Polycarbonate Machining: Cutting, Drilling, Bending & Forming

Polycarbonate machines readily with standard woodworking and metalworking equipment, but a few critical parameters separate clean, crack-free results from chipped edges and stress fractures. The most common errors are using a dull or incorrect drill geometry (causing exit cracking), applying too much heat during cutting (melting at the kerf), and failing to pre-dry sheet before thermoforming (producing silver bubble streaks). Follow the parameters in this guide and you will get predictable, professional results from the first cut.

At a glance:

• Saw cutting: fine-tooth carbide blade (80T for circular saw), feed slowly to prevent heat buildup
• Router cutting: single-flute or O-flute upcut spiral, 18,000–22,000 RPM, 100–200 IPM
• Drilling: 60° included-angle point (flatter than standard metal drill), back workpiece, no coolant required for thin sheet
• Line bending: strip heater at 340°F, heat until material sags under its own weight, bend immediately
• Thermoforming: pre-dry 4–6 hr at 250°F, form at 340–375°F, use female molds for complex geometry
• Bonding: methylene chloride cement or two-part urethane; avoid acetone-based adhesives
• Edge polishing: wet sand to 2000 grit, then buffing compound; flame polishing causes crazing

Cutting Polycarbonate Sheet

Circular Saw

Use an 80+-tooth carbide blade for sheet under 0.250"; 60+ teeth for thicker plate. Triple-chip grind (TCG) or alternate top bevel (ATB) geometry produces cleaner edges. Set blade height no more than 0.25" above the workpiece.

Feed rate: 6–10 FPM for sheet up to 0.250"; reduce to 3–5 FPM for 0.500" plate. Too fast causes deflection and edge chips; too slow generates kerf heat that melts and re-fuses the PC. Keep the protective masking film on the sheet while cutting.

Router and CNC Router

Use single-flute or O-flute upcut spiral bits (solid carbide) for shaped parts and close-tolerance profiles — these geometries clear swarf without re-cutting melted material.

Air blast keeps the bit cool and clears chips. Avoid oil-based coolants — PC absorbs some oils, causing surface crazing.

Scoring and Snapping (Thin Sheet)

For 0.030"–0.060" sheet in straight cuts, score 3–4 times with a plastic-scoring knife or carbide scribe, then snap over a straight edge. The break is clean but slightly rough — sand to 220 grit to remove the sharp edge. This method is not suitable for thicker stock or for cuts within 2" of the sheet edge.

Drilling Polycarbonate

Drilling is the most failure-prone operation on polycarbonate. Standard twist drills with a 118° included-angle point generate excessive lateral force at breakthrough, causing a "blow-out" chip on the exit face — a star-shaped crack that ruins the part.

Correct Drill Geometry

Grind or purchase drill bits with a 60° included-angle point (very flat) for drilling plastics. This geometry reduces the axial thrust force during breakthrough and allows the chip to peel cleanly rather than fracture the substrate.

A brad-point (spur) bit is also effective — the center spur locates first while the outer spurs shear rather than push.

Never use step drills or spade bits without backing — these produce hoop stress at the perimeter that can initiate cracks days after drilling.

Drilling Parameters

Back the workpiece with scrap MDF flush to the exit face and clamp both together. A shifting backing still allows blow-out.

Countersinking and Counterboring

Use a 90°–100° countersink at 300–600 RPM with light feed; high speed melts and re-flows the walls. Run end mills at 800–1,500 RPM for counterbores with multiple light passes.

Fastener note: drill mounting holes 1/8"–3/16" oversize and use large washers to accommodate PC's high CTE. Avoid threading directly into PC — thread-root stress concentrations can initiate cracking under thermal cycling.

Line Bending

Line bending (strip bending) heats a narrow strip of PC along the desired bend line using a resistance strip heater. The material softens locally, is bent to angle, and is held in position while it cools — no oven required.

Strip Heater Setup

• Heater surface temperature: 340°F (170°C)
• Center the bend line on the heating element
• For sheet > 0.125", heat both sides to prevent whitening on the outer radius
• Heat time: 0.125" ≈ 45–60 sec; 0.250" ≈ 2–3 min per side; 0.375" ≈ 4–5 min per side
• Bend when the material sags slightly under its own weight; do not overheat or the surface blisters

Bend Radius Guidelines

Bending below the minimum radius causes surface whitening ("stress whitening") on the outer face — a cosmetic defect that appears as a milky zone along the bend. The part remains structural, but the clarity is compromised. For optical-quality bends, increase radius or use thermoforming.

Thermoforming

Thermoforming processes the entire sheet at elevated temperature, allowing complex three-dimensional shapes that line bending cannot produce.

Pre-Drying (Critical Step)

PC absorbs atmospheric moisture (~0.35% equilibrium). Undried sheet produces steam bubbles and silver streaks in thermoformed parts that cannot be removed. Pre-dry at 250°F in a convection oven: 4 hours for sheet ≤ 0.250"; 6–8 hours for thicker. Store dried sheet in sealed bags with desiccant if not forming immediately.

Forming Parameters

• Sheet forming temperature: 340–375°F (171–191°C)
• Mold temperature: 120–150°F (female); room temperature for drape forming
• Cooling in mold: minimum 2–3 minutes before demolding
• Draw ratio: up to 2:1; thinning and tearing above 3:1

PC's broad forming window (35°F range) makes it forgiving. Female molds produce sharper detail on the outer surface; male molds on the inner. Use 2–3° draft angles per face for easy demolding.

Bonding and Cementing

Solvent Cement

Methylene chloride (dichloromethane, MeCl₂) is the standard solvent cement for polycarbonate. It dissolves both surfaces slightly, intermingles the polymer chains, and on evaporation forms a molecular weld. Bond strength approaches 80% of the base material when properly applied.

Apply with a fine applicator tip, assemble within 30–60 seconds, clamp lightly, and cure 24 hours before loading. Do not use acetone, MEK, or cyanoacrylate on stressed PC parts — these cause stress crazing.

Structural Adhesives

Two-part urethane adhesives (Devcon Flexane, Loctite U-09FL) provide flexible structural bonds that accommodate PC's high CTE — preferred when bonding to aluminum channels or rubber gaskets. Epoxy creates a rigid bond; avoid in thermal-cycling applications.

Edge Polishing

Polycarbonate edges can be polished from a saw cut to optical clarity:

1. Never flame polish PC — torch heat causes surface crazing and residual stress. This is a common error; flame polishing is correct for acrylic but damages polycarbonate.
2. Sand progressively: 120 → 220 → 400 → 600 → 1000 → 2000 grit wet-dry paper
3. Apply Novus #3 then #2 with a soft cotton buff at 1,200–1,500 RPM
4. Final pass with Novus #1 for optical clarity

Routed edges start at 220–320 grit and require fewer steps.

Order Polycarbonate for Your Fabrication Project

For grade selection that affects machinability — particularly whether the part will be formed, bent, or bonded — review the polycarbonate grades guide before ordering. Abrasion-resistant (AR) coated grades cannot be thermoformed. If comparing PC fabrication difficulty to acrylic, see acrylic vs. polycarbonate or explore ABS machining characteristics as an alternative for enclosure applications.

More related guides

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Applications

• Machine Guards
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Industries

• Marine

Compare to other materials

• Ultem Vs. Polycarbonate
• Polycarbonate Vs. Acrylic
• Polycarbonate Vs. Abs

Frequently asked questions — Polycarbonate FAQ