would be morons to pretend otherwise, and we’d be morons to keep voting for them.