CNC Machining: An Overview
CNC machining is an efficient manufacturing process that removes material in a controlled manner to transform digital 3D designs into physical parts, typically made from plastic or metal. Many businesses rely on CNC machining services to produce parts and prototypes, with this versatile technology being used across various industries.
Despite all CNC machining technologies following a similar process—where software converts digital designs into machine instructions that direct the machine to cut material—the hardware and cutting methods can vary significantly between different types of machines.
In this article, we will compare and contrast two common CNC machines: CNC mills and CNC lathes. We'll explore their main features, key benefits, and the types of products businesses can create using each technique.
What Is CNC Milling?
CNC milling is a manufacturing process that uses computer software to automate and control milling equipment. It involves a variety of operations—such as face, angular, or plain milling—to produce precise components from suitable materials.
A CNC mill consists of a vertical spindle and a rotating head with a rotary cutter that feeds into the workpiece. During milling operations, the workpiece is securely held on the machine bed. The rotating multi-point cutting tools are then directed to the surface of the workpiece in a controlled pattern, gradually removing excess material until the desired shape is achieved.
CNC mills come in different configurations, including 3, 4, or 5-axis models. A typical 3-axis CNC mill moves the cutting tool in three directions—X, Y, and Z—while a 5-axis CNC mill allows the cutting tool to move in five different directions.
The greater the number of axes or cutting angles, the more freedom the machine has, enabling it to create complex components with intricate geometries and precise features. While 5-axis CNC milling offers superior versatility, it is more expensive, which can increase the cost of producing highly detailed and intricate parts.
What Is CNC Turning?
CNC turning is a widely used machining process that involves mounting materials in a rotating chuck while cutting tools are fed into the workpiece to remove material until the desired shape is achieved. This process is typically performed using CNC lathes or turning centers.
Before the advent of CNC technology, lathes were operated manually, making them labor-intensive. The introduction of Computer Numerical Control (CNC) technology has automated many of these processes through pre-programmed software, enabling more efficient operations on suitable workpieces. Common turning operations include drilling, boring, grooving, parting, facing, and knurling.
A CNC lathe consists of a chuck and various cutting tools. Before machining begins, the operator sets key parameters such as feed rate, cutter speed, and depth, which determine the cutting process. During turning operations, the chuck holds the workpiece in place while cutting tools, mounted on a turret, move toward the rotating workpiece to remove excess material as required.
Most CNC lathes are equipped with a single turret, applying individual cutting tools to complete various tasks on one side of the workpiece. However, in some cases, turning centers with both a main spindle and a sub-spindle are used for faster operations. In this setup, the main spindle initially machines the material, which is then transferred to the sub-spindle to complete operations on the opposite side of the component.
CNC Milling vs. CNC Turning: What Are Their Differences?
Features | CNC milling | CNC turning |
Main Operations | Plain milling, angular milling, and face milling | Taper threading external grooving, knurling, boring, threading, and drilling |
Suitable materials | Metal, wood, plastic, and composites | Plastic, wood or metal. |
Function mechanism | Tools rotate, part is fixed, or rotates in some cases | Rotating the part, with tools moving radially or axially along the part |
Shapes produced | Shapes that are both symmetrical and non-symmetrical. | Shapes like cones, cylinders, discs, polygons, and hexagons are created using axis symmetry. |
What Are the Advantages of CNC Milling?
CNC milling offers several advantages for manufacturers and prototyping companies. Unlike lathes, CNC mills are versatile machines capable of producing a wide variety of shapes. Additionally, different cutting tools can be used for processes such as roughing and end milling, providing flexibility for various applications.
Mills are also invaluable for post-machining, even though they are primarily production machines. They can be used to add intricate details to parts that have been turned, molded, or 3D-printed, enhancing their precision and features.
Another key benefit of CNC milling is its speed, repeatability, and cost-effectiveness in low-volume production, especially since it requires minimal tooling changes. This makes CNC milling a popular choice in both manufacturing and rapid prototyping services.
