CNC Milling Process Explained: How to Make Precision Parts

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CNC (Computer Numerical Control) machines use computer-controlled systems to automate and streamline manufacturing processes. Back in the good ole days you needed to slowly turn a hand crank and hope that you didn’t miscount how many revolutions you’d already made. The automation of CNC milling has resulted in higher precision, accuracy, and production rates of manufactured parts. 

In this article we provide a comprehensive understanding of the different types of CNC milling and machining and the types of materials, uses, and advantages in modern manufacturing.

What is Milling? 

CNC milling is a manufacturing process that uses computer-controlled toolpaths to machine metal, plastic and other materials in different shapes and parts. The milling machine is controlled by a computer program that translates digital design files into commands for the machine to follow.

CNC milling started gaining popularity in the manufacturing industry in the 1960s. Today, CNC machining; including milling, laser cutting, and waterjet cutting are widely used manufacturing processes across various industries, including automotive, aerospace, electronics, and medical. These machines are able to cut at extremely high levels of precision and accuracy and offer higher production rates versus manual milling.

What is the Difference Between CNC Milling vs. Lathing vs. Turning? 

CNC milling, lathing and turning are all processes that use a machine to remove material from a solid block of metal. These three types of CNC machining offer incredibly high accuracy due to the use of CNC software to programmatically control every aspect of the machining process from start to finish. Lathe and turning tools are held in a rotating fixture in order to make cuts; whereas CNC mills hold the workpiece on a (typically) stationary bed.

CNC Milling vs Laser Cutting vs Waterjet Cutting

At SendCutSend our CNC machining equipment includes laser cutting and waterjet cutting machines. Laser cutting is a thermal process that uses a high-powered laser beam to cut through materials. It is typically used for cutting flat 2D shapes out of sheet materials, such as metals, plastics, and wood

Waterjet cutting is a similar process to laser cutting, but instead of using a laser, it uses a high-pressure jet of water mixed with abrasive particles to cut through materials. Waterjet cutting is versatile and can be used with a wide range of materials, including metals, plastics, and composites. Both laser and waterjets produce high-quality cuts with clean edges and minimal burrs.

CNC Milling Process: How Does It Work? 

CNC milling uses a variety of cutters to remove material from a piece of material to create a three-dimensional object. Milling machines are generally classified as horizontal or vertical depending on the direction in which they move (horizontal machines move back and forth along their X axis; vertical machines move up and down along their Z axis).

If you’ve ever seen someone using an electric drill to make holes in wood, then you’ve seen how milling works at its most basic level: A rotating bit spins rapidly while being pushed into whatever material you’re working with, removing small chips of that material as it goes along until there’s nothing left but an empty hole where once stood the material.

These are the main steps involved in the CNC milling process:

Creating your CAD model 

The process begins with the creation of a Computer-Aided Design (CAD) model of the part that needs to be machined. Using specialized CAD software you can define the part’s dimensions, geometry, and features.

Converting the CAD model into a CNC program 

Once the CAD model is created, it needs to be converted into a CNC program that the milling machine can understand. This is typically done using Computer-Aided Manufacturing (CAM) software, which generates the tool paths, cutting parameters, and other instructions necessary for the milling machine to produce the part. If SendCutSend is manufacturing the parts, we do the CAM for you.

Setting up the milling machine 

The milling machine needs to be set up for the specific job. This involves attaching the appropriate cutting tools, securing the workpiece on the milling table, and aligning it accurately according to the CAD model’s specifications. Additionally, the CNC program is input into the machine’s control system. 

Carrying out the milling operations 

With the milling machine properly set up, the CNC program controls the movement of the cutting tools in multiple axes, precisely removing material from the workpiece according to the defined tool paths. 

Finishing operations

Depending on the requirements of the part, additional finishing operations may be needed, such as deburring, polishing, or surface treatments. These operations are done manually or using secondary CNC machining processes to achieve the desired final appearance and functional properties of the part.

Advantages and Disadvantages of CNC Milling Machines

The advantages and disadvantages of CNC milling can vary depending on the specific application, industry, and production requirements.

Advantages 

High Precision

CNC milling machines offer unparalleled precision, allowing for the production of complex parts with tight tolerances and fine details.

