The surface finish is an integral part of the CNC machining process, as many applications require both aesthetic and functional design. In 2025, industrial designers will have the necessary tools and checks to ensure designs are functional and help the product to stand out from the crowd.
At MDA, we are quality-driven and ready to customize parts for various industries. Whether the client is looking to adhere to tight dimensional tolerances or requires additional corrosion, our surface finishes can produce what you need.
What are Surface Finishes?
Surface finish is a step-by-step process of coating and texturing the surface of a part after its machining. This process removes the tool marks, improving the appearance and characteristics of the product.
Some common types of surface finishes include:
- As-machined
- Bead blasting
- Wet sanding
- Fire polishing
- Vapor polishing
Let’s cover them in detail in the next section.
Common CNC Machining Surface Finishes
Here are some of the surface finishes for various materials. Each surface finish has its purpose; choose the one which suits your preference.
1. As-Machined
Many as-machined parts are moulded to already have a particular texture or finished appearance, and they are fresh off the line with only minor tool marks and an average surface roughness. The difference between the actual and ideal machining surface roughness of a component is known as its average roughness (Ra), and it can change based on the use case.
The tightest dimensional tolerances and consistency across several units are two advantages of an as-machined finish. As-machined finishes, which can support any material, are excellent for parts that require dimensional integrity and extremely tight tolerances rather than just aesthetics. Having obvious tool marks on your finished part without a protective coating is a drawback of this surface finish.
2. Bead Blasting
Bead blasting is a finishing method that uses a pressurized air gun to blast parts with tiny glass beads. This method primarily enhances appearance by producing a light-textured, matte or satin finish. It is a kind of primary finish that creates a smooth surface by mechanically changing or eliminating machining marks by removing extra material.
The consistent and textured finish of bead blasting is one of its benefits. It can, however, alter the critical dimensions of the surface and has little effect on tolerances. The outcomes aren’t always the same because it’s a manual procedure that can alter the air pressure and glass bead size.
3. Wet Sanding
Finishing plastic parts with wet sanding is the best way to get them ready for painting or clear-coat polishing. Water-soaked fine-grit silicon carbide sandpaper is used in the procedure, which is then gently sanded in circular motions. The parts can be finished with a smoother surface by switching from a moderate to a low-grit sandpaper.
To encourage shine and sheen, you can apply and buff a clear-coat polish that is safe for plastic once it is smooth.
4. Fire Polishing
While fire polishing isn’t suitable for all glass and plastic components, it’s a very efficient method of finishing CNC parts if the materials can tolerate the high temperatures. The part’s surface layer is melted by operators using an open flame, maintaining a precise temperature and angle throughout. The surface begins to tense and shift as it approaches a partial melting point, producing a polished, smooth surface.
Fire polishing can transform parts with a cloudy finish into a clear, flattened finish, depending on the material you’re finishing. Any ridges or bumps created during the production process are also lessened by fire polishing.
5. Vapor Polishing
Matte, opaque, or dull plastics can be clarified with a chemical vapour polishing technique, which leaves the finished product glossy and smooth. The polishing wheel can be used to enhance the natural properties of the material while smoothing out edges and irregularities. It may be necessary to sand CNC parts with obvious flaws before using vapour polish.
CNC Surface Finish Comparison Table
| Finish Type | Texture | Cost | Corrosion Resistance | Appearance |
| As-Machined | Visible tool marks | Low | Low | Basic |
| Bead Blasting | Matte | Medium | Medium | Good |
| Wet Sanding | Very smooth | Low | Low | Smooth matte finish |
| Fire Polishing | Ultra-Smooth | Low | Plastic only | High-Gloss |
| Vapor Polishing | Mirror-like smooth | High | Plastic only | Glass like clear finish |
Choose a Surface Finish That Matches Your Requirements and Application
It takes thought and assistance from the professionals to understand the surface finishes your parts need to look and work their best. MDA specializes in creating unique, personalized pieces that go above and beyond your expectations. We can make new or replacement custom parts for your applications with our unending attention to detail and timely deliveries.