Acrylic

A Beginner's Guide to CNC Machining Acrylic: Tips and Techniques

About Acrylic

Acrylic is a popular and versatile material that is commonly used in a wide range of applications. Acrylic, also known as polymethyl methacrylate (PMMA), is a thermoplastic material that is lightweight, strong, and durable. It is also known for its excellent optical clarity, making it an ideal choice for applications that require transparency.

Acrylic is easy to machine and can be CNC machined into a variety of shapes and sizes. It can also be easily polished, making it a popular choice for applications that require a high-gloss finish. In addition, acrylic is resistant to weathering, UV light, and chemicals, making it a suitable choice for outdoor applications.

One of the key advantages of acrylic is its affordability, making it a cost-effective alternative to other materials such as glass. Acrylic is also available in a wide range of colors and finishes, allowing designers and manufacturers to create custom parts that meet their specific requirements.

Overall, acrylic is an excellent choice of material for CNC machining due to its versatility, durability, and cost-effectiveness.

Subtypes

Acrylic

Acrylic is a strong material with many advantages over glass. Acrylic can be machined easily, while glass cannot. CNC machining acrylic is possible when the task involves complex geometry and high levels in optical clarity. Acrylic’s clarity is ideal for inspection windows and instrumentation covers.

Surface Finishes

Standard finish is the most common and basic type of finish for acrylic parts. This finish is achieved by CNC machining the part and leaving the surface as it is, without any additional processing or treatments. While this finish is cost-effective and easy to achieve, it can leave visible tool marks on the surface of the part, appearing as swirls. This may not be suitable for applications where a high-quality appearance is required.

Bead blasting is a method of finishing acrylic parts that involves propelling tiny glass beads at high velocity onto the surface of the part. This process creates a matte, frosted appearance that reduces the visibility of tool marks and gives the part a uniform finish. Bead blasting is an effective way to achieve a high-quality appearance while also improving the part’s durability and scratch resistance. However, the process can be time-consuming and more expensive than a standard finish.

Custom polishing is a more advanced method of finishing acrylic parts that involves using chemical processes or manual sanding to achieve a high level of clarity and transparency. This method is ideal for applications where optical clarity is critical, such as lenses or light diffusers. Custom polishing can significantly improve the surface quality of acrylic parts, but it is more expensive and time-consuming than the other two methods.

Design Tips

Avoid sharp corners and edges: Acrylic is a brittle material, so sharp corners and edges can easily crack or chip. To prevent this, it is best to use rounded corners and edges in your design.
Use draft angles: Adding draft angles to your design will make it easier to remove the part from the mold and will reduce the risk of damage to the part.
Consider the thickness of the material: Acrylic has a limited bending strength, so it is important to design the part with an appropriate thickness to ensure it can withstand the loads it will be subjected to.
Use radii on internal features: Acrylic is prone to stress cracking, so it is important to avoid sharp internal corners. Adding radii to internal features will help reduce stress concentrations.
Avoid overhangs: Acrylic has a low heat distortion temperature, so overhangs can be difficult to machine without warping or deforming the part. It is best to design the part with minimal overhangs or to use support structures.
Consider the transparency of the material: Acrylic is known for its optical clarity, so consider how the part will look when it is finished. Avoid adding features that will obscure the part’s transparency.
Choose the right surface finish: The surface finish of the part can have a significant impact on its appearance and performance. Choose the right surface finish for your application to achieve the desired aesthetic and functional properties.

FAQ

Can acrylic be CNC machined?

Yes, acrylic can be CNC machined. In fact, it is a popular material for CNC machining due to its versatility and ease of machining.

How do you cut acrylic with CNC?

To cut acrylic with CNC, a cutting tool such as an end mill or router bit is used to remove material from the acrylic sheet. The cutting tool is controlled by a computer program that specifies the desired shape and dimensions of the part.

What speed to cut acrylic on CNC?

The optimal cutting speed for acrylic on a CNC machine depends on various factors such as the type of cutting tool, the thickness of the acrylic sheet, and the desired quality of the cut. As a general guideline, a cutting speed of around 3000-6000 RPM is recommended for most acrylic materials.

What temp does acrylic get soft?

Acrylic begins to soften and deform at temperatures around 100-120°C (212-248°F). The exact temperature at which acrylic softens depends on the specific type and grade of acrylic material.

What is the best tool to cut acrylic with?

The best tool to cut acrylic depends on the specific application and the desired quality of the cut. End mills and router bits are commonly used to cut acrylic on a CNC machine, but laser cutting and sawing can also be used depending on the thickness and complexity of the part. Diamond-tipped cutting tools are often preferred for high-precision cuts and to minimize the risk of chipping or cracking the acrylic.