  Virtual Reality (VR) can support effective and scalable training of
psychomotor skills in manufacturing. However, many industry training modules
offer experiences that are close-ended and do not allow for human error. We aim
to address this gap in VR training tools for psychomotor skills training by
exploring an open-ended approach to the system design. We designed a VR
training simulation prototype to perform open-ended practice of drilling using
a 3-axis milling machine. The simulation employs near "end-to-end" instruction
through a safety module, a setup and drilling tutorial, open-ended practice
complete with warnings of mistakes and failures, and a function to assess the
geometries and locations of drilled holes against an engineering drawing. We
developed and conducted a user study within an undergraduate-level introductory
fabrication course to investigate the impact of open-ended VR practice on
learning outcomes. Study results reveal positive trends, with the VR group
successfully completing the machining task of drilling at a higher rate (75% vs
64%), with fewer mistakes (1.75 vs 2.14 score), and in less time (17.67 mins vs
21.57 mins) compared to the control group. We discuss our findings and
limitations and implications for the design of open-ended VR training systems
for learning psychomotor skills.
