The Crank Box is a 3D printed project to download and print out on your own 3D printer. The simple model demonstrates pure mechanism is action. The handle drives a gear, which in turn dri as second gear and finally a crank and push rod. See the model in animated action here.
The joints are designed to be a tight fit. It should be possible to snap the models together without using any glue.
Once the parts are printed out, use this guide to assemble the model.