Here’s a simple vibration table for making concrete tiles, made with a Black and Decker Mouse, some screws, nuts, washers, and compression springs, and scrap wood.
The springs I used are 1 3/4″, 1/2″ OD, .054WG, but any reasonable gauge should work. Tighten the screws to create a little compression. Use a pair of nuts on each screw to keep the nut from backing off under vibration.
I mix concrete to a “wet sand” texture and trowel into molds. The table helps create an even distribution with no voids and levels out the open surface of the mold.