Introduction — What is CNC Machining?

There’s no simple way to describe the benefits of high-quality precision machining and its importance in today’s economy.

Just about any industry that relies on precision machined parts uses CNC machining services to create custom machined parts from raw materials, fabrications, or castings into individual components.

CNC machining, or computer numerical control machining, is a type of precision machining that’s automated, enabling high accuracy and extreme precision. Not only can CNC machining attain a degree of complexity and intricacy that traditional precision machining technology can’t, it’s also cost-effective, especially when producing complex parts.

Getting the Most from CNC Machining

Long gone are the days of people working levers, handling products excessively, and pushing buttons. The computer components of CNC machines manipulate the cutting tools and shape the material.

Extreme precision demands CNC machining. While conventional machining is acceptable for some industries, others require position tolerances of +/- .001” or tighter. And often, tens of thousands of identical parts are needed, which is impossible without CNC’s repeatability.

Nearly every industry benefits from CNC machining, and the types of CNC machines vary as much as the industries they benefit. Before we explore those, let’s cover what CNC machines actually do.

CNC Machined Parts

Reading about high-quality CNC machined parts and projects is fine, but there’s nothing like seeing them! Check out our CNC parts photo gallery Here.

What Does a CNC Machine Do?

Standard CNC machining processes may include the following machining techniques:

  • Milling — bringing a rotating cutting tool into contact with a stationary workpiece
  • Turning — rotating a workpiece to contact a cutting tool; lathes are common
  • Drilling — bringing a rotating cutting tool into contact with a workpiece to create a hole
  • Boring — removing material to form a precise inner cavity within a workpiece
  • Broaching — removing material with a series of shallow cuts
  • Sawing — cutting a narrow slit in a workpiece using a saw blade

What is a CNC Machine?

Additional CNC Machine Shop Services

Beyond advanced machining, a CNC machine shop may provide additional services that elevate a project:

  • Project Management — start-to-finish expertise (design to production) to ensure project scope, cost, quality, and schedule best meet customer needs
  • Procurement — source material and provide experienced advice for the best possible solution
  • Quality Control — control plans, failure modes effects analysis (FMEA), production part approval process (PPAP), supplier quality engineering, and production audits ensure parts meet customer requirements
  • Engineering — a capable engineering team that leads production process design, tool selection and custom design, CNC programming, and fixture design/build provides flexibility, shortens lead times, and enhances quality

Machine Shop Comparison: Precision vs. CNC

Precision machining involves removing material from a workpiece, or blank, to produce a part while maintaining tight tolerances. This is typically done by removing layers of material using milling machines, by turning, or using electrical discharge machining.

Custom CNC machine work, a type of precision machining, is automated, enabling high accuracy and extreme precision (tolerances can be in the single-digit micron range). Not only can CNC machining attain a degree of complexity and customization that traditional precision machining technology can’t, it’s also efficient and cost-effective.

It’s really no contest. Higher production quality. Reliable consistency. Customization. Superior accuracy. Increased efficiency. Reduced labor costs. It’s no wonder that CNC machine shops boast better part performance and happier workforces.

CNC Machine Shop Floor


The Machines of CNC Machining

CNC machining centers are a significant investment, and machine shops leverage the industry’s best-in-class equipment and technologies to be competitive. As you’ve read, CNC machines are capable of making “precision parts.” However, when a CNC machine shop wants to make highly complex, ultra-high-precision parts, it requires advanced machinery, engineering, and proven processes to do it consistently and efficiently.

Types of CNC machines vary greatly. Most perform one or more of the services mentioned above. Typical range of motion includes 3, 4, 3+2, and full 5 axis.

  • Milling Machine
    • Vertical
    • Horizontal
  • Turning Machine (Lathe)
  • Mill-Turning

Vertical vs. Horizontal CNC Machines

There are two main spindle orientations in CNC machining. In vertical CNC machines, the spindle axis, which is called the z-axis, is oriented vertically. In a C-column configuration, the spindle travels in this direction and the table that holds the workpiece moves in both x and y horizontal directions. Vertical machines are perfect for projects milled from one side, such as covers and brackets.

In horizontal CNC machines, the spindle z-axis is horizontal and typically parallel to the length of the machine. The spindle travels the vertical y-axis and horizontally in the x-axis. The pallet and fixtures hold the workpiece and move in the z-axis, and the B-axis rotates. Horizontal machining has several advantages including accessing machining from four sides and better chip evacuation. Typically, heavy workpieces are a better fit for horizontal machines because the machines are more sturdy, include pallet changers and hold more tools and the spindle can machine all sides of the parts using B-axis rotations. As one pallet remains accessible to the operator for loading/unloading, the other operates within the work area, enabling continuous spindle-driven part cutting.

The Importance of Casting

Casting can simplify the process of forming a metal into a complex shaped product. It eliminates the need for many parts to be put together; instead, molten metal is poured into a mold, and the cast is one solid piece.

In CNC manufacturing, cast metal parts most often require machining to be ready to use; they’re not ready to go straight from the mold. Many mechanical features require machining to add characteristics that casting alone cannot do. CNC machine shops work parts to ensure they meet various specifications (shape, design, accuracy, etc.). 

