A Drilled Rimless in a Plant Where Z87.1 Is Mandatory

The two stated goals conflict. 1.74 is the highest-index organic material commonly available: maximum refractive index, but also the most brittle, notch-sensitive, and prone to cracking or crazing at drill holes and at the edge under stress. Drill mounting concentrates stress exactly where this material is weakest, and his environment adds solvents, particulates, and repeated handling. The 1.74 choice is being driven by cosmetics while the actual constraints are impact protection and durability.

Options and reasoning:

• Polycarbonate: impact resistant and inexpensive, drills acceptably, but soft (scratches), attacked by many solvents, and prone to stress cracking around drilled holes and near the AR coating edge. Poor Abbe value is a secondary concern at this power.
• Trivex: the best compromise here - good impact performance, drills and edges cleanly, better chemical resistance and coating adhesion than polycarbonate, at the cost of index 1.53 and somewhat thicker edges.
• 1.67: a middle path that drills better than 1.74, but it still lacks the impact pedigree the job requires.

Bigger judgement: his employer mandates Z87.1 protection on the floor, and a three-piece rimless mount with no side coverage is a poor way to meet that requirement. Recommend a Z87.1-rated full frame with side shields, plano through-power lenses in the appropriate material, and treat a rimless pair as his off-floor glasses if he wants them cosmetically. Safety compliance outranks edge thinness.

Decentration: frame geometric centre distance = 56 + 17 = 73 mm, half = 36.5 mm. His mono PD is 32.5 mm, so each lens must be decentred inward by 4 mm. Minimum blank size follows the usual relationship: blank = effective diameter + (2 × decentration), so a lens needing, say, a 58 mm effective diameter requires roughly a 66 mm blank. Larger blanks mean more peripheral thickness and more weight in a lens that is already carrying about 5.75 D of minus at the edge.

Drill-mount constraints to state on the order:

• Minimum edge thickness at the drill locations - typically about 2 mm is asked for, because the hole is a stress concentrator and thin stock cracks; a lens that ends up 1.2 mm at the temporal drill point will fail.
• Hole placement: keep the hole centres well inboard of the edge (several millimetres of material outboard of the hole) and avoid holes in the thinnest, highest-curvature region; supply the frame or a drill template so the lab drills to the actual mount geometry.
• With this power, the temporal edge is thickest (it is farthest from the optical centre), which is where rimless mounts usually show their weakness.

Judgement: if the order proceeds, Trivex with a properly sized, smaller eye shape - not 1.74 - and the lab should confirm feasibility of the drill geometry before surfacing rather than after.

Be explicit that rimless is a maintenance commitment, not just a look:

• Cleaning: microfibre and lens spray only; paper towels and shirttail wiping grind dust and grit into the coating and are a leading cause of AR failure and crazing. Give him a supply of cloths and a case he will actually carry.
• Solvents: tell him not to let hydraulic fluid or cleaning agents sit on the lenses; he should rinse with water and blot. Coated high-index and polycarbonate surfaces are the most vulnerable.
• Handling: demonstrate two-handed removal and show him how the exposed edges mean a drop lands on the lens edge - directly at the drill holes.
• Compliance: reiterate in writing that these are not Z87.1 eye protection and that he must wear the employer-issued protection on the floor; document that he was told.
• Breakage history: three pairs in two years argues for a spare pair and for checking what the warranty actually covers - drill-mount breakage at the holes is often excluded unless the mount and material were specified by the dispenser.
• Follow-up at one to two weeks to check for loose screws, cracked holes, and adaptation, since he is a first-time rimless wearer.