What is Acrylic?

Acrylic is widely used in CNC machining applications because of its excellent optical properties and predictable machining behavior. Key characteristics include:

• Exceptional optical clarity
• Lightweight
• Excellent weather and UV resistance
• Good dimensional stability
• Good machinability
• High surface hardness
• Excellent surface finish capability
• Good electrical insulation
• Moderate chemical resistance
• Limited impact resistance compared to polycarbonate

Because acrylic is an amorphous thermoplastic, it offers consistent machining characteristics and does not exhibit significant shrinkage or warping associated with some semi-crystalline plastics.

Acrylic is a synthetic polymer produced through the polymerization of methyl methacrylate (MMA) monomer. The polymer structure provides:

• Excellent transparency
• Good UV stability
• Strong resistance to environmental weathering
• Good rigidity and surface hardness

Chemical Composition of Acrylic

Excellent Optical Clarity

Acrylic offers over 90% light transmission and exceptional clarity.

Superior Weather Resistance

Acrylic stays clear and attractive outdoors.

Good Surface Finish

Proper machining produces polished surfaces for displays and cosmetic parts.

Lightweight Alternative to Glass

Acrylic offers glass-like clarity at half the weight.

Easy Secondary Operations

Acrylic supports polishing, bonding, engraving, thermoforming, and painting.

Brittle Material Behavior

Acrylic is brittle and may crack under high impact.

Susceptibility to Cracking During Machining

Poor settings, dull tools, or excess heat can cause cracks and chips.

Limited Solvent Resistance

Many solvents can damage or crack acrylic.

Lower Temperature Resistance

Acrylic can soften under prolonged heat.

Poor Wear Resistance

Repeated abrasion can scratch acrylic.

Several acrylic grades are available depending on performance and manufacturing requirements.

• Cast Acrylic: preferred for machining, optical applications, and superior finish quality
• Extruded Acrylic: lower cost, consistent thickness, and commonly used for signage
• Impact-Modified Acrylic: improved toughness compared to standard grades
• UV-Filtering Acrylic: designed for museum, display, and specialty glazing applications
• Colored Acrylic: available in a wide range of translucent and opaque colors
• Optical-Grade Acrylic: manufactured for lenses, light guides, and precision optical components
• Cell-Cast Acrylic: premium grade offering enhanced clarity and machinability

Tooling

Use sharp, polished tooling specifically designed for plastics:

• Use polished O-flute or single-flute carbide end mills
• Use razor-sharp drills designed for acrylic or plastics
• Minimize tool runout to reduce chipping
• Use polished cutting edges to prevent material adhesion
• Avoid dull tools that generate excessive heat

The primary machining objective is to maintain a clean shearing action while minimizing friction and heat buildup.

Feeds, Speeds, and Chips

There is no universal cutting parameter because results depend on equipment rigidity, tooling, material thickness, and finish requirements. Use chip formation as the primary indicator:

• Produce continuous chips rather than fine powder
• Increase feed rates if material begins melting
• Reduce spindle speed when excessive heat develops
• Maintain consistent chip evacuation
• Avoid dwell marks and rubbing during finishing passes

Monitor part temperature, edge quality, and surface appearance throughout machining.

Cooling and Chip Evacuation

Use compressed air to remove chips and reduce heat accumulation.

• Keep chips clear of cutting edges
• Avoid recutting chips
• Verify chemical compatibility before using coolants
• Avoid aggressive solvents that may cause stress cracking

Workholding

Acrylic can be damaged by excessive clamping pressure:

• Use soft jaws or non-marring fixtures
• Distribute clamping forces evenly
• Support thin sections during machining
• Avoid excessive vacuum or clamp pressure
• Use protective masking when possible

When designing machined acrylic components, both material characteristics and manufacturing limitations should be considered.

Avoid Sharp Internal Corners

Sharp corners can concentrate stress and increase the likelihood of cracking.

Maintain Adequate Wall Thickness

Thin sections may chip, crack, or deform during machining and assembly.

Account for Thermal Expansion

Acrylic expands and contracts significantly more than metals and should be accommodated in assemblies.

Minimize Mechanical Stress

Avoid designs that introduce concentrated loads or high assembly stresses.

Consider Edge Finishing Requirements

Transparent components often require flame polishing, buffing, or vapor polishing to achieve desired optical quality.

Consider Operating Environment

Evaluate:

• UV exposure
• Temperature exposure
• Chemical compatibility
• Mechanical loading
• Optical requirements
• Long-term appearance expectations

For applications requiring greater impact resistance, materials such as polycarbonate may provide better performance.

Acrylic is frequently modified to improve performance in specialized applications. Common modifications include:

• Impact modifiers for improved toughness
• UV-filtering additives
• Anti-static coatings
• Abrasion-resistant hard coatings
• Optical enhancement additives
• Specialty color compounds
• Light-diffusing formulations
• Infrared-blocking additives

Material modifications may improve one property while reducing optical clarity, machinability, chemical resistance, or overall cost effectiveness.

Does acrylic machine well? 

Yes, acrylic machines exceptionally well when the right cutting tools and speeds are used.

What are common applications for acrylic?

Acrylic machined parts are best used for applications that require high optical clarity, UV resistance, and minimal load-bearing.

What tolerances can you hold when machining acrylic parts?

You can realistically achieve standards of ±0.004 in. to ±0.002 in.

Is Acrylic flexible? 

No, acrylic has low ductility, meaning it is a stiff, rigid plastic.