What Are the Advantages of CNC Turning?
The primary advantage of CNC turning is its ability to produce round profiles with high precision. Achieving accurate roundness with other CNC machining methods, such as milling or routing, is much more challenging.
CNC turning is also highly precise, making it ideal for boring holes with exact dimensions and tight tolerances. This precision is crucial in industries where accuracy is paramount.
In many cases, CNC milling and turning are used together to capitalize on the benefits of both techniques. Typically, CNC turning is performed first to create the basic shape, followed by milling to add more complex or asymmetrical details to the workpiece.
CNC Mill Vs. CNC Turning – Applications in Custom Part Fabrication
CNC mills and lathes are used in various machining processes across multiple industries, including electrical, woodworking, metalworking, automotive, medical, aerospace, and motorcycling. Below are some examples of parts produced using CNC milling and turning in custom part fabrication:
Examples of Parts Made with CNC Milling
1. Water Pumps: Multi-axis CNC milling machines can produce reliable impellers for hydraulic systems.
2. Enclosures and Housings: Custom-milled enclosures are used to protect internal components in electrical devices and other products.
3. Gears: Straight and spiral gears for mechanical devices can be produced with CNC milling.
4. Fittings: Milled fittings are used to join two or more pieces together.
5. Mold Tooling: CNC milling of steel or aluminum tooling allows for quick prototyping of molded items.
6. Forming Punches: CNC mills can create manufacturing equipment such as sheet metal forming punches.
7. Engine Parts: Automotive engineers use CNC milling to produce engine blocks and other parts.
8. Medical Devices: CNC milling is used for manufacturing implants, surgical instruments, and other medical items.
9. Brackets: Milled brackets can have unique threads and holes and are more intricate than sheet metal brackets.
10. Water Pumps: Multi-axis CNC mills can create reliable impellers for hydraulic systems.
Examples of Parts Made with CNC Turning
1. Shafts: CNC turning is ideal for producing shafts with rounded profiles.
2. Turbines: CNC turning is used to manufacture round turbine blades for the energy industry.
3. Flanges: CNC-turned flanges are used to reinforce beams and pipes.
4. Ball Joints: CNC turning is perfect for circular connecting devices such as ball joints.
5. Rollers: CNC lathes can produce rollers with tight tolerances for industrial applications.
6. Nozzles: Nozzles, typically cylindrical or conical, have hollow interiors making them ideal for CNC turning machines.
7. Firearms: CNC lathes can create the tubular shapes required for weapon barrels.
8. Bolts and Nuts: CNC turning is accurate enough for producing tolerance-critical components like bolts and nuts.
CNC Milling vs. CNC Turning: When Should You Use Which?
While CNC machines offer numerous benefits, it's essential for businesses to consider the design requirements before choosing the most suitable CNC machining operation for each project. If you're unsure, a skilled machinist can help guide you in selecting the best process for your needs. Below are some useful guidelines to help you make the right choice:
When to Use CNC Milling?
CNC milling uses rotating cutting tools to remove material from a stationary workpiece, making it ideal for projects that do not require cylindrical components. CNC milling is well-suited for machining flat or uneven surfaces and is commonly used for secondary finishing processes due to its ability to produce precise design features. If your project involves complex shapes or intricate detailing, CNC milling is likely the better option.
When to Choose CNC Turning?
CNC turning involves rotating the workpiece while the cutting tool removes excess material. This process is preferred for manufacturing cylindrical or round shapes. The high-speed rotation of the workpiece, coupled with CNC turning's broad material compatibility, makes it particularly ideal for large-scale production of tubular or symmetrical parts. If your project requires high-volume production of cylindrical components, CNC turning is the most efficient choice.
Is Milling Cheaper Than Turning?
Producers generally fabricate turned items at a substantially cheaper cost than milled components. This is because CNC lathes processes enable the effective manufacture of several pieces in a short period, hence minimizing additional expenses incurred due to manufacturing faults.
