CNC Machining Guide

Materials for CNC machining

Learn more about the most popular materials & finishes used in CNC machining.

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CNC Machining Guide

Materials for CNC machining

CNC machining can be used with a very wide range of engineering metals & plastics.

In this section, you will learn more about the key characteristics of the most popular materials. We will also examine the most common finishes that are applied to CNC machined parts.

Materials for CNC machining

Materials for CNC machining

Selecting the right material is a crucial step in the design process. The optimal material option is highly dependent on your specific use case and requirements.

Since almost every material with sufficient hardness can be machined, CNC offers a very large range of material options to choose from. For engineering applications, metals and plastics are most relevant and will be the focus of this section.

Surface finishes can also alter the properties of CNC machined parts and we will examine them below.

To get started, take a look at this decision tree. It contains high-level material recommendations that cover the most common design requirements.

Selecting the right CNC material chart

Metals

CNC machining is primarily used with metals and metal alloys. Metal can be used for both the manufacturing of custom one-off parts and prototypes and for low-to-medium batch production. Aluminum 6061 is by far the most used material in CNC machining.

Aluminum

Aluminum alloys have an excellent strength-to-weight ratio, a high thermal and electrical conductivity and natural protection against corrosion.

6061  7075  6082  5083 

CNC machining in Aluminum

Stainless steel

Stainless steel alloys have high strength, high ductility, excellent wear and corrosion resistance. They can be welded, machined and polished.

304  316  2205  17-4  303  420 

CNC machining in Stainless steel

Alloy steel

General use steel alloys with improved hardness, toughness, fatigue and wear resistance over mild steels, but low chemical resistance.

4140  4340 

CNC machining in Alloy steel

Mild steel

Low-cost, general use alloys with good mechanical properties, machinability and weldability.

1018  1045  A36 

CNC machining in Mild steel

Tool steel

Exceptionally high hardness, stiffness, abrasion and thermal resistance. They are used for dies, stamps, molds and other industrial tooling.

D2  A2  O1  S7 

CNC machining in Tool steel

Brass

Excellent machinability and frictional characteristics. Aesthetically pleasing golden appearance.

C360 

CNC machining in Brass

Plastics

Plastics are lightweight materials with a wide range of physical properties. They are often used for their chemical resistance and electrical insulation properties. Plastics are commonly CNC machined for prototyping purposes prior to Injection Molding.

ABS

Common, lightweight thermoplastic materials with good mechanical properties and excellent impact strength.

ABS 

CNC machining in ABS

Polycarbonate (PC)

Excellent impact strength, thermal resistance and toughness. Can be colored or transparent. Suitable for outdoor applications.

PC 

CNC machining in Polycarbonate

Nylon

General purpose engineering thermoplastic with all-around good mechanical properties and excellent chemical resistance.

Nylon 6  Nylon PA 6 GF30 

CNC machining in Nylon

POM (Delrin)

Easiest-to-machine engineering thermoplastic with high stiffness, excellent frictional characteristics and good thermal stability.

Delrin 

CNC machining in POM (Delrin)

PEEK

High-performance engineering thermoplastic used in the most demanding applications.

PEEK 

CNC machining in PEEK

Surface finishes

Surface finishes are applied after machining and can change the appearance, surface roughness, hardness and chemical resistance of the produced parts. Below is a quick summary of the most common finishes for CNC.

Surface finishes - As-machined

As-machined

As-machined parts have the tightest tolerances, as no extra operations are performed on them. Marks following the path of the cutting tool are visible though.

The standard surface roughness of as-machined parts is 3.2 μm (125 μin) and can be reduced to down to 0.4 μm (16 μin) with further operations.

Extra cost: None

  Tightest dimensional tolerances.
  Visible tool marks.
  No added cost (standard finish).
Surface finishes - Bead blasting

Bead blasting

Bead blasting adds a uniform matte or satin surface finish on a machined part, removing all tool marks.

Bead blasting is mainly used for aesthetic purposes, as the resulting surface roughness is not guaranteed. Critical surfaces or features (like holes) can be masked to avoid any dimensional change.

Extra cost: $

  Visually pleasing matte or satin finish.
  Will affect critical dimensions and surface roughness.
  Low-cost surface finish.
  Available in different coarseness.
Surface finishes - Anodizing (clear or colored)

Anodizing (clear or colored)

Anodizing adds a thin, hard, non-conductive ceramic coating on the surface of aluminum parts, increasing their corrosion and wear resistance.

Critical areas can be masked to retain their tight tolerances. Anodized parts can be dyed producing a smooth aesthetically pleasing surface.

Cost: $$

  Durable, visually pleasing coating.
  More brittle than powder coating.
  Can be applied to internal cavities.
  Only compatible with aluminum and titanium.
  Can be colored to any Pantone tone.
Surface finishes - Hardcoat anodizing

Hardcoat anodizing

Hardcoat anodizing produces a thicker, high-density ceramic coating that provides excellent corrosion and wear resistance.

Hardcoat anodizing is suitable for functional applications. The typical coating thickness is 50 μm and usually, no color is applied. Critical areas can be masked to retain their tight tolerances.

Cost: $$

  High wear resistance coating for top-end engineering applications.
  More brittle than powder coating.
  Can be applied to internal cavities.
  Only compatible with aluminum.
  Good dimensional control.
Surface finishes - Powder coating

Powder coating

Powder coating adds a thin layer of strong, wear and corrosion resistant protective polymer paint on the surface of a part.

It can be applied to parts of any material and is available in many colors.

Cost: $$

  Strong, wear and corrosion coating for functional applications.
  Cannot be applied to internal surfaces.
  Higher impact resistance than anodizing.
  Less dimensional control compared to anodizing.
  Compatible with all metal materials.
  Not suitable for small components.
Surface finishes - Silk screening

Silk screening

Silk screening is an inexpensive way to print text or logos on the surface of CNC machined parts for aesthetic purposes.

It can be used in addition to other finishes (for example, anodizing). The print can be applied only to the external surfaces of a part.

Cost: $$

  Low-cost printing of custom text or logos.
  Can be only applied to external flat surfaces of a part.
  Available in many colors.