CNC (Computer Numerical Control) machining is a subtractive manufacturing process that uses pre-programmed software and digital instructions to control and automate the movement of precision tools and machines. The process begins with a solid piece of material (called a billet or workpiece). Tools and drill bits cut away material selectively to create the desired part. Unlike additive manufacturing, which builds parts layer by layer, CNC machining removes material to achieve the final shape, making it ideal for high-precision metal and plastic components.

CNC prototyping uses computer-controlled machines to make precise prototypes from digital designs. These machines carve out shapes from materials like plastic, metal or wood based on the design. Starting with a digital model, the CNC machine follows exact instructions to create the prototype, ensuring high accuracy and intricate details. Unlike traditional prototyping methods, CNC rapid prototyping allows for iterations within days. This process speeds up product development by allowing quick testing and adjustments before making the final product. Industries like automotive, aerospace, medical and electronics use CNC prototyping to test concepts, refine designs and ensure quality before mass production. It’s a vital step that brings ideas to life, improving products and meeting high standards.

CNC parts can range from $1–$50 for simple components to several hundred dollars or even $1,000 or more for complex parts. Prices vary depending on part size, material, tolerance, complexity and machining time. Compared to additive manufacturing, CNC machining often allows for volume discounts on larger orders or multi-batch production.

The two primary CNC machining processes are CNC milling and CNC turning.

• CNC milling shapes parts out of a metal or plastic material blank that is usually flat, capable of holding dimensions to tolerances as tight as ±0.002” (±0.05 mm).
• CNC turning rotates the part when machining the desired shape, which results in cylindrical, conical and spherical parts.

At HLC, we also combine a range of other machining processes and tools to meet complex requirements, including:

• CNC EDM (electrical discharge machining) also known as spark machining, which uses thermal energy instead of mechanical force to remove material. It is ideal for producing precision dies and moulds and sharp internal corners or particularly deep cavity.
• CNC Boring which is used to enlarge or finish existing holes to highly precise dimensions.
• CNC Drilling complements milling and turning processes with precise drilling, countersinking and threading.

The aerospace, automotive, electronics, robotics and medical industries are among the largest users of CNC machining. Other industries that also heavily rely on CNC for high-precision and rapid parts and prototypes, include the oil and gas and consumer good sectors.

For features not otherwise specified, standard tolerances apply. These are industry-accepted allowable deviations from a nominal dimension. The standard machining tolerance is ISO 2768 Fine (F) for metals and Medium (M) for plastics. Tighter tolerances are then available on request. In this In-Depth CNC Machining Tolerance Guide, learn about different types of tolerances, the tightest tolerances achievable with CNC machining and how to correctly specify tolerances on your 2D drawings.

CNC machining is generally recommended over 3D printing when functional strength, production quality and material versatility are priorities. Machined parts are typically stronger, more precise, and offer a wider range of materials and surface finishes, making them ideal for rapid prototyping, end-use components and production parts. This is why CNC is typically used in the mid to late stages of development, when parts are ready to be tested for functional testing and validation.