In this work, a versatile and user-friendly selection of stereolithography (STL) files and computer-aided design (CAD) models are shared to assist educators and students in the production of simple and inexpensive 3D printed filter fluorometer instruments. These devices are effective resources for supporting active learners in the exploration of instrument design and performance. In contrast to sophisticated commercial-grade fluorometers, the models provided here are open source, customizable for a variety of applications, and easily assembled by students in activities that directly confront the "black box" perception of analytical instrumentation. In order to aid beginner CAD and 3D printer users, these models are compatible with accessible software packages, such as 123D Design and Inventor Professional. Additionally, CAD tutorials and extensive slicer settings are supplied to assist educators and students in modifying digital designs and obtaining reliable 3D prints. The provided filter fluorometer models are printed quickly, consume about a dollar's worth of plastic, and do not require complex support structures when 3D printed. Once fabricated and assembled, these devices perform well in a range of laboratory activities, including the quantitative determination of luminescent analytes at the ppm or ppb level.