Basic types of CNC routers

The CNC router you select will need to handle your workload and be an appropriate fit for your work environment. Two basic considerations are how many axes you need on your router, and what type of motors it will use.

How many axes do you need?
In general, there are four levels of CNC woodworking machines you can purchase depending on the number of axes needed to do the work you have in mind.

• 2-axis: These are low-end routers for hobbyists to create basic signs or household items. They don’t have a true Z axis, and they’re not intended for industrial use.
• 3-axis: The most common CNC routers, the standard 3-axis router features an eight-foot long X axis, a four-foot Y axis, and a six-inch Z axis.
• 4-axis: The addition of a fourth axis allows material to be rotated around the vertical axis or on a CNC lathe for architectural millwork or advanced artistic carvings.
• 5-axis: Offers two additional axes for rotating parts and cutting three-dimensional objects without having to reposition them. Can machine five sides of a cube at once.

The vast majority of small-to-medium businesses choose 3- or 4-axis models. Hobbyists can get by with small 2-axis routers, and 5-axis routers are primarily used for the boating, automobile, and aerospace industries.

Stepper motors vs. servo motors
You have two options for the motors that will power your router: stepper or servo.

A stepper motor moves in steps and keeps count of the steps to determine its position. This is an open loop control, meaning that after controller tells the motor to move a certain number of steps, it assumes that it’s done. You don’t get feedback letting you know where the motor is, and in complex designs, this can lead to errors.

Stepper motors have been around for a long time and are extremely reliable. They also require very little maintenance. However, they aren’t as accurate as servo motors. They are also quite noisy and there are limited sizes available.

Their performance also depends on speed. Stepper motors have high torque (the force that causes rotation) at low speeds, but may suffer from choppy performance. High speeds are smoother but don’t have as much torque.

Instead of counting steps, brushless servo motors send feedback to the computer to keep track of their position. This is a closed loop control: feedback from an encoder lets the motor automatically correct its location. By self-correcting, you get faster point-to-point speeds and increased power.

Servo motors are very accurate and smooth and the result is fine resolution of the finished product. However, they can be more expensive and are traditionally found only in high-end CNC woodworking machines. They require more maintenance in dusty environments, as the encoder is susceptible to dirt and vibration problems.

To maintain a servo motor’s accuracy, you must tune it so it responds the way you want. Tuning is not an easy process and requires a lot of knowledge about the technology, but you gain greater control over the motor’s behavior.