The Complete Guide to CNC Machining Acrylic Parts

Updated: December 04, 2023

Acrylic material is a transparent, rigid, thermoplastic substance frequently used in manufacturing. It has advantages over similar materials such as glass or polycarbonate. It’s also 100% recyclable. Yet, it’s truly important to know how to machine this material for the best outcomes.


Let’s learn how to properly machine acrylic sheets using a CNC router and other pieces of machinery. You will also discover how to avoid acrylic melting and how to choose the right cutter. 

1. Why Use CNC Machining to Cut Acrylic?

There are several manufacturing processes suitable for acrylic: CNC acrylic cutting, injection molding, acrylic extrusion, compounding, and acrylic welding. CNC machining appears to be a perfect solution for many applications, including cutting acrylic.


CNC machines are extremely precise. They can apply exactly the right amount of force to acrylic sheets to avoid damage or cracks. CNC units also produce components quickly and effectively, with accurate shapes and dimensions. This way, the waste is minimized, and the acrylic component life span is enhanced.


CNC machines are precise due to using multi-point cutting tools moving along different axes. It allows you to cut from different angles with uncompromised precision. After all, acrylic belongs to high-performance plastics with high impact resistance. The material can be effectively cut, at optimal handling strength, using CNC units.

Acrylic Parts from CNC machining

2. Tips to Get the Best Results from Machining CNC Acrylic

Here are some tips on how to approach the CNC cutting process done over acrylic:


2.1 Secure Your Material

Properly secure the acrylic polymer sheet on the worktable using clamps, wise, or other methods. Acrylic is prone to chatter, so you should ensure that there is no way workpiece vibration may arise during machining. Overuse, the quality of cutting and especially of surface finish may heavily deteriorate.


2.2. Use the Right Bits and Ramps

Ensure that you are machining acrylic with the right drill bit. Carbide is a great choice. Besides, many manufacturers prefer a 1/4-inch solid carbide O-flute designed for acrylic cutting and drilling specifically. You may also look for other options intended for acrylic cutting.


Make sure the bits are sharp since dull bits cannot create edges that are clean enough. Acrylic material is sensitive to worn tooling, and you may notice lots of imperfections on the workpieces if cutters are inadequate.


Another piece of advice is to use a ramp along with your bit. It significantly lowers the risk of a drill bit damaging the acrylic. Use a smooth ramp between 1 to 3 inches for the highest quality finish. 


2.3. Set the Right Feed Rate

Choosing the correct feed rate and speed rate is of equal importance. Higher feed will prevent acrylic from melting. But be careful since extreme external stresses may cause an acrylic component to break. Higher feeds can also disclose parts or leave blemishes. At the same time, slow feeds lead to unfinished surfaces. Take a couple of attempts to find an optimal setting.


2.4. Use the Correct Revolution Per Minute (RPM)

As for speed rates, you need to correlate them with your feed set. The type of acrylic you use will heavily impact the settings. Faster RPM, as a rule, requires an increase in the feed rate to prevent the melting of the material because of the increased friction impact. 


2.5. Set the Pass Depth at the Correct Inch

Cutting depth is another important consideration. For most materials, it should be half the diameter of the bit. Alternatively, some materials, including acrylic, may require a pass depth of 0.0625″ inches for optimal outcomes. Once again, you may need several tries to figure out the suitable value. 


2.6. Cut Direction is Important

The anticlockwise direction of cutting is hard to recommend. On the other hand, conventional or clockwise directions are known for producing the best outcomes. Just remember that they should be picked with the direction of the rotating cutter in mind. 

CNC Machining with Acrylic

3. How to Avoid Melting Acrylic During CNC Machining?

Arcylic melting occurs when the surface temperature breaches the melting point of the material. Here are some tips you can use to prevent acrylic melting:


  • Use a larger bit size. When cutting acrylic, it seems that large cutter sizes do a better job removing the plastic chips. They are capable of cutting the material off faster than the friction makes the workpiece melt. As a starting point, a 0.25-inch bit is suitable for most types of acrylic. Or just choose the largest size that corresponds to the component requirements. 


  • Cut at a steady rate. The common problem is that the inconstant rate leads to the occasional melting of the workpiece at certain points of the process. To prevent it from occurring, increase the IPM, so the cutter is not in contact longer than necessary. Can quickly but steadily, so you maintain control.


  • Keep the acrylic cool. If acrylic re-bonding is still the issue, consider putting acrylic in a freezer before cutting it. It’ll make the starting temperature lower. You may also use a cool mister on the plastic and blade on and off to reduce the temperature.


  • Use higher feeds. Once again, higher feeds help you cut through the plastic faster without compromising RPM much. It’s also helpful to control the temperature of acrylic workpieces.

4. How to Get Acrylic Smooth After CNC Routing?

A smooth finish can be achieved by using the ramp between 1 to 3 inches. It will help you to fixate the material at the desired angle, so it does not just plunge straight down. Besides, if the smoothness of the surfaces is crucial, consider increasing the speeds of cutting to the point that the material does not melt. It’ll help to achieve a higher finish grade.


Selecting the right tool is also the key. An upward spiral, single flute tool geometry typically gives the best results on acrylic. Consider using high-quality micrograin carbide with high-temperature resistance. together with upward geometry, you’ll achieve a smooth and consistent finish and the optimal chip evacuation.


Tool position is another aspect to pay attention to. Make sure that cutting flutes are not inside the collet. Just leave a small section of the shank exposed. besides, if the tooling is protruding too far, the material will show chatter and produce poor finish quality.

cnc prototyping

5. What Bit Do I Use for Cutting Acrylic on a CNC Machine?

A 1/4-inch solid carbide O-flute is greater for cutting because it has an up-store pulling out the plastic chips. It prevents chips from building up inside the curve of the cut. 


If you want to engrave acrylic, consider using a 60° engraving bit for V-carving. It comes with a flat-edge tip helping you achieve better edge quality compared to other bits. 


You should use bits designed specifically for acrylic or high-performance plastic. Ones that are intended for wood are not durable enough, while ones for metal put too much stress on acrylic materials. 


Take a look at what a solid carbide O-flute cutter looks like in the image below.

solid carbide O-flute cutter

6. Conclusion

If you intend to cut acrylic materials, consider using CNC machines such as lathes, routers, or mills. Choosing the correct cutter is also essential. If you experience issues with acrylic melting or cracking, adjust feeds and speeds of machining for better cutting and finishing outcomes.


Should you need high-end acrylic machining, contact ECOREPRAP with your project details. Get from us a free strategic session or a free quote, engineering assistance, and market-leading CNC service quality. Outsource your acrylic machining needs to a trusted provider. 

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