Improve Precision & Surface Finish in Plastic Parts with Post-Machining Processes

CNC machining is an efficient and accurate way to mass produce plastic parts. For many applications, the surface finishes produced during machining are adequate for end users. However, others may require additional processing, including for uses that demand aesthetic appeal or extreme precision. To create these plastic part surface finishes, post-machining processes can be applied to produce your desired results.

Surface Finishing Process for CNC Machined Plastic Parts

Achieving the correct plastic part surface finish is critical for successful end-user operation. Rough or flawed finishes can lead to problems with visual appearance, overall functionality, and durability of the part. Various processes are available to produce different finishes, so be sure to select the best post-machining process for your goals.

If you aren’t sure which surface finish, process, or service is suitable for improving your CNC plastic parts, call 909-986-6565 to speak with an Upland Fab CNC machining expert.


Polishing is an efficient way to improve plastic part surface finishes. It can be accomplished through several methods, including:

  • Vibratory polishing, where plastic parts are put in a tumbler that uses rotation and vibration to deburr, eliminate tooling marks, and polish parts. This process is ideal for large quantities of plastic parts.
  • Bead blasting, where compressed air is blasted at the plastic part to remove abrasive material and tooling marks. It is ideal for achieving a matte or satin surface finish.
  • Filing, where edges and burrs are filed down on small, machined plastic parts. This process is generally used for low-volume productions.
  • Stoning, where stones and oil are used for deburring and removing sharp edges that could tear or snag during use.


While grinding is more commonly used for metal component surface finishing, it can also significantly improve and smooth plastic parts to produce precision surface finishes. Using slow-moving friction generated by an abrasive wheel, material is removed from a plastic part to smooth the surface.

A more precise version of grinding is lapping. Lapping also uses friction at a low speed to smooth a component’s finish, but instead of a wheel, it utilizes a liquid cutting tool (or Slurry) to produce precision results. It is ideal for any use requiring flatness, parallelism, and complete consistency on flat, concave, or convex surfaces.

Grinding and lapping both produce shiny CNC plastic part finishes.

Heat Treatment

Regardless of how fine the tooling is, all machining clouds the surface of clear plastic parts to some degree. For certain applications, such as when manufacturing a lens, this surface effect is unacceptable. Heat treatments and flame polishing can be used to eliminate this poor surface finish. A low amount of heat is used to flatten the surface and allow light to pass through the plastic part as designed instead of being dispersed and scattered by microscopic flaws in the material.

Cryogenic Deburring

Deburring is an essential part of preparing CNC plastic parts for industrial applications and end users. Cryogenic deburring is an exact and effective way to complete this post-machining process. Burrs are blasted from your plastic part using a liquid nitrogen in a controlled process. This service is faster, more efficient, and more cost effective than traditional manual deburring methods.

Upland Fab Provides Surfacing Finishing Services for CNC Plastic Parts

High-quality tooling and expert machinists will produce better surface finishes. That’s why your best option is to partner with an experienced machine shop with the equipment, expertise, and capabilities to complete any job on time and within your specifications. Upland Fab is here to help. We fabricate plastic parts with tight tolerances for high-performance assemblies and uses across industries. We are continually working to refine our precision services to increase the value and quality of your production.

Contact us to learn how our machining and post-machining services can enhance your operations. Request a quote to get started. We always provide quick quote turnarounds and will be in touch as soon as possible.

Precision Plastic and Composite CNC Machining

Precision Plastic and Composite
CNC Machining since 1970.

Precision Plastic and Composite CNC Machining
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