The Mechanical Glory of the IBM Selectric Typewriter

Computers & Mobile Robotics Science
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The word of the day is “whiffletree.”

Heck, that’s the word of the month, as far as I’m concerned.

A “whiffletree” is a mechanical digital-to-analog converter. Brilliant science-and-technology documentarian Bill Hammack, professor of Chemical and Biochemical Engineering at the University of Illinois, has produced this fascinating video anatomy of IBM’s classic Selectric typewriter, in which a 7-bit whiffletree is employed to convert keypresses (digital) to precisely coordinated tugs (analog) on the control cables that rotate and tilt the type ball. Doubly awesome is the fact that the video features an appendix (yes, a video appendix) which focuses exclusively on the whiffletree itself, closely illustrating its operation with a simple 2-bit case.

You may remember Bill, aka Engineer Guy, from the office copier anatomy video we hit last July. His videos should be held up as models of how to present complex technical information visually. [Thanks, Bill!]


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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

View more articles by Sean Michael Ragan


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