Acrylic Machining Guide — Saw, Router, Laser, Drill, Bend & Bond

Acrylic machines cleanly with sharp tooling but punishes dull blades with chipping, melting, and stress cracks. This guide covers the specific parameters for each major fabrication process: sawing, routing, laser cutting, drilling, edge finishing, strip-heater bending, and solvent bonding. Cast and extruded grades behave differently in several of these processes — the differences are called out where they matter.

At a glance:

• Saw or route with sharp carbide tooling; high RPM, steady feed rate
• Laser cutting: cast acrylic produces polished edges; extruded produces slight haze
• Drill with 60° included-angle (modified) bit or brad-point; back the workpiece
• Edge polish: scraping → sanding (180–1500 grit) → buffing or flame polish
• Strip-heater bending: heat to 290–340°F, bend gradually, hold until cool
• Solvent bond with Weld-On 3 (thin, capillary) or Weld-On 4 (thicker, gap-filling)
• Always leave protective masking on until fabrication is complete

General Machining Principles

Acrylic is an amorphous thermoplastic with a glass transition temperature of ~212°F (100°C). At that temperature it softens; below it, it machines like a brittle solid. The goals of every acrylic machining operation are:

1. Remove material fast enough that friction heat dissipates before the cut zone softens
2. Apply no point load at the cut breakthrough that would stress-crack the part
3. Never use dull tooling — dull tools rub rather than cut, generating heat and tearing the material

Leave the protective paper or film masking on both faces throughout all cutting, drilling, and routing operations. Remove it only after final assembly.

Sawing

Table Saw and Circular Saw

Use a fine-tooth carbide blade — 60–80 teeth for a 10″ blade. A triple-chip-grind (TCG) blade is preferred over alternating-bevel (ATB): it produces a cleaner edge with less chipping. Set blade height 1/4″–1/2″ above the sheet. Feed at a steady, unhurried rate — forcing the feed melts the kerf edges.

A table saw produces a sawn edge that is functional but not optically finished. Edge polishing is required if optical clarity at the edge is needed.

Band Saw

Use a skip-tooth blade (4–6 TPI) designed for plastics. Band sawing is used for curves and non-linear cuts. Feed slowly and evenly. Do not back up the cut with the blade engaged — this can stress-crack the acrylic.

Scoring and Snapping (Thin Sheet Only)

For sheet 0.093″–0.177″ thick, a plastic scoring tool can be used. Score with moderate pressure along a straightedge, then snap over a straight edge. Not suitable for precision cuts or for material thicker than 3/16″.

CNC Routing

CNC routing is the primary production process for shaped acrylic parts: display cases, letters, frames, and fixtures.

Bit Selection

• Single-flute (O-flute) upcut spiral — preferred for acrylic. Single flute means each flute carries more material per revolution, keeping the cutting zone cooler. The upcut geometry evacuates chips upward, away from the part.
• Diameter: 1/4″ for most work; 1/8″ for detail work. Avoid bits smaller than 1/8″ in acrylic — they deflect and heat excessively.
• Use carbide only. HSS dulls too quickly.

Parameters (General Starting Points)

If you see melting at the kerf, increase feed rate or reduce RPM. If you see chipping, slow the feed. Ramp into cuts rather than plunging — straight plunges can crack the panel or melt at entry.

Laser Cutting

Cast vs. Extruded Response

This is the most important grade-selection decision for laser fabricators. Cast acrylic vaporizes cleanly under the laser beam, leaving a polished, slightly glossy edge with no post-processing. This is equivalent to a flame-polished edge in optical quality.

Extruded acrylic has a lower molecular weight and different stress state. The laser still cuts it, but the edge shows slight hazing or micro-melting that is visible on clear transparent pieces. For opaque or colored acrylic signs where edge clarity doesn't matter, extruded is fine and costs less. For transparent or edge-lit designs, use cast.

Laser Parameters

Settings vary by machine type and wattage. These are representative starting ranges for a 60–150W CO₂ laser:

Air assist is mandatory for acrylic laser cutting — it prevents flame-back into the material and blows combustion gases out of the kerf. Without air assist, acrylic can ignite and flame.

Always use a working ventilation system. PMMA combustion gases include methyl methacrylate monomer — extract fumes from the work area.

Drilling

The Core Problem

Standard twist drills have a 118° or 135° included-angle point geometry. In metal, this works fine. In acrylic, the chisel edge of a standard twist drill applies a splitting force as it breaks through the back face — this is the primary cause of acrylic cracking at drilled holes.

Correct Drill Geometry

Use a 60° included-angle modified drill bit ("plastic drill" or "zero-rake drill") or a brad-point bit. Both shear rather than wedge the material. You can regrind a standard HSS bit to 60° if needed.

Drilling Parameters

• Speed: 500–1,500 RPM. Slower for larger diameters.
• Feed: moderate, never forced. Ease off near breakthrough.
• Backing: clamp sacrificial scrap under the drill-through point to prevent cracking on exit.
• Outdoor fastener holes: drill 1/16″–1/8″ oversized to allow thermal expansion movement.

Edge Finishing

Sawn or Routed Edge — Polishing Sequence

A saw-cut or routed edge can be brought to optical clarity:

1. Scrape with a cabinet scraper (optional, removes major marks)
2. Sand 180 grit — removes tool marks
3. Sand 320 → 600 grit
4. Wet sand 1500 grit — edge becomes semi-opaque
5. Polish with Novus Plastic Polish or plastic buffing compound on a muslin wheel

Do not use metal polishing rouge — too abrasive for acrylic.

Flame Polishing

A propane or hydrogen torch can be used to flame-polish an edge in 2–3 passes. The heat reflows the surface layer, producing a smooth, glossy finish quickly. Use for cast acrylic only — extruded acrylic flame-polishes less predictably due to higher internal stress.

Flame polishing introduces surface stress and slight distortion. Do not flame-polish edges of parts that will be solvent-bonded — the reflow creates a skin that inhibits solvent penetration.

Strip-Heater Bending

Strip heaters are used to make sharp-angle bends in acrylic sheet by heating locally along the bend line.

• Extruded: 290–320°F; bend when the material droops
• Cast: 310–340°F; 30–120 seconds depending on thickness
• Bend gradually; white stress marks mean you are forcing it
• Hold until the part cools below ~150°F before releasing

Minimum inside bend radius ≈ material thickness. Tighter radii cause crazing. For complex curves, oven-form over a mold.

Solvent Bonding

Weld-On 4 (IPS Weld-On)

Weld-On 4 is the standard solvent cement for acrylic. It is a methylene chloride-based cement that dissolves the acrylic surface, creating a molecular weld when the two surfaces are pressed together and the solvent evaporates.

Joint preparation:

1. Edges must be flat, smooth, and free of polishing compound (flame-polished edges are not suitable — re-sand).
2. Clean surfaces with isopropyl alcohol; allow to dry.
3. Apply Weld-On 4 with a needle applicator along the joint gap (capillary application).
4. Hold joint in position for 30–60 seconds; clamp lightly for 15 minutes.
5. Allow full cure for 24–48 hours before loading the joint.

Weld-On 3 is a thinner, faster-acting version for very tight joints. Weld-On 16 and 40 are thicker formulations with gap-filling properties, used when joint fit is imperfect.

Joint strength: A properly made Weld-On 4 joint on cast acrylic approaches the tensile strength of the base material (~10,000 psi). On extruded, joint strength is lower but adequate for most display applications.

For stock acrylic sheet and rod ready to cut, visit the acrylic line card.

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