MY previous table, Arrakis 2.0, has found a new home and that left me in need of a new coffee table. I could go out and buy something fashionable, but I liked having the sand table, so I designed a new one. When the old table was moving to its new home, I managed to break the glass top and had to replace it with a new piece, custom made to fit the oak frame, for $330. I wanted the new table to be a little smaller so it would take up a little less space in my living room and could be easily transported by fitting through doorways, and would use a glass top that would be fast, cheap, and easy to replace. A bit of research led me to 24 x 48" glass that's a common size for coffee tables and available cheaply (about $100 delivered from amazon). 

Structure

I made a support frame from blue anodized 2020 t-slot. 

The sandbox is made using black anodized 2040 v-slot with a 3/16" thick G10 board, covered with white fake leather cloth, fitted into the lower slots of that frame. The upper slots of the long pieces hold RGB LED strips. The sandbox sits on threaded pins in the corners of the support frame. The 2' x 4' glass top just sits on top of the sandbox. I put strips of EPDM rubber weather seal around the top of the sandbox to keep the dust in and spilled drinks out.

The mechanism frame is made from black anodized 2040 v-slot and drops into the support frame, resting on 3D printed spacers that center it in the frame.

All the t-slot and v-slot pieces were milled square and tapped, and screw directly to each other without any corner braces.

Mechanism

The mechanism is a stacked belt coreXY type driven by cheap, Chinese-made iHSV servomotors with 20 tooth pulleys. Belts are 6mm wide 2GT type commonly used in 3D printers. The motors are mounted on 3D printed mounts at one end of the mechanism frame with a twist in each belt so that the belt teeth touch only the drive pulleys, helping to keep noise down. The idler pulleys are made using stacked F625 bearings in 3D printed concave flanges that prevent the belts from squeaking. 

The Y axis (the long one) uses wheeled carriages that roll on the v-slot frame. The X axis is a 12mm linear guide with each end screwed to the wheeled carriages. 

The magnet is a 20 x 20mm cylindrical N52 neodymium type. The magnet carriage/belt clamps are 3D printed parts that screw onto the bearing block on the X axis linear guide. The belt clamps hold the ends of the belts with the teeth interdigitated in narrow slots that don't allow the ends to separate. There is a 3mm air gap between the magnet and the bottom of the sandbox.

Belts are tensioned by sliding the motor mounts along the slots in the frame.

Electronics

Power is provided by a 24V 350W Mean Well switcher. The controller is a Duet3D Duet2...