What rotating machine did Leonardo da Vinci design to help polish concave mirrors?

Leonardo da Vinci designed a mirror-grinding machine to help polish concave mirrors.

His engineering notes include mechanisms for shaping and polishing optical surfaces. A concave mirror must be formed with a carefully controlled curvature, and Leonardo’s design used rotating motion and mechanical support to make the work more systematic than hand polishing alone.

The interest was connected with Renaissance optics and with Leonardo’s broader studies of light, vision, and perspective. Concave mirrors can collect and focus light, but their performance depends heavily on the accuracy of the surface.

Leonardo did not create modern precision optical manufacturing. His proposal was an early mechanical approach to a difficult craft process, and surviving drawings do not prove that the exact machine was built or used successfully in a workshop.