# How a CNC Wood Cutter Works

How a CNC router turns a computer drawing and G\-code into motor moves that carve a star out of plywood\.

By bright\-dolphin\-6f01ce01

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/cBP9i9fNpwAj)

## Transcript

### 1. A machine that carves by numbers

This is a CNC router, a machine that cuts shapes out of wood\. CNC stands for Computer Numerical Control: a computer tells it exactly where to move, using numbers\. Drag to look all around the machine\.

Big workshop routers can hold a whole 4 by 8 foot sheet of plywood\.

### 2. Hold the wood still

First the wood is fastened down so it cannot slide\. Here, clamps press a sheet of plywood onto a flat board called the spoilboard\. The spoilboard is meant to get scratched, so the bit can cut right through the plywood without hurting the table\.

Many machines hold the sheet down with vacuum suction instead of clamps\.

### 3. A drawing becomes numbers

Someone draws a shape on a computer, like this star\. Software plans the route for the cutting tool and turns it into a list of commands called G\-code, such as: move to this point, at this speed\. The controller reads the list one line at a time\.

Every dot on the screen is a corner the bit must reach\.

### 4. Three ways to move

The bridge across the table, called the gantry, rolls front to back\. The carriage slides left and right along it, and the spindle moves up and down\. These three directions, called X, Y and Z, let the bit reach any spot over the wood\. Pick one to watch it move\.

### 5. Motors that move in tiny steps

Each direction has its own electric motor: the black boxes glowing now\. The controller sends them a fast stream of electrical pulses, and each pulse turns a motor by one tiny step\. Toothed racks and gears turn that turning into straight, precise sliding\.

Some machines use servo motors, which also check their own position as they move\.

### 6. The spinning bit

The spindle is a strong motor that spins the cutting bit very fast, often around 18,000 turns a minute\. The bit is not a saw blade\. Its sharp spiral edges shave tiny chips from the wood with their sides and tip\.

A common bit is a quarter of an inch wide, about 6 millimetres\.

### 7. Cut the star

Press Start cutting\. The bit spins up, dips into the plywood and follows the outline of the star\. It cuts in two shallow passes instead of one deep bite, which is gentler on the bit and leaves a cleaner edge\.

Shown about five times faster than real life\. A cut like this moves at roughly 2 metres per minute\.

### 8. Carved, not built

When the last pass breaks through, the star comes free\. A CNC router makes shapes by taking material away, the opposite of a 3D printer, which builds them up\. The same list of numbers can cut the same star again and again\.

Small tabs often hold a part in place until the cut ends; they are trimmed off by hand\.