Method for determining location of a lens machining tool in a turning machine configured for machining ophtalmic lenses

A method for determining a location of a lens machining tool in a turning machine configured to manufacture ophthalmic lenses, said location of said lens machining tool being defined according to at least two directions in said turning machine, said method comprising:

• manufacturing a calibration piece according to a predetermined theoretical geometry by using said lens machining tool;
• receiving data representative of geometrical characteristics of said calibration piece;
• and
• processing said data for determining the location of said lens machining tool relative to at least one of said two directions:
• wherein said lens machining tool has an offset location according to a first direction among said two directions, relative to a theoretical location, which is smaller than a first predetermined threshold,
• the manufacturing the calibration piece is configured to provide an at least partially annular groove in a main surface of said calibration piece, said at least partially annular groove being configured to form at least one sharp edge defining a slope discontinuity on said main surface,
• the receiving the data of geometrical characteristics of said calibration piece comprises measuring geometrical characteristics of said at least one sharp edge on said main surface, and
• said method further comprises deducing, from said measured data representative of geometrical characteristics of said at least one sharp edge on said main surface, a location of said lens machining tool according to a second direction among said two directions, the second direction being distinct from the first direction.