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PMMA (Acrylic)

PMMA, or acrylic, is a rigid, optically clear plastic used where transparency and a glass-like surface matter. At 1.18 g/cm3 with 70 MPa tensile strength but only 5 percent elongation, it is strong yet brittle. It machines and polishes to optical clarity but chips and crazes easily, so it rewards patient, low-stress processing.

How PMMA (Acrylic) machines

Acrylic machines at 3.5/5 but is notoriously brittle and prone to chipping and crazing. Use very sharp tools, slow feeds, climb milling, and shallow passes to avoid cracking edges and stress whitening. Heat buildup melts and gums the cut, so manage chip evacuation and avoid recutting. Annealing reduces internal stress that triggers crazing.

Manufacturing & processing

PMMA is CNC machined and laser cut from cast or extruded sheet, with cast grade machining and polishing better. It can be flame- or vapor-polished to optical clarity and solvent-bonded for clean joints. Anneal before and after machining and bonding to relieve stress and prevent later cracking around fasteners and holes.

Typical applications

Acrylic is used for clear guards, display cases, light pipes, lenses, signage, windows, and instrument covers where optical clarity and rigidity are needed. It edge-polishes to a glass-like finish and accepts solvent welding for transparent assemblies. Common in retail, lighting, and laboratory enclosures requiring see-through, scratch-buffable surfaces.

When to choose it

Choose acrylic when you need rigid optical clarity at low cost and can manage its brittleness. If impact resistance is critical, polycarbonate is far tougher though softer and pricier. Avoid acrylic for parts that flex, take impacts, or see solvents that craze it. Use it where clarity beats toughness.

Suitable surface finishes

Common finishes for PMMA (Acrylic): bead blasting, powder coating. Use the finish selector →

FAQ

What is crazing and how do I prevent it?
Crazing is a network of fine cracks that appears when stressed acrylic contacts solvents or sustains internal stress. Prevent it by annealing before and after machining, avoiding over-tightened fasteners, relieving holes, and keeping incompatible solvents and cleaners away from loaded surfaces and freshly cut edges.
Acrylic or polycarbonate for a clear part?
Acrylic is harder, more scratch-resistant, clearer, and cheaper, but brittle. Polycarbonate is far more impact-resistant and survives flex and abuse, but scratches easily and costs more. Choose acrylic for static clear guards and displays; choose polycarbonate where impact safety or flexing is the priority.
How do I get clean machined edges on acrylic?
Use very sharp single-flute or polished tools, slow feeds, shallow climb-milling passes, and good chip clearance to prevent melting and chipping. Avoid recutting chips. Flame or vapor polishing afterward restores optical clarity, and annealing relieves machining stress that would otherwise craze the edges later.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.