13 Parts of a CNC Machine — CNC Block Diagram
Learn more about the different parts of a CNC machine and their functions.
CNC (computer numerical control) machines are complex pieces of equipment designed to automatically manufacture parts from a wide range of materials that include metal, plastic, and wood. CNC machines come in many different configurations, but the most common are CNC mills and CNC lathes. CNC lathes are better suited to processing cylindrical parts whereas mills can be used on flat, curved, or angular parts.
This article will describe the different parts of a CNC machine. Some parts are common between lathes and mills, like the control unit, driving system, and feedback system, while others are specific to a certain type of machine. For example, tailstocks and headstocks are only found on CNC lathes.
1. Input Device
The “input device” for a CNC machine is the means by which CNC programs are loaded into the machine. This input device could be the keyboard (to directly input G-code commands), a USB flash drive (to transport a completed program from another computer), or wireless communication (if the program is to be downloaded from another computer using the local network).
2. Machine Control Unit (MCU)
The MCU (machine control unit) is the set of electronic hardware and software that reads the G-code supplied by the input device, and translates it into instructions that can be executed by the tool drivers to perform the desired machining actions. It is one of the most important CNC machine components. The MCU interprets the G-code coordinates into movements carried out by servo motors along the various machine axes. It also interprets information from feedback sensors to ensure that the tool is in the expected position after the movement is completed. The MCU also controls tool changers and coolant activation as specified by the G-code. A typical control unit is shown in Figure 1 below:
3. Machine Tools
"Machine tools" is the general term used to refer to any tool that may perform a process on a workpiece, usually cutting tools. Machine tools take on many forms depending on the type of CNC machine. CNC lathes use stationary tools and move the spinning raw material into the tool to make cuts. CNC mills move spinning tools into stationary material. However, more complex 5-axis machines can move both the tool and the workpiece, which makes it possible to create more complex features in the finished part. Machine tools are often kept in “tool libraries,” which are machine racks to store all the tools that may be required to machine a part. A tool changer automatically removes a tool from the spindle, places it in the tool library, and installs the next tool. A typical CNC mill machine tool is shown in Figure 2 below:
4. Driving System
The driving system refers to the motors that move the tool along the various machine axes. In the case of a standard CNC mill, the bed is moved horizontally along the x- and y-axes and the cutting tool is moved up and down along the z-axis. In a standard CNC lathe, the driving system moves the cutting tool co linearly with the axis of workpiece rotation. The cutting tool is moved into the outer diameter of the material along the rotational axis of the workpiece vs transverse to the rotational axis. The movement in a CNC machine is often controlled by servo motors, ball screws, and linear guides. Servos can precisely move the ball screw nut to position the various mechanical components such as the bed and the spindle. Linear guides ensure movement of the bed and spindle is precise, with as little play as possible.
5. Feedback System
Despite the precision of the driving system, it may still be necessary to have a closed-loop control system so that after the machine moves a mechanical component to a specific position, this position is verified and, if necessary, adjusted. The position can be measured by making use of a linear encoder or a rotary encoder attached to the servo motor.
Special probing tools are also used to not only zero the machine but to also measure the actual part during machining to potentially adjust machining parameters to meet dimensional requirements. A typical probing tool is shown in Figure 3 below:
6. Display Unit
The display unit is a screen that displays important information to the operator, some displays have large high-resolution screens that display a wealth of information whereas others have small low-resolution screens with only the bare necessities displayed. The display unit shows how the operator interacts with the various CNC machine functions, such as inputting G-code or changing machine settings. The display unit, as shown below, also shows the current machine operating status.
7. Bed
A CNC mill’s bed is where the raw material is mounted. Various work-holding jigs are used to secure the workpiece in place. The bed often has t-slots or holes to which the jigs can be attached. Conventional CNC machine beds only along the horizontal x- and y-axes, but more advanced 5-axis machines can include rotational motions along the x- and y-axes. Figure 5 below shows a part mounted to the bed of a CNC mill:
In a CNC lathe, the tool turret, and the tailstock are mounted to the bed, and the raw material is mounted to the chuck.
8. Headstock
The headstock is a section unique to a lathe that contains the main drive, bearings, and gears needed to rotate the chuck at the required speeds for machining. The headstock can be found on the left-hand side of a CNC lathe. The headstock is usually enclosed and is accessed via removable inspection panels.
9. Tailstock
The tailstock is a CNC lathe component that is used to axially support long, cylindrical workpieces on one side while the chuck supports the other side while also rotating the material. Without the tail stock, the forces created during cutting will cause the material to deflect away from the cutter. The raw material is centered on the tailstock quill which rotates freely in the tailstock. It is especially useful for cutting components like power screws or shafts. The tailstock can only move along the lathe z-axis to account for different raw material lengths.
10. Tailstock Quill
The tailstock quill is situated in the tailstock, the quill has a conical end that is collinear with the spindle and chuck axis. When machining a long shaft, a blind hole is often drilled into the center of the end of the workpiece so that the quill can be positioned into it for support. The quill has only a limited range of motion. The tailstock is moved close to the part, then the quill is actuated with pneumatic or hydraulic pressure to secure the raw material in place.
11. Footswitch or Pedal
Foot pedals are used to activate and deactivate the chuck and tailstock quill of a CNC lathe. Foot pedals help operators load blanks and unload completed parts from the machine. CNC mills do not typically have foot pedals as the parts are already supported on the bed and the operators do not need to have both hands free when loading and unloading raw material.
12. Chuck
The chuck is a lathe-specific part that is used to grip the raw material while it is being machined on a lathe. It is rotated at high speed by the spindle. A chuck typically has three or four pneumatically or hydraulically actuated grips. Three-jaw chuck grips are self-centering. All the grips move radially at the same time. The grips on four-jaw chucks can be individually adjusted, and are not self-centering. Four-jaw chucks are more accurate than the three-jaw type. They allow for eccentric cutting, as their position can be precisely controlled to account for any variation in the raw material. Figure 6 below shows a typical three-jaw chuck:
13. Control Panel
The control panel contains the input device, the display unit, the keyboard, and other control buttons to help operators interact with the CNC machine. The control panel is often attached to the CNC machine with an extendable arm that allows the operator to position the screen in a convenient location.
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