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Glass has long been a staple in products that require transparency, like displays and screens. In some cases, glass is irreplaceable. But in most, acrylic has taken over the industry due to its lower cost, similar transparency, and better impact resistance.
But how does it behave under machining? Is it hard to machine? This article sheds light on acrylic CNC machining, covering key properties, machining processes, and practical applications.
Why CNC Machine Acrylic?
Acrylic is an engineered plastic polymer, chemically known as polymethyl methacrylate (PMMA). It was introduced in the mid-twentieth century, as a light, more impact-resistant material. Since acrylic is a glass alternative, so its best characteristics are usually discussed in comparison to that of glass:
Transparency
Acrylic is highly transparent with a light transmission rate of about 92%. Its refractive index (1.49) is very close to that of glass (1.50), which makes it an excellent choice for optical clarity products like windows, and lenses.
Impact Impact Strength Strength
Ordinary glass shatters under stress but acrylic doesn’t. It can endure 17 times more impact load than glass.
UV Resistance
Unlike many plastics, which turn yellow when exposed to ultraviolet light over time, acrylic retains its clarity even after prolonged sun exposure. PLEXIGLAS® claims their casted acrylic won’t turn yellow for over 30 years.
Weight
Acrylic’s density is approximately 1.18 g/cm³, which makes it roughly half the weight of glass. The lightweight nature also facilitates easier handling during machining, transportation, and installation.
Chemical Resistance
Acrylic is resistant to multiple chemicals, including diluted acids, alcohols, and aliphatic hydrocarbons. So, it’s a suitable choice for laboratories and medical facilities.
Easy to Machine
Acrylic is an engineered plastic that has a consistent, grain-free structure. This uniformity makes it easier to machine into intricate shapes without the risk of splintering – a common issue with glass and other materials.
Best Acrylic for CNC Machining
Acrylics are primarily classified into two types based on how they are produced. We have cast acrylic and extruded acrylics. Chemically both are the same, but a different production method imparts different mechanical properties.
Cast vs Extruded Acrylic
Extruded acrylic is made through the extrusion process in which a volume of melted acrylic pellets is forced through a nozzle to form sheets with uniform thickness. It’s cheaper to make but the drawback is leftover stresses which make the material brittle. Moreover, extruded acrylic is anisotropic i.e. behaves differently in different cutting directions, making machining challenging.
In contrast, cast acrylic is made by pouring melted acrylic into molds, which are allowed to cool and harden. This process produces acrylic that is denser, stronger, and has isotropic properties i.e. same properties regardless of direction. This allows for easier machining.
CNC Machining Processes for Acrylic
To shape and profile the acrylic into a desired form, the acrylic often undergoes these machining processes:
CNC Milling
CNC milling removes material from acrylic sheets by feeding them into rotating cutting tools in the same direction as the tool’s rotation. This method is ideal for creating complex geometries, as well as performing shallow or deep cuts.
CNC Turning
In turning operation, the acrylic workpiece revolves while a single-point cutting tool removes the material. The cutting tool moves in a straight line along the perimeter of the workpiece to shape it as needed. Turning is for cylindrical parts and tasks like thread cutting, boring, and facing.
CNC Drilling
The process uses multi-point drill bits to form cylindrical holes by driving the drill bit perpendicularly through the acrylic sheet.
Laser Cutting and Engraving
It’s a non-contact process that employs a high-powered laser beam to cut and etch the acrylic with precision. This process is ideal for thin acrylic sheets which cannot handle the stresses of mechanical cutting tools.
Challenges in Acrylic CNC Machining
Plastics and polymers may not have the strength and hardness of metals but still, they pose other challenges.
Low Melting Temperature
Acrylic has a low melting point, between 140 to 160℃. So, friction during machining can cause it to melt, leading to rough surfaces, deformations, or tool clogging.
