Everything You Need to Know About Spraying for CNC Machining and Manufacturing

custom part with spraying surface finishes

Spraying is a process used in manufacturing and custom CNC machining service to apply a coating or finish to a surface. This technique involves using a spray gun or nozzle to atomize a liquid or powder material into small droplets or particles, which are then sprayed onto the surface.

Spraying is used for a wide range of applications, including applying paints, coatings, and protective finishes to surfaces, as well as depositing materials for additive manufacturing and 3D printing.

There are several different types of spraying techniques, including air spraying, airless spraying, electrostatic spraying, and high-volume low-pressure (HVLP) spraying. Each technique has its own advantages and disadvantages, and the choice of technique will depend on factors such as the type of material being sprayed, the desired finish, and the size and shape of the surface being coated.

Surface preparation is an important aspect of the spraying process, as any contaminants or imperfections on the surface can affect the quality of the finish. Surface preparation may involve cleaning, sanding, or using a primer or base coat to prepare the surface for the final coating.

Overall, spraying is a versatile and effective method for achieving a high-quality finish on a variety of surfaces, and it is a key part of the manufacturing and CNC machining process.

Pro & Cons


  1. Efficiency: Spraying can be a very efficient process, as it can cover large surface areas quickly and evenly.
  2. Versatility: Spraying can be used to apply a wide range of materials, including paints, coatings, and adhesives.
  3. Consistency: Spraying can produce a consistent finish, with minimal variations in thickness or texture.
  4. Precision: Spraying allows for precise control over the amount and direction of the material being applied, making it ideal for complex shapes and designs.
  5. Cost-effective: Spraying can be a cost-effective option for high-volume production runs.


  1. Overspray: Spraying can produce overspray, which is the unintentional deposition of material on surfaces other than the target surface.
  2. Safety concerns: Spraying can produce harmful fumes and require the use of personal protective equipment (PPE) to prevent inhalation and skin exposure.
  3. Environmental impact: Some spraying techniques can release volatile organic compounds (VOCs) into the environment, which can contribute to air pollution and other environmental issues.
  4. Surface preparation: Spraying requires careful surface preparation to ensure that the finish adheres properly and produces a high-quality result.
  5. Equipment costs: The equipment required for spraying can be expensive and require maintenance and repairs.

Design Tips

When designing a CNC machined part with a spraying surface finish in mind, there are several factors to consider:

  1. Material selection: The material being machined and the type of surface finish being applied should be compatible. Certain materials may require specific types of coatings or finishes for optimal performance, so it is important to choose materials and finishes that work well together.
  2. Surface finish requirements: The desired surface finish should be considered during the design process. The complexity of the part and the type of spraying technique used can affect the achievable finish quality.
  3. Surface preparation: The surface of the part should be properly prepared for spraying, which may involve sanding, cleaning, or applying a primer or base coat to ensure proper adhesion and a high-quality finish.
  4. Tolerances and dimensions: The part design should take into account the required tolerances and dimensions for the finished part, as well as any additional requirements for post-machining operations such as sanding or polishing.
  5. Accessibility: The part design should consider accessibility for the spraying process, including the ability to access all surfaces that require spraying and any masking or protection needed to avoid spraying unintended areas.
  6. Production volume: The production volume for the part should be considered, as certain spraying techniques may be better suited for high volume production runs, while others may be more appropriate for low-volume or custom work.


How long does spray paint last?

The longevity of spray paint depends on several factors, including the quality of the paint, the surface being painted, and the conditions the painted object is exposed to. Generally, spray paint can last for several years if it is applied properly and the object is not exposed to harsh weather conditions or frequent abrasion.

How long does spray finish take to dry?

The drying time for spray finish varies depending on the type of finish being used, as well as environmental factors such as temperature and humidity. Typically, spray finishes can take anywhere from a few minutes to several hours to dry completely. It is important to follow the manufacturer’s instructions for drying time and to avoid touching or handling the object until the finish is fully cured.

What to avoid when spray painting?

When spray painting, it is important to avoid the following:

  • Spraying in windy or dusty conditions, which can cause overspray and affect the quality of the finish.
  • Spraying too close to the surface, which can cause drips or pooling of paint.
  • Holding the spray can in one spot for too long, which can result in uneven coverage or a buildup of paint.
  • Touching or handling the painted surface too soon, which can smudge or ruin the finish.
  • Failing to wear appropriate personal protective equipment (PPE), such as a mask and gloves, to avoid inhaling harmful fumes or coming into contact with the paint.


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