CNC Machining

There are three methods of casting that are more common and cost-efficient than others:

  1. Sand casting is the most versatile casting method for producing many products. A pressed pattern into fine sand forms the mold into which the metal is poured. Sand casting is a more expensive piece price process than die casting (see below), however it’s more economical for intricate designs, small quantities, and large castings. Because iron can’t be put under high pressure, sand is its only casting option.

  2. Die casting forces molten metal into a steel die/mold, creating precisely formed parts (holding tighter tolerances) that require less machining and finishing. Die casting is often used for high-volume production because it’s faster. Die casting means a significant increase in the cost of steel tooling, however the right investment in tooling upfront results in a lower overall piece price.

  3. Mold casting (permanent or semi-permanent) flows metal into the mold using gravity or low-pressure, as opposed to high-pressure die casting. Compared to other methods, permanent mold castings can often be stronger. Semi-permanent mold casting places sand cores in the mold to create internal passageways that are removed by burn/shake out. Tooling is more expensive than sand but less than die casting tooling.



Aluminum is desired for its lightweight and impressive strength. Not only does aluminum create an affordable piece price, it allows for quick cycle times and high-volume production. Early commercial aluminum castings were cookware or decorative items. Modern applications of die cast aluminum include complex shapes or thin-walled enclosures for products ranging from automobiles to sink faucets to toys. Often, less machining is needed, and the finished surface can be very smooth or textured.

A cast part is considered “complex” if it’s large (and also heavy … over 70 pounds), needs unique fixturing, has a tight tolerance, consists of a challenging material, or is difficult to control for pressure testing.

Close relationships with foundries help CNC machine shops control part costs and quality, reduce timelines, and make changes smoothly, especially prior to production when changes aren’t cost-prohibitive. Often the lowest total cost requires balancing costs of casting and machining. For example, removing cast stock may reduce machining but increase fallout from porosity.

CNC Machining Processes


Design For Manufacturing (DFM)

You may have seen this stat: 80% of the cost to manufacture a product is determined in the design stage. Modern designers use design for manufacturing (DFM) guidelines to reduce costs while simplifying how a product is produced, reducing design rework, and maintaining overall quality. DFM is the merging of product design and its production method and can apply to designing parts or components.

Look for the 5 Areas of Emphasis in DFM:

  1. Process — Implementing DFM early in the process is key because as design progresses, changes become more and more expensive and difficult to implement.
  2. Design — Challenging the design (by all stakeholders) helps ensure it’s optimized and simplified, which reduces the time and inventory required to make the product.
  3. Material — Reviewing a material’s cost, physical properties, and machining properties promotes a wise choice (adequate physical properties but not overkill, for instance).
  4. Process/Environment — Scrutinizing the process and physical environment can help reduce the number of  operations required, so process and setup times drop as workflow improves.
  5. Compliance/Testing — Testing and checking compliance are critical. An alignment error can damage parts and/or equipment, hurt productivity, or shut things down.

CNC Machinist

Demand These DFM Services (and enjoy their benefits):

  • Partnering on the front end allows expertise and manufacturing knowledge to enhance the process while reducing potentially costly engineering design changes
  • A build process efficiency review ensures that product design and its method of production are scrutinized, making the process simpler and more cost-effective
  • In-house design team and fixture building provides the opportunity for expedited designs and tooling with very short lead times
  • Input on casting and machining designs prior to launch, including design review and advanced product quality planning (APQP), saves money and increases agility during development
  • Prototype services allow for timely review of both cast and machine tools, which helps rapid prototype delivery
  • In-house robotics and PLC programming provide confidence that efficiency, repeatability, and flexibility are maximized from start to finish, whether its repetitive tasks or quality control

Key Performance Indicators (KPIs)

As complex as precision CNC machining can be, customers have one simple need: a perfect part (that meets the deadline and includes superior service, of course). That one “simple need,” however, involves meeting many key performance indicators (KPIs) within a CNC machine shop.

Manufacturing KPIs help evaluate performance in order to make smart adjustments, and there could be dozens for one part alone. How do you choose which to implement?

Start by selecting KPIs that are most relevant and most powerful. Start by tracking current performance, taking note of trends. Then, push to make improvements and set goals.

Assign tasks to individuals who can complete them and report back. Goals may change over just a few weeks; so altering KPIs should become a habit. Think of KPIs as ways to make improvements, not as proof of poor performance.


Quality Control (QMS)

Quality is the heart of CNC machining, and controlling quality is critical in identifying and correcting poor parts before they get to customers. So, of course, most CNC machine shops claim that they meet every quality requirement. But, there’s no way to know for sure, right?

Well, a quality control process called a Quality Management System (QMS) helps guarantee that products/services meet regulatory requirements — ISO 9001:2015 and IATF 16949:2016 — AND customers’ requirements.

The right QMS reminds of regular maintenance/calibration of equipment, keeps training procedures and processes on schedule, drives continuous improvement initiatives, helps select an internal audit team, as well as its ultimate goal: ensuring shipped parts are of the highest quality.

