What is beveling on a lens?

Beveling creates a V-shaped ridge along the edge of a spectacle lens. This ridge seats into the groove inside a full-rim frame's eyewire, locking the lens securely in place. The bevel can be positioned at the center of the edge (standard), toward the front (front bevel), or toward the back (back bevel), depending on the prescription and cosmetic goals.

What is the difference between grooving and beveling?

Beveling creates a protruding V-shaped ridge on the lens edge that fits INTO the frame's eyewire groove. Grooving does the opposite: it cuts a channel INTO the lens edge that accepts a nylon cord. Beveling is for full-rim frames, while grooving is for semi-rimless frames. They are opposite approaches to lens retention.

Why do polycarbonate lenses chip during edging?

Polycarbonate is a softer, more flexible material that generates significant heat during edging. This heat can cause the material to soften, chip, or melt at the cut surface. Using slower edging speeds, appropriate diamond wheels, and water cooling reduces these issues. Some edgers have specific polycarbonate settings that optimize speed and pressure.

What happens if a lens is edged too tight for the frame?

A lens edged too large for the frame creates excessive pressure when inserted. This pressure can crack the lens (especially high-index or glass), warp the frame, stress the hinge mechanisms, and create optical distortion in the lens. The lens should fit with appropriate tension: snug enough to stay secure, but not so tight that it stresses either the lens or frame.

Edger Operation: Cutting and Shaping Spectacle Lenses for Frame Fitting

What Is an Edger?

An edger is the primary machine in an optical lab that cuts and shapes an uncut lens blank to fit a specific frame. Starting from a round lens blank, the edger removes excess material and creates the exact shape, edge profile, and finish needed for the chosen frame type. Modern edgers are computer-controlled, receiving frame shape data directly from a frame tracer.

Stages of Edging

Roughing

The roughing stage removes the majority of excess material quickly. A coarse abrasive wheel or diamond wheel grinds the lens blank down to approximately the final shape, leaving a small amount of material for the finishing stage. Speed is the priority here, not precision.

Finishing (Fining)

The finishing stage refines the lens edge to the exact size and shape specified by the frame tracer data. A finer abrasive wheel removes the remaining excess material with much greater precision than the roughing stage. After finishing, the lens should fit the frame with proper tension.

Beveling

Beveling creates a V-shaped ridge along the lens edge that seats into the groove (eyewire) of a full-rim frame. The bevel position, depth, and placement affect how the lens sits in the frame:

Standard bevel: Positioned at the center of the lens edge thickness. Works for most frames and prescriptions.
Front bevel: Shifted toward the front surface. Pushes the lens slightly backward in the frame, useful for reducing lens protrusion in plus prescriptions.
Back bevel: Shifted toward the back surface. Pushes the lens slightly forward, sometimes used for high-wrap sport frames.

For plus lenses with thick centers, a front bevel placement minimizes how much the front surface protrudes beyond the frame, improving cosmetic appearance. For high minus lenses, a standard or slightly back bevel may help conceal the thick edge behind the frame eyewire.

Grooving

Grooving is used for semi-rimless frames. Instead of a V-shaped bevel, the edger cuts a thin groove (channel) along the exposed edge of the lens. A nylon monofilament cord is then threaded through this groove to retain the lens in the frame. The groove depth and width must match the cord diameter for secure retention.

Drilling

For rimless (drill-mount) frames, the edger or a separate drilling unit creates holes at specific locations near the lens edge. The bridge and temples attach directly through these holes using screws or bushings. Hole placement must be precise to ensure proper alignment and minimize stress.

Safety Beveling

Safety beveling applies a slight rounding or flat to the sharp front and back edges of the finished lens. This prevents chipping during frame insertion and makes the glasses safer and more comfortable to handle.

Edging Stage	Purpose	Frame Type
Roughing	Remove bulk material quickly	All
Finishing	Refine to exact shape and size	All
Beveling	Create V-ridge for eyewire	Full-rim
Grooving	Cut channel for nylon cord	Semi-rimless
Drilling	Create mounting holes	Rimless
Safety bevel	Round sharp edges	All

Edger Types

Manual edgers: The operator controls the lens position and edging manually. Rarely used in modern practices but still found in some labs.
Semi-automatic edgers: The machine follows a pattern or template, but the operator manages setup and some controls.
Fully automatic (CNC) edgers: Computer-controlled from frame tracer data. The operator loads the blocked lens, and the edger completes all stages automatically. This is the standard in modern labs.

Edging too tight or too loose. A lens edged too small will not stay in the frame securely and may pop out. A lens edged too large creates excessive stress on the frame and lens, potentially cracking the lens or warping the frame. Proper frame tracer data and calibrated edger settings ensure the correct fit.

Material Considerations

Different lens materials require different edging parameters:

CR-39: Edges easily, produces a smooth finish. Standard settings work well.
Polycarbonate: Generates heat during edging that can cause chipping or melting. Requires slower speed and sometimes water cooling.
Trivex: Similar to polycarbonate but slightly easier to edge with less chipping.
High-index: More brittle than CR-39. Requires careful handling and appropriate edging speed to prevent fracturing.
Glass: Requires diamond wheels specifically designed for glass. Cannot be edged with standard abrasive wheels.

The quality of the edge directly affects lens durability, frame fit, and patient satisfaction. A well-edged lens fits securely in the frame without stress, has smooth edges without chips, and has the correct bevel or groove for the frame type. Edging is where precision manufacturing meets patient-facing quality.

Clinical Relevance

While many opticians do not operate edgers directly (the work is done by lab technicians or surfacing labs), understanding edger operation is essential for communicating with the lab, troubleshooting fitting issues, and knowing what to specify when placing lens orders. The ABO exam tests knowledge of the edging process and its stages.

Key Takeaways

Edging transforms a round lens blank into the exact shape for a specific frame
The main stages are roughing, finishing, beveling/grooving/drilling, and safety beveling
Beveling creates a V-ridge for full-rim frames; grooving creates a channel for semi-rimless
Bevel placement (front, center, back) affects how the lens sits in the frame cosmetically
Different lens materials require different edging speeds and techniques
Modern CNC edgers receive data directly from frame tracers for automated precision