3D Printing a Mechanical 2D Pen Plotter

Because microcontrollers are so cheap, plentiful, and versatile, electrical engineers tend to use them even when simpler ICs or even discrete components could do the same job. Mechanical engineers often fall into a similar trap and use motors when they could accomplish their goal using clever linkages. If we look to the past, engineers didn’t have the luxury of taking these shortcuts and that forced them to come up with ingenious electromechanical solutions. Redditor DaveMakesStuffBC took some lessons from history and applied them to this 3D-printed mechanical 2D pen plotter.

This device doesn’t contain any electronic components. It is purely mechanical, but is capable of drawing shapes like stars and figure eights. The user cranks a small wheel and the mechanism follows a preset path, moving a pen along the way. To change the shape, the user can swap out the wheel. Theoretically, users could fabricate as many wheels as they like. With enough of them, they could write out the entire alphabet, every number, every punctuation mark, and even quite a few of the more basic emojis. The size of the wheel limits the total length of all of a shape’s line segments, as well as its 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 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 projected around its circumference, with the first controlling the X axis and the second controlling the Y axis. It’s a bit like the groove in a record player, but oriented so that it can guide both axes. An arm rides in the profile groove and holds the pen. It slides through a hole in a slider, which provides support in the Z axis while allowing for free movement in the X and Y axes.

The biggest challenge was translating a 2D shape into the revolved profile of the cam wheel. DaveMakesStuffBC did the CAD (Computer-Aided Design) work in Onshape, but didn’t provide detail on his methodology for generating the cam wheel geometry. One could do so through trial and error, but there are also a variety of more direct approaches. If you just want to print the parts DaveMakesStuffBC already designed, they are available here.