  Manufacturing tools like 3D printers have become accessible to the wider
society, making the promise of digital fabrication for everyone seemingly
reachable. While the actual manufacturing process is largely automated today,
users still require knowledge of complex design applications to produce
ready-designed objects and adapt them to their needs or design new objects from
scratch. To lower the barrier to the design and customization of personalized
3D models, we explored novice mental models in voice-based 3D modeling by
conducting a high-fidelity Wizard of Oz study with 22 participants. We
performed a thematic analysis of the collected data to understand how the
mental model of novices translates into voice-based 3D modeling. We conclude
with design implications for voice assistants. For example, they have to: deal
with vague, incomplete and wrong commands; provide a set of straightforward
commands to shape simple and composite objects; and offer different strategies
to select 3D objects.
