“Hello. I’m the newest in design from Smith Corona!” This began the last dying breath of the sentient typewriter that Noah and I entirely dismembered. It’s last will and testament, provoked by hitting the demo button, is recorded here:
Sadly, although this fully working typewriter was begging to survive, we had no choice but to tear it limb from limb. Luckily for us, the newest in design was assembled entire in Phillips head screws, so there was little resistance. We took off the outer casing by unscrewing a bit, then pushing in a few latches. Inside, we found an electronic keyboard, a large circuit board, a mechanical carriage containing the ink stamper, and a large paper roller. We also found a label, which made us think that disassembly, at least to this stage, was meant to happen. The label described how to remove the ink cartridge, which we promptly did.
The ink cartridge was made almost entirely of cheap molded plastic, which makes sense since it would be cheaply made and thrown away. It included a plastic ribbon with coated ink, which is stamped onto the paper.
The next piece of interest was the keyboard, which also came apart easily. This “simple” component breaks down into 6 large pieces formed of rubber, plastic, and metal. The keys extend a metal spring element, press a contact through the rubber sheet, and connect the electrical contacts on the ribbon cable.
Finally, we came to the circuit board, a fascinating curiosity. The front side was riddled with components, each one precisely labeled on the board. Interestingly, the resistors and IC chips were all pin-through-hole, not surface mount, which brings an old-school charm to this board. The printed labels also give the impression that this was assembled by hand, another cool thing I wouldn’t expect if the typewriter wasn’t so old.
The carriage/ink/printing assembly was very complicated, so parts became increasingly hard to take apart. To briefly describe how it works, the carriage moves along the x axis by a linear rail, powered by a rack and pinion stepper motor assembly. There is another stepper motor that controls the y axis with a roller to move the paper. The plastic quality in this area was noticeably better, and more metal pieces were introduced. Interestingly, the gears remained plastic throughout. There must not be very much torque on them.
On the carriage itself, things become exponentially more interesting. I’ve attached a handy diagram to illustrate the process, but it’s still pretty hard to understand. Here, most pieces are metal or high quality plastic. In addition, there are no more Phillips heads. We were not meant to go this far.
- A solenoid activates, shooting the pillar straight up with the speed of a coursing river.
- The hammer, on a free-moving hinge, is displaced by the solenoid and rotates. The hammer has a spring which slowly accelerates it back to a resting position.
- The key ring rotates to move the correct key into place. While moving, the hammer pushes a single key, extending the living hinge spring element. The key stamp pushes through the ink ribbon and hits the paper, leaving a single letter.
- Limit switches on the sides of the carriage prevent it from careening off the edge of the linear rail.
After the complete disassembly, we filled out the sheets. There’s not much here that wasn’t discussed earlier in the blog, but here they are. The MVP tool is the Phillips screwdriver, and the MVP part is the living hinge letter stamp wheel, which is just really cool.
