Creating new 3D printed objects by recombining models found in hobbyist repositories has been referred to as "re-mixing". In this paper, we explore how to best support users in remixing a specific class of 3D printed objects, namely those that perform mechanical functions. In our survey, we found that makers remix such machines by manually extracting parts from one parent model and combine it with parts from a different parent model. This approach often puts axles made by one maker into bearings made by another maker or combines a gear by one maker with a gear by a different maker. This approach is problem-atic, however, as parts from different makers tend to fit poorly, which results in long series of tweaks and test-prints until all parts finally work together. We address this with our interactive system grafter. Grafter does two things. First, grafter largely automates the process of extracting and recombining mechanical elements from 3D printed machines. Second, it enforces a more efficient approach to reuse: it prevents users from extracting indi-vidual parts, but instead affords extracting groups of me-chanical elements that already work together, such as axles and their bearings or pairs of gears. We call this mecha-nism-based remixing. In a final user study, all models that participants had remixed using grafter could be 3D printed without further tweaking and worked immediately.