Patent ID: 8919954

Claim:
A process for obtaining an ophthalmic lens, comprising: a step of providing a blank ( 16 ) made of a material able to be surfaced by machining; and a step of surfacing the face ( 17 ) of said blank ( 16 ) by machining, comprising, in succession, a step of machining a roughing surface ( 32 ), and a step of machining a finishing surface ( 20 ), said step of machining a roughing surface ( 32 ) being carried out with a machine ( 30 ) comprising a roughing tool ( 31 ) forming a roughing surface ( 32 ) comprising a roughing trough ( 33 ) having a circularly arcuate profile the radius of curvature (R′) of which is fixed by the shape of the roughing tool ( 31 ) and having a pitch (C′) defined by a roughing advance setpoint given to said machine; said step of machining a finishing surface ( 20 ) being carried out with a machine ( 30 ) comprising a finishing tool ( 10 ) that forms a finishing surface ( 20 ) by digging said roughing surface ( 32 ) to a depth defined by a finishing pass depth setpoint (A) given to said machine, thereby forming a finishing trough ( 18 ) having a pitch (C) defined by a finishing advance setpoint given to said machine; characterized in that: said step of providing a blank ( 16 ) comprises the step of selecting, for said blank ( 16 ), a said material that has a pitting appearance threshold during a said step of machining a finishing surface over a material removal depth (D) of 0.07 mm that is at least 15% higher than the pitting appearance threshold during a said step of machining a finishing surface over a material removal depth (D) of 0.22 mm, each said pitting appearance threshold being the finishing advance setpoint from which pitting appears for a preset material removal depth (D), each said material removal depth (D) being the sum of the finishing pass depth setpoint (A) employed and the roughing roughness B′ given by the relationship: B ′ = C ′2 8 ⁢ ⁢ R ′ where: C′ is the roughing advance or the pitch of the roughing trough; and R′ is the radius of curvature of the roughing tool or the roughing trough; said step of machining a finishing surface ( 20 ) comprises the step of selecting said finishing pass depth setpoint (A) between 0.015 mm and 0.075 mm; and said step of machining a finishing surface ( 20 ) comprises the step of selecting said finishing advance setpoint between 85 and 99% of the pitting appearance threshold for the material removal depth (D) given by the sum of the selected finishing pass depth setpoint (A) and the roughing roughness B′.