Increased Productivity

CNC machines are highly automated, reducing the need for manual labor and increasing production rates, resulting in higher productivity.

Improved Accuracy

These machines follow programmed instructions precisely, eliminating human error and ensuring consistent and accurate results.

Flexibility and Versatility

CNC machines are capable of machining a wide range of materials, including metals, plastics, composites, and more. They can also produce parts with complex shapes, contours, and features, making them highly versatile for various applications and industries.

Customization and Repeatable Results

CNC milling allows for easy customization and quick changes to the design or specifications of the part, making it ideal for prototyping and iterative design processes. It also ensures consistent and repeatable results, reducing variability and improving quality control.

Disadvantages 

Not Ideal for All Projects

Depending on the type of project you’re looking to have cut, CNC milling may not be the best piece of manufacturing equipment for the job. Seeking a manufacturer that offers additional CNC machining, such as laser cutting and waterjet cutting can assure your parts can get produced.

Higher Costs for Initial Investment

CNC milling machines can be expensive to purchase and set up, requiring a substantial initial investment. Small-scale manufacturers or businesses with limited budgets may find it challenging to afford CNC milling equipment.

Operator Skill and Training

While CNC milling machines are highly automated, they still require skilled operators who are proficient in CAD/CAM programming, machine setup, and operation. The training and expertise needed to operate CNC milling machines may be a barrier for some businesses.

Maintenance and Repair

CNC machinery requires regular maintenance, such as tool changes, spindle lubrication, and machine calibration, to ensure optimal performance. Additionally, if a machine breaks down, it may require specialized repairs that can be time-consuming and costly.

Material Limitations

CNC milling may have limitations in machining certain materials, such as extremely hard or brittle materials, or materials that produce toxic fumes or dust during machining. Special considerations and additional safety measures may be required for machining such materials.

Alternatives to CNC Milling: Laser and Waterjet Cutting

Laser cutting and waterjet cutting are both excellent alternatives to CNC milling in certain applications. In many ways they can make up for the shortcomings of CNC milling and the applications where they work better:

  1. Precision and accuracy: Laser cutting and waterjet cutting can cut intricate shapes and designs with a high degree of accuracy and consistency. This makes them ideal for applications where precision is critical, such as in the aerospace and medical industries.
  2. Material flexibility: CNC milling is limited to certain materials, such as metals and plastics. Laser cutting and waterjet cutting, on the other hand, can cut through a wide range of materials, including metals, plastics, wood, ceramics, and even glass. This makes them more versatile and useful in a wider range of applications.
  3. Cost-effectiveness: Laser cutting and waterjet cutting can be more cost-effective than CNC milling, especially when it comes to cutting thicker materials. CNC milling can be slow and expensive when cutting through thick materials.
  4. Non-contact cutting: Laser cutting and waterjet cutting are both non-contact cutting methods, which means that there is no physical contact between the cutting tool and the material being cut. This eliminates the risk of damage to the material, which can be a concern with CNC milling.
  5. Complex shapes: Laser cutting and waterjet cutting can cut in any direction and at any angle, making it possible to create intricate designs and shapes that would be difficult or impossible to achieve with CNC milling.

Types of Milling Machine Operations 

From aerospace and automotive to electronics and medical devices, CNC milling is utilized in diverse manufacturing sectors to create precision components for various applications. Whether it’s producing intricate shapes, tight tolerances, or fine details, CNC milling and machining offers the capability to manufacture parts with high precision and accuracy. In this section, we will delve into the main steps involved in the CNC milling process, highlighting its versatility and applicability in different industries.

Types of Milling Machines 

Milling machine classification can be based on machine configuration, the number of axis in motion or a combination of their specific characteristics. 

Horizontal and vertical milling machine configurations are based on the spindle axis relative to the worktable. This difference in orientation affects the types of milling operations that can be performed and the overall versatility of the machine.

Milling machines can also be categorized based on the number of axes they incorporate. The number of axes refers to the number of directions in which the cutting tool can move relative to the workpiece. For example, a 2 axis CNC milling machine only has x-axis and y-axis movement and is restricted to left to right and front to back. A 3 axis CNC milling machine has three axes of movement, and so on up to 5-axis. At 4 and 5 axis an additional rotary axis is added providing even more flexibility and rotation for complex cutting.

