Like most furniture, a coffee table should both look good and function well. To function well, a coffee table just needs a flat surface. But looking good is a lot more complicated and depends entirely on owner taste. If kinetic art is your thing, then you might consider building this automatic sand art coffee table.
This is a coffee table with a large pocket in the center filled with sand. A ball bearing rolls around in the sand, leaving intricate patterns behind. LED lighting highlights those patterns and users can program their own sequences of movements to create whatever art they like.
The secret to a kinetic sand coffee table like this one is magnetism. There is a two-axis CNC system underneath the table with a strong magnet that pulls the ball bearing through the sand. In this case, the kinematics are straightforward with a linear rail gantry riding on a pair of linear rails. Stepper motors pull the gantry and carriage with GT2 belts.
An Arduino UNO Rev3 board controls those stepper motors through a CNC Shield V3 with two TMC2209 drivers. The sketch is very simple and doesn’t run G-code directly. Instead, the user must extract a series of coordinates from a G-code file and copy them into the sketch. But because this is a coffee table, most users will only need to do that one time to program a series of patterns to cycle through.