Trends in Precision CNC Machining


Computer-Aided Manufacturing (CAM)

Software, such as MasterCam, helps program a part’s manufacturing by inserting a 3D computer-aided design (CAD) model into a virtual setup. Next, tool sets are added and operations are designed and simulated.

CNC CAD at work

Advanced collision detection mitigates this risk as well as improves part machining thanks to the simulation. This is especially beneficial as multi-axis machining becomes more common (see below).

Tribal knowledge can be built into the CAM software, so years of experience is shared and used. Machinists can access instructions that incorporate a CNC machine’s platform, tool specifications, and best pathing, leading to less downtime and increased production.


Increase in Multi-Axis and Multi-Function CNC Machining Centers

5-axis and multi-function CNC machining centers add simultaneous control of a workpiece’s A-axis rotation in addition to its XYZ motion and B rotation. Multi-function machines integrate functions like turning and milling.

Combining operations is one benefit of more axes and multi-function machines, which means the labor cost per part is decreased. The number of operation steps (with potential for operator error) is reduced as is scrap. Eliminating re-fixturing improves accuracy.

Machines can be upgraded with interchangeable rotary tables. A 3-axis machining center converts to a 3+2-axis machine by adding tilt and rotation of the workpiece. Or, a machine can have dedicated, pre-installed rotary axes. Better CAM software inspires 5-axis machining centers by optimizing the use of guiding curves for tool pathing, which improves live-contouring material removal.


Robots and Artificial Intelligence in CNC Machining

Robots work alongside humans and improve operator productivity by taking on repetitive work such as loading and unloading. Reducing human error, which also improves daily production output, complements the improvements in tooling options and fixturing also realized with robots.

CNC Machining Robotic Trends

Programming robots is straightforward, meaning they’re “taught” motions and behavior as a sequence of points and functions. Operations can update robots to adjust to changes and issues without relying on engineering. Collaborative robots, or cobots, assist with simple tasks as well as within a multi-functional manufacturing environment.

CNC Machine AI

Artificial intelligence (AI) in CNC machining meets two goals: increase efficiency and productivity. AI’s strength is in analytics and real-time data, learning as it goes and providing insights. A CNC machine operator can instantly optimize a machine’s performance.


Industrial Internet of Things (IIOT)

A software dashboard gathers and reports on incoming data from any number of operations within the industrial Internet of things (IIOT). Machines output data, which is used for monitoring/scheduling work and other software-augmented suggestions. One example is integrating a CNC machine with Enterprise Resource Planning (ERP) software.

Trends can be identified to help apply resources effectively to improve operations. Also, any action taken can be measured and improved upon. Preventative maintenance improves with IIOT input, too, as predictive models plan for scheduled downtime.

Many industries benefit from CNC machining including industrial equipment, aerospace, agriculture, automotive and on-highway, construction and off-highway, recreation and consumer goods, power generation, marine, and more.

CNC Machine_agriculture

CNC Machine Operators — The Driving Force

Simply put, a CNC machine operator transforms metal castings into working machined parts. Sounds easy, but it requires a unique mix of brains and hands-on attention to shape a metal casting into a part that meets exact specifications.

CNC Machine Operator

Responsibilities of a CNC Machine Operator

Diligence is vital for CNC machine operators because they’re constantly refocusing between different tasks: loading, unloading, deburring and inspecting parts, and changing tools. All tasks need to be completed thoroughly and quickly.

Specific responsibilities include:

  • Gathering supplies for each day’s work
  • Communicating with other operators (usually about a machine or part quality)
  • Checking loading instructions for a part
  • Loading/unloading finished parts
  • Deburring parts
  • Monitoring tooling

Quality control needs a separate mention. An eye for detail is one of the top traits of a high-end CNC machine operator. All parts are deburred — removing sharp edges and any small metal pieces still attached to the part after machining. Parts are sampled for in-process audits.

CNC Operators Quality Control

Part dimensions are checked using different measuring tools: caliper, bore gauge, pin gauge, thread gauge, depth gauge, and both ID and OD micrometers. Parts are inspected by quality assurance on a Coordinate Measuring Machine (CMM) to verify all dimensions and positions are in tolerance. An operator also listens to the machine during use, paying attention to anything that sounds different than normal and hearing the machine’s alarm for tool life being met.


What Training Does a CNC Operator Complete?

Internal training for operators naturally happens within a machine shop as experienced operators pass along real-world knowledge and processes to new employees. Successful training requires a hunger to learn and diligence to properly run machines.

CNC machinists can become operators of any number of machines, from a CNC lathe to a CNC robotic cell to many others (see “Types of CNC machines” mentioned above).

External training can be gained at a local technical school or community college that offers classes in math, 3D design, blueprint reading, and specialized CNC machinist training.

The National Institute for Metalworking Skills (NIMS) offers many machining certifications within three levels, ensuring a machinist’s skills meet national standards. from entry-level programming and operating of CNC equipment to mastery of CNC milling and turning.


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