Architectural Glass & Mirror CNC Vector Prepress Guide

1. The Brittle Fracture Mechanics of Glass Machining

Unlike ductile metals or plastics that shear into continuous chips, glass is an amorphous, brittle ceramic. Machining glass requires high-speed grinding with diamond-impregnated metallic and resin bond wheels under flooded water coolant to produce controlled micro-chipping rather than macroscopic catastrophic fracture.

Every interior sharp corner in a glass drawing is a severe stress concentrator ($K_t > 3.0$). If an unfilleted sharp corner undergoes thermal tempering in an oven at $620^\circ\text{C}$, the differential thermal expansion will instantly shatter the panel. Therefore, strict geometric vector rules govern glass CAM prepress.

2. Edge Profile Geometries & Diamond Tooling Sequences

CNC glass work utilizes 3 primary edge standards:

• Flat Edge with Arris (Ground/Polished): Flat central face flanked by two symmetrical $45^\circ$ arrisses ($1.0 - 1.5\text{ mm}$ wide) to remove fragile razor-sharp edges.
• Pencil Edge (Half-Round C-Shape): Continuous radius $R = T/2$, common on tabletop glass and decorative mirrors.
• Beveled Edge (Mitred): Angled front bevel ($10 - 35\text{ mm}$ wide) at $5^\circ - 15^\circ$ for luxury mirrors.

3. Critical Internal Corner Radius Constraints ($R_{\min}$)

Because peripheral grinding wheels have a finite physical diameter ($D_{\text{wheel}} = 80 - 150\text{ mm}$), a CNC router cannot machine an inside corner sharper than the tool's radius:

4. Vacuum Suction Pod Holding Margins & Safety Envelopes

Glass sheets are held rigidly on the CNC table solely by rubber vacuum pods. The high lateral grinding forces and pressurized coolant jet ($6 - 10\text{ bar}$) require robust clamping:

• Maintain at least $35 - 50\text{ mm}$ clearance between the outer glass cut path and the edge of any vacuum suction pod to prevent catastrophic wheel collision.
• Minimum surface area per vacuum pod: Ensure total vacuum clamping area $\ge 0.15\text{ m}^2$ per square meter of glass to resist lateral grinding torque.

5. DXF Prepress Formatting for Glass Processing Centers

Organize vector CAD drawings into distinct layers for automated CAM import:

• FINISHED_GLASS_OUTER (Cyan): 100% closed, tangent-continuous G02/G03 arc profile.
• CUTTING_TABLE_SCRIBE (Blue): Offset outward by $+1.5\text{ mm}$ per edge for the raw float glass score-and-snap table.
• HINGE_CUTOUTS (Green): Internal waterjet/drill cutouts for hardware mounting.
• SAFETY_LOGO_SANDBLAST (Yellow): Tempered glass certification stamp mark location.