The most common milling machine types include:

Knee-type milling machine: 

Knee-type milling machines have a vertically adjustable worktable resting on a saddle that is supported by a knee. The knee can move vertically along the column, allowing the worktable to be positioned at different heights. 

Bed-type milling machine

Bed-type milling machines have a stationary worktable resting on a bed that can be adjusted in height. The spindle moves horizontally along the bed and can also move vertically up and down. 

Ram-type milling machine

Ram-type milling machines have a spindle mounted on a movable housing, called a ram, that can move along the column. This type of machine allows for more versatile milling operations since the spindle can move both horizontally and vertically, and the ram can swivel to perform angled cuts.

Planer-type milling machine

Planer-type milling machines are similar to bed-type milling machines, but the worktable moves along the bed instead of the spindle. The spindle can move vertically and horizontally, allowing for more complex milling operations. 

CNC Milling Materials 

CNC milling can be used to machine a wide range of materials, from metals and alloys to plastics, composites and wood. However, the suitability of a particular material for CNC milling depends on a variety of factors, including the part’s design, required tolerances, and production volume.

When selecting a material for CNC machining, some key factors to consider include:

  1. Hardness: The hardness of the material affects the cutting tool’s ability to penetrate and remove material. Harder materials require stronger cutting tools and slower cutting speeds to prevent tool wear and breakage.
  2. Strength: The strength of the material affects the force required to remove material and the overall durability of the finished part.
  3. Thermal resistance: The ability of the material to withstand heat generated during the cutting process is important to prevent thermal damage to the part or tool.
  4. Cost-effectiveness: The cost of the material can be a significant factor, especially for high-volume production runs.

Different Uses and Applications of CNC Milling 

CNC milling is used in various industries for a wide range of applications due to its high precision, accuracy, and repeatability. Some of the main industrial applications of CNC milling and machining include aerospace, automotive, agriculture and medical. 

  • Aerospace: CNC milling is used to produce critical components for aircraft, such as engine parts, landing gear, and structural components.
  • Automotive: CNC milling is used to produce high-precision parts for engines, transmissions, and other automotive components.
  • Agriculture: CNC milling is used to produce farm machinery parts and equipment, such as seed drills, harvesters, and plows.
  • Medical: CNC milling is used to produce medical implants, prosthetics, and surgical instruments with high precision and accuracy.

Whether you’re a hobbyist or professional CNC machining can be used to make everything from the above listed parts to furniture and home decor. It’s also a beneficial tool for prototyping. For further inspiration on how you can leverage CNC machining check out our customer showcase.

Creating Your Very Own CNC Laser Cut Metal Parts  

CNC milling is just one way to get custom laser cut metal parts. Other manufacturing processes including CNC laser cutting and CNC waterjet cutting can provide additional opportunities for machining custom parts. At SendCutSend we pick the best cutting process based on your design, material type, thickness, and desired add on services. Just upload your CAD file to our app for instant pricing.

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We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Zinc plus Clear Chromate

Aluminum: 5052, 6061, 7075 Steel: Mild, G30

SKUSO-440-8
Thread Size4-40 x .250″
Hole size in sheet (+0.003/-.0.000).168″
Minimum sheet thickness0.040″
Maximum sheet thickness.125″
Fastener materialSteel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole..345″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Length.250″
Aluminum material ranges (5052, 6061, 7075)0.040″-0.125″
Steel material ranges (CRS, HRPO, HR)0.048″-0.119″

We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Passivated

Stainless Steel: 304, 316

SKUSO4-440-8
Thread Size440
Hole size in sheet (+0.003/-.0.000).166″
Minimum sheet thickness0.04″
Maximum sheet thickness.125″
Fastener material400 Stainless Steel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole. Example shown with x2 of the same hardware..313″
Recommended panel materialStainless Steel
Coating typePassivated
Length.250″
304 Stainless Steel material ranges0.048″-0.125″
316 Stainless Steel material ranges0.060″-0.125″