This was a 3rd grade "Invention Convention" project. The goal was to make a low-cost durable rock tumbler using 3D printed parts. There are a number of parts included here and some additional materials required (motor, drive belt, plywood, machine screws and nuts, power supply, PVC pipe, 5/16-inch square steel, etc). Use this to print parts which can be used to put something like this together. The original design used a small DC geared motor which was too weak, and we switched to using a variable-speed drill motor (14.4V) with a rotary actuator for the speed control. Otherwise the amount of starting current is too great for a basic power supply. See assembly instructions for details on materials used.In addition to the planetary gear end bearings, we used inexpensive 5/16-inch square steel rod for the drive shaft (about USD $3.17 for a 10 food length at my local metal supply). We ended up taking apart an old variable-speed reversible drill and putting a drive pully in the chuck, and mounting the speed control to the inside of the box with a nautilus-shaped actuator. The rollers were 2 inch PVC with the spacer parts inside. The fit was tight enough that no ABS glue was needed. Everything went inside a box made of plywood. We used machine screws to hold the ends on so it could easily be taken apart for repairs and/or upgrades. The timing belt was a 13" timing belt purchased on Amazon. In retrospect a longer one would have been much better. The motor clamps were used to provide tension on the pulley.