## 1 Introduction  
Open source three-dimensional (3-D) printing developed from the self-replicating rapid prototype (RepRep) project [1; 2; 3], has widened the doors for innovation and excellence in varied domains [4]. Combining 3-D printing with off the shelf and easily available electrical mechanisms has provided cost effective opportunities to design and build customized scientific equipment [5; 6]. This equipment ranges from an automatic feeder for animal experiments [7] and time-sorting pitfall traps for sampling arthropods [8], to electronics to provide big data like IoT meter devices for smart and energy-efficient buildings [9] and even entire smart cities [10]. Open hardware has also been developed for more conventional scientific tools in biology labs [11], optics labs [12], and even DNA nanotechnology labs, which can fabricate DNA-coated for up to 90% less than commercially offered tools [13]. This trend in cost savings from 90-99% is seen in a wide variety of open hardware tools for science and their outputs [5; 6; 11; 12]. Moreover, the open source design platform has provided the opportunity for distributed manufacturing [14; 15; 16; 17; 18]--specifically to download the designs and print them anywhere at any time, which can provide additional savings from avoided shipping costs as well as various taxes and tariffs. These savings are perhaps most stark when distributed manufacturing using 3-D printing (which enables material minimization coupled to free complexity) is tied to some form of automation. For example, radial stretching systems with force sensors [19] or a sample rotator mixer [20] can save hundreds of dollars per scientific tool, a mobile water quality testing platform [21] or a syringe pump [22] saves thousands per tool, and a robot-assisted mass spectrometry assay platform [23] and an automated peptide synthesizer [24] can save over $25,000. Scientists can now design, share and build on one another's work to develop advanced scientific tools [25], such as devices to enable digital microfluidics [26; 27], large stage probing [28], and microscopy [29]. These tools can all be easily maintained, modified, upgraded, or repaired because the full assembly instructions and bill of materials (BOM) are included.  
To continue this development of low-cost open hardware tools, this paper describes the development of a desktop nutating mixer, which provides a fixed 20\({}^{\circ}\) platform tilt angle for a gentle three-dimensional (gyrating) agitation of samples. Such devices agitate liquids for chemical or biological scientific procedures by repetitively moving the vessels holding the liquids. Although, open hardware methods to mix samples have been developed in the past (e.g., rotating mixing and shaking [20], orbital shaker [5; 6], as well as using a 3-D platform for stirring and custom shaking [30]), they were either too violent to ensure foam free mixing in tubes or too large for conventional portable use. Proprietary nutating mixers cost hundreds of dollars and lack the ability to either repair or upgrade with digital files, as well as to accommodate custom sample sizes and mixing velocities. These shortcomings are overcome here with the development of an open source nutating mixer, which can be fabricated with a conventional fused filament 3-D printer capable of printing both hard and flexible thermoplastics and off the shelf electrical components. This study describes how the system was designed and manufactured in way that is universally replicable. The operation of the mixer is tested, and the technical performance is compared to conventional systems and an economic comparison is made with the closest commercial alternatives. Finally, future work will be detailed to enhance the performance of the system.