The IBM Selectric is one of the most recognized, popular, and successful typewriters series in history. At the same time, these machines represent a maintenance challenge due to their advanced mechanical system. Unlike other models, the writing element in an IBM Selectric is based on a sphere that changes position at an impressive speed, thanks to a complex digital-to-analog converter. Want to know how it works?
The IBM Selectric is on my list of pending subjects, but for space reasons (and the possibility of being kicked out of my house along with any new machine) I haven't acquired one yet. Several models can still be found in circulation, there is some availability of supplies, and documentation for maintaining these machines is easily downloaded from the Web. However, the IBM Selectric is much more than a solid typewriter. Many consider it an ancestor of early printers, and this is due to the presence of what could be interpreted as an early version of a digital-to-analog converter. Engineer Bill Hammack explains this in more depth in this video:
A distinctive feature of the IBM Selectric is its writing element, which at first glance resembles a golf ball. The American versions of the IBM Selectric can write an average of 88 characters, distributed in four rows and 22 columns. The converter manipulates two cables installed at the bottom of the machine, which in turn control the writing element, which rotates and tilts according to the pressed key. The movements and distribution of force in the cables are carried out through an ancient system called Whiffletree, which we can see frequently in windshield wipers. To specify each of the two bits required for tilting, the Whiffletree links move in blocks of just 0.06 inches, or 1.5 millimeters. The same principle is applied when rotating the element, only with much greater complexity due to its 22 positions.
Another aspect that Bill Hammack highlights at the end of the video is the possibility of connecting an IBM Selectric or another similar typewriter to a computer, turning it into a teletype, a classic communication device used in the past, when connection speeds were tiny and CRT monitors cost as much as a luxury item. The IBM Selectric is a true marvel of mechanics and engineering, which fortunately we can still appreciate.
