CNC milled plastic parts are very popular in the automotive industry, especially for automobile lighting.When making an outer lens cover, for example, a 3D printed SLA prototype only provides about 60% transparency when compared with a CNC machined PMMA prototype. Marks left by the printer can be a major problem, while SLA printing materials are not as effective as PMMA block.
Light guides are also suited to machining, since they require optical details such as prisms, teeth and other tiny shapes. 
CNC machining is widely used for small and medium-size high-strength components like pulleys, clamps and levers, which can be made from engineering plastics.
The process is particularly valuable for parts in custom machinery, where mass production using injection molding would be economically inefficient.
CNC machining is commonly used within the electronics industry to create plastic parts for goods such as semiconductors, IoT equipment and consumer electronics. Many electronic devices are contained within machined plastic enclosures, while CNC machining is also highly useful for the rapid prototyping of various electronic components.
CNC machining is frequently used to make plastic parts for the medical industry. These include medicine dispenser components, handles for surgical tools and components for electronic medical devices.
Consumer products, including household goods, appliances and even sporting goods and toys, are frequently made with CNC machined plastic components.
In addition to the prototyping of parts, CNC machining can be used to fabricate items such as custom models, enclosures, jigs and fixtures. 
