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The Basic and Types of Surface Finish for CNC Machining

Published on May 10 2022 by Alex Chang
The Basic and Types of Surface Finish for CNC Machining

The term "surface finish" essentially refers to the surface quality of a machined parts. A set of parameters is utilized for accurate computation of surface finish. Industries use a variety of procedures to alter or operate on a produced parts surface to achieve specific attributes. The last stage in the production schedule for the cnc manufacturing is often a post-processing phase, which should be finished and then moving to quality inspection before sending the end product to the customers.

What is surface finish

Surface Finish is a measurement of a surface's overall texture and is mainly based on three factors:

  • Lay: It informs about the surface pattern that is more prominent or frequent. The processing of the surface's manufacturing technique has an impact.

  • Surface Roughness: A measure of closely spaced surface irregularities is called surface roughness. When machinists talk about "surface finish," they typically mean surface roughness. They might refer to all three features collectively by using the phrase "Surface Texture," which is more appropriate.

  • Waviness: Surface Roughness focuses on more minor abnormalities, while Waviness refers to a broader range of possible irregularities.

Different types of surface finishing

Now that you are familiar with surface finish characteristics and pre-finishing preparation, it's time to discuss the many finishing alternatives for CNC components, including conversion coatings, plating, and abrasive and polishing techniques.

Black Oxide

The process of chemically turning a ferrous substance's top layer into black oxide is known as blackening. Fasteners treated with a black oxide coating may offer a light layer of corrosion and abrasion protection in addition to a good, clean black appearance. The black oxide may be waxed or oiled to provide an additional layer of defense to maximize corrosion resistance. Although it may dull the treatment's color, the wax coating offers incredible resilience. The process of black oxide treatment is often known as "gun bluing."

As machined

The strictest dimensional tolerances, up to 0.05 mm or greater, can be achieved by leaving a product with an as-machined finish. With CAM, or computer-assisted manufacturing, precise data pathways and tool paths that are true to the original design are possible. Standard finishes normally don't come at an extra expense. However, the pieces could appear dull and there will be obvious tool marks. Especially for prototypes, fixtures, and jigs, an as-machined product may be the most economical option without further surface finishing types.


An essential process in producing aluminum CNC machined components is anodizing. Anodizing is an electrochemical technique that adds an oxide surface layer to a metal object to give it better durability and a more appealing appearance. Although anodizing is often done on aluminum, it is possible to do it on titanium and magnesium substrates.

Anodizing comes in three main varieties: Type I, Type II, and Type III. Each one results in a distinct coating thickness and set of attributes since it is applied using a different method. Aluminum becomes electrically non-conductive and is protected from corrosion by anodizing.

Type I: The most straightforward kind, this one uses chromic acid to create a thin, ductile anodized coating on an aluminum component.

Type II: Type II uses sulfuric acid instead of chromic acid to provide a thicker anodized coating on an item, making it more suited for coloring.

Type III: The most popular form, hard sulfuric acid anodize, provides the most precise finish and can be utilized with a broad range of colors. But compared to Type II, this finish is slightly thicker (ranging from .001 to .004 inches). Type III and PTFE may also be blended (commonly known as Teflon). It produces a dry lubricating surface due to the PTFE.

Electroless Nickel Plating

This method deposits a nickel alloy coating using chemical reduction rather than an electric current. The greater phosphorus concentration of distinct layers, which enhances corrosion resistance but reduce hardness, is nickel-phosphorus. Additionally, if electroless nickel plating is used, it should only be done after heat treatment to maintain the corrosion-resistant qualities. Electroless nickel plating is an option for steel, aluminum, and stainless steel.


A chemical conversion coating called alodine is primarily used to shield metal against rust. It is mainly used to passivate aluminum since it protects the metal and acts as a foundation for paint coats. It doesn't harm metal, making it simpler to paint over it without causing any changes.

Alodine can be administered by brushing, dipping, or spraying. Because it can help heal a wide variety of minor defects from anodized surfaces, many people often mix it with Type II anodizing.

Powder Coating

Aluminum, stainless steel, and steel are all coated with powder, a process comparable to painting. This method involves electrostatically applying powdered paint to an item, curing it under UV light or in an oven at a temperature between 325 and 450 degrees. Powder coating produces a thick, homogeneous layer that is smooth and consistent in appearance, increasing longevity. It is available in several colors and gloss levels.

However, since powder coating can alter component dimensions, control of tolerance and roughness value is essential. Holes and mating surfaces with precise tolerances must also be prepared by masking. The electrical conductivity of powder coatings is also poor.


By using chemical reduction instead of the electric current required for electroplating techniques, electroless nickel plating (ENP) deposits a nickel-alloy layer. A nickel-phosphorus deposit with 2 to 14% phosphorus makes up the bulk of ENP used for engineering applications. The more the phosphorus level, the stronger the resistance to corrosion; nevertheless, a loss in hardness results from increasing phosphorus content. ENP provides a less expensive alternative to corrosion-resistant alloys for applications where wear and corrosion are issues. This is especially true when carbon steel has localized corrosion, flange attack, or weld corrosion.

Bead Blasting

Tiny spherical media are shot at the surface of a CNC-machined component during bead blasting. These media might be made of glass beads or other materials. Bead blasting often produces a consistently smooth surface with a matte or satin finish. This procedure uses tiny beads to remove material from the machined item's surface gradually. The post-process may therefore impact the part's dimensional correctness. But this could only have a very modest impact. Bead blasting is typically utilized in aesthetic settings and on goods requiring high visual standards.


The importance of surface finish in the final product presentation has been well shown in this article, and it is essential to keep it in mind and treat it with the most excellent care. The fundamental techniques for enhancing the surface finish of machined parts have been covered in detail. It is a vast field that requires careful study, and find the best approach for cnc manufacturing via research, and then go ahead with its implementation.

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