Optical Glass

Optical glass fails differently from every other material on this site. A crack does not just spoil the edge — it changes how light travels through the part. Subsurface damage left by a scribe-and-break line, or by a waterjet’s garnet, can sit microns below a surface that looks perfect and still scatter light after polishing.

Why the usual methods struggle

• Scribe and break — fast and cheap on flat sheet, but it propagates a vent crack that reaches well below the visible edge. On prisms and windows that damage has to be ground out, which defeats the purpose.
• Waterjet — no thermal damage, but garnet embeds in the cut face and the taper on thick sections is significant. Cleaning the abrasive out of an optical surface is its own process.
• Abrasive saw — workable, but the blade loads and the coolant carries swarf across the polished face.
• Diamond wire — cuts by grinding with a narrow, controlled contact, leaves a shallow damage layer, and can follow a curved path that a blade cannot.

Wire selection for optical glass

Finer grit is not automatically better. A very fine wire that has to be pushed to keep up will generate a deeper damage layer than a medium grit running freely — the damage depth follows the force per particle, not the grit number alone.

Process conditions that matter more than the wire

Coolant cleanliness is the single biggest lever. One stray particle carried across a polished face during the cut becomes a scratch that has to be polished out, and on a large optic that can cost more than the part. Filter the coolant, and dedicate a machine or a tank to optical work if you can.

Keep wire tension steady and the feed low. Vibration is what produces chipped edges on brittle glass, and on a wire saw vibration usually comes from an unbalanced guide wheel or a worn bearing rather than from the cutting parameters.

What we would need to advise you

Glass type, part geometry, the surface finish you need before polishing, and the damage depth your polishing step can remove. With those four numbers we can tell you the wire, the grit and the expected damage layer, and whether wire cutting is actually the right process for that part.