Cracking or Chipping
Acrylic is brittle, and if the cutting tools are not sharp or the cutting parameters are too aggressive, the material can crack, chip, or even shatter.
Surface Scratches
Acrylic is prone to scratching, so measures must be taken to avoid damage during handling and machining. Protective coatings or films are often used.
Surface Finishing Options for Acrylic
Acrylic is popular for its optical clarity and smoothness. But the machining process, may not turn it like that. So, post-machining, some finishing operations are carried out on it:
Vapor Polishing
Vapor polishing uses chemical vapors (methylene chloride) to smooth and polish the surface of machined acrylic. The vapors gently melt the outermost surface layer, leaving behind a glossy, optically clear finish. The method is popular for achieving a high transparency in acrylic.
Flame Polishing
In this method, the flame is directed at the edges or surface of the acrylic to melt and smooth the material. This process is quick and effective for removing machining marks and rough edges. Cast acrylic responds better than extruded acrylic, as the latter may develop cracks.
Buffing
Buffing is a mechanical process in which a soft cloth wheel, combined with polishing compounds, is used to smooth the surface. Buffing works well for larger, flat surfaces and is effective at removing minor scratches or blemishes.
Considerations When CNC Machining Acrylic
Whenever CNC machining acrylic, one has to keep in view these important aspects to minimize damage and get the best possible results.
Design Considerations
Machining kicks off with design. While designing an acrylic part, special care has been taken for wall thickness, tolerances, and undercuts.
For instance, the minimum wall thickness for machined acrylic should generally be around 0.5 mm. Anything thinner may lead to structural weaknesses. Similarly, the undercut’s depth should not exceed 10 times the diameter of the cutting tool.
Cutting Tools
Acrylic is a plastic polymer, much easier to machine than most metals in the industry, but still, you have to stick to the compatible tools. Using wood bits is never a good idea. Instead, carbide-tipped tools are recommended for machining acrylic due to their durability and resistance to abrasion.
The bit size also impacts the cut quality. In the case of acrylic, a larger bit can help remove chips more effectively. A 0.25-inch bit is usually recommended for general-purpose acrylic machining. Use a tool with few flutes (probably 1 flute) for effective chip evacuation.
Machining Parameters
Since acrylic can melt due to frictional heat, it’s important to balance the spindle speed and feed rate. As per experts, a spindle speed of 18,000 RPM combined with a feed rate between 100 to 300 IPM is best for most acrylic cutting operations.
Work Holding
Acrylic is a relatively soft material and can vibrate during cutting, making rough cuts if not secured properly. For best machining results, use robust clamping systems. To prevent acrylic scratching, place rubber pads in between.
For larger or more intricate parts, vacuum-hold systems are the preferred choice. To secure smaller delicate parts, we recommend using double-sided tape.
Applications of CNC Machined Acrylic
Acrylic has taken over most industries as a lightweight, and strong alternative to glass. Some common industries and their relevant applications are illustrated in the table:
| Industry | Applications |
| Electronics | – Protective housings – LED displays – Optical fibers – Control panels |
| Automotive | – Headlight covers – Tail lamps – Interior panels and dashboards – Instrument clusters |
| Medical | – Incubators – Lab equipment (e.g., centrifuge tubes, pipettes) – Dental devices – Protective shields |
| Construction | – Windows and skylights – Signage – Lighting fixtures – Sound barriers |
| Signage | – Custom-engraved signage – Displays – Trade show exhibits |
| Aerospace | – Aircraft windows – Canopies – Lightweight panels |
Choose Richconn for Acrylic CNC Machining Services
Are you operating in one of the industries mentioned above? Need a product or prototype that CNC machining acrylic? Richconn is ready to assist.
We have specialized machines, tools, and experienced technicians who understand the unique challenges of machining acrylic. With years of expertise, we deliver products crafted to precise shape and size standards.
Try Richconn’s Plastic CNC Machining Services today and bring your project to life with unmatched accuracy and quality.
