CNC Milling

Definition and Explanation of CNC Milling in Woodworking
Milling is a shaping, material-removal process and, along with sawing, planing, and drilling, is one of the most common methods used to manufacture wood products. CNC milling is used to create contours and free-form shapes with repeatable, computer-controlled precision. A distinction is made between 2D and 3D CNC milling.

In this article, you'll learn the most important information about CNC milling. You'll also find useful information about machinable materials and the applications of CNC milling in woodworking.

Milling on a CNC milling machine

Milling on a CNC milling machine

Table of Contents

Definition: What is CNC milling?

CNC milling involves machining millable materials using a CNC machine. “CNC” stands for “Computerized Numerical Control.” CNC milling is characterized by high efficiency and repeatable precision, as the milling process is controlled by a computer-based system.

Technical Fundamentals of CNC Milling in Woodworking

In woodworking, milling involves finishing edges, creating contours on panels, or shaping wooden blocks into any desired geometry. A CNC router performs these machining steps with repeatable precision, controlled by electronics and electromechanical feed mechanisms. This saves time and reduces the need for personnel. The mechanical feed also enables something that isn’t possible with manual feeding: simultaneous milling. The article “Counter-rotating Milling” explains why the direction is fixed when using manual feeding.

  • Edge finishing: A wooden panel or board is guided past a fixed milling head, the geometry of which determines the edge.
  • Contour Milling (2D): The milling cutter enters the panel at a specified depth and follows a preprogrammed contour.
  • Free-form milling (3D): In woodworking, this is primarily performed on four- and five-axis machining centers, where the spindle can also be swiveled and rotated. Robotic arms are mainly used when components are too large for a machining center, such as in timber construction.

Types of CNC Milling in Woodworking

Edge Finishing

Here, you guide a board or strip past a stationary milling head. The shape of the edge is determined by the geometry of the milling cutter.

CNC Face Milling

As an alternative to planing with a planer, the router passes over the surface in overlapping passes. The workpiece is then flipped over and routed again. This allows you to achieve a specific thickness or smooth out unusually wide pieces. Without a CNC machine, you can do this using a router and a face milling attachment.

Contour Milling

In 2D coordinate guidance, the milling cutter enters at the defined position and follows the desired contour. This allows for the precise milling of both external and internal contours.

Free-form milling

For complex 3D designs, the spindle of a multi-axis machining center traverses the surface in closely spaced paths. The precision of these paths determines the surface finish and machining time—and how much manual finishing will be required afterward.

Tip: The RUWI router table next to the CNC

Chamfering, slots, rounding, grinding, deburring, or face milling: For individual parts, rework, and anything else where programming isn’t worth the effort, the router table sits right next to the CNC machine. Multiple milling cutters can be clamped in at the same time—you simply go to the appropriate motor instead of tying up the CNC for the job.

What materials are used in CNC wood milling?

Generally, you'll be working with soft, machinable materials:

  • Various types of wood: hardwoods such as oak or beech, softwoods such as pine or spruce
  • Wood-based materials such as MDF, particleboard, multiplex, or plywood
  • Plastics such as Plexiglas or Makrolon, provided they do not contain any metallic inclusions
  • Fiber-reinforced composites such as GRP and CFRP: They are highly abrasive and require diamond-tipped tools as well as an extraction system designed to handle fine dust

Metals can only be machined to a limited extent on woodworking machines, as tool and machine wear would be too high.

Applications of CNC Wood Milling Machines

A CNC wood router is used to shape edges, panels, or blocks. Key examples:

  • Milling internal and external contours: 2D machines are cost-effective and precise for this task.
  • Nesting: All necessary components are cut from a single sheet in a single pass.
  • Drilling: Blind, through, and through-holes can be drilled automatically.
  • Free-form milling: 3D machining of complex shapes on multi-axis machines.

Free-form milling with flush trim bit

Free-form milling with the flush trim bit

Industries for CNC Milling

  • Carpenters and Joiners
  • Manufacturers of furniture, windows, doors, and wood components
  • Caravan and RV Interior Design
  • Boatbuilding
  • Model and Mold Making

The machine handles repeatability—but the result is determined beforehand: during the design phase, the selection of tools and clamping devices, and the feed rates and spindle speeds specified in the program. That is precisely where the expertise lies—expertise that a CNC machine cannot replace.

What kinds of workpieces can be made from wood using a CNC milling machine?

That depends on whether you're working with flat or block material. You process flat material, such as panels, on 2D milling machines; for "voluminous" components in all spatial directions, you use 3D milling machines.

  • Cabinet fronts and cabinet components
  • 3D Wooden Models
  • Countertops, Letters, Engravings
  • Front doors, interior doors, and cabinets
  • Stair treads, windows, fences

Post-processing on the RUWI router table after CNC machining

Post-processing on the RUWI router table after CNC machining

Requirements: Axes and Complexity

A 2D router machines panels but can also, to a limited extent, create deeper cuts such as blind holes. A machine with four or five axes can handle complex components because the spindle can also be swiveled. It’s important to keep in mind that wood expands and contracts. Changes in moisture content and dimensions between programming and assembly often exceed the machine’s precision.

Tool Changer

Automated tool changing reduces non-productive time. The CNC control system automatically determines when to replace milling cutters or drill bits. Common types include:

  • Pick-up changer (few tools)
  • Plate changer (medium capacity)
  • Chain Changer (Wide Selection of Tools)

Machine Tables

The machine table plays a key role in improving efficiency. Examples include:

  • Console tables with vacuum suction cups on sliding consoles
  • Grid or matrix tables with foam rubber seals and vacuum
  • Flat tables for 2D and 3D, often with clamping mechanisms

Advantages: Milling Wood with a CNC Router

  • Consistently accurate and precise, even for large production runs
  • High Level of Automation
  • Setup and programming time is required only once—it is not required for the second and all subsequent parts
  • Safety: The operator is separated from the milling cutter

Once programmed, the CNC milling machine repeats its movements exactly as programmed. What changes is the tool: its service life and sharpness determine at what point the hundredth part begins to look different from the first.

What types of machines are used for CNC wood milling?

  • CNC Machining Centers
  • CNC Gantry Milling Machines and Nesting Systems
  • Four- and five-axis machines for free-form designs

In addition, in woodworking, you'll find table routers, under-table routers, and stationary routers, though these aren't always CNC-controlled.

RUWI Woodworking Products

RUWI offers a variety of solutions for woodworking machinery. Whether you want to chamfer edges, slots, sand, or flush-mill: The RUWI router table complements a CNC system in situations where programming and clamping a single part aren’t cost-effective.

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