Because microcontrollers are so cheap, plentiful, and versatile, electrical engineers tend to use them even when simpler integrated circuits or even discrete components could do the same job. Mechanical engineers often fall into a similar trap and use motors when they can achieve their goal using clever connections. Looking back, engineers didn’t have the luxury of taking these shortcuts, forcing them to come up with clever electromechanical solutions. Redditor DaveMakesStuffBC took a few lessons from history and applied them to this 3D printed mechanical 2D pen plotter.
This device does not contain any electronic components. It is purely mechanical, but is capable of drawing shapes such as stars and eights. The user spins a small wheel and the mechanism follows a preset path, moving a pen along the way. To change the shape, the user can swap the wheel. In theory, users could make as many wheels as they wanted. With enough of them, they could write the entire alphabet, every number, every punctuation mark, and even some of the most basic emojis. The size of the wheel limits the total length of all line segments in a shape, as well as their width and height, but alphanumeric characters are, by design, simple enough for this mechanism to handle.
The mechanism at the heart of this 3d printed The device follows the same principle as machining cams, which enabled automation before numerical control (NC) and then computer numerical control (CNC) came along. The wheel has two profiles projecting around its circumference, with the first controlling the X axis and the second controlling the Y axis. It’s a bit like the groove on a record player, but oriented so that it can guide both axes. An arm slides into the slot in the profile and holds the boom. It slides through a hole in a slider, which provides support in the Z axis and allows free movement in the X and Y axes.
The biggest challenge was translating a 2D shape into the rotated profile of the cam wheel. DaveMakesStuffBC did the CAD (computer-aided design) work in Onshape, but did not provide details on his methodology for generating the cam wheel geometry. One could do it through trial and error, but there are also a variety of more direct approaches. If you only want to print the parts that DaveMakesStuffBC already designed, they are available here.