The CNC Machining Technology Best Practices for Manufacturing Your Precision Parts

From tiny medical implants to enormous turbine blades for power generation, the millions of components required for today’s technology depend on precise manufacturing techniques. To accomplish this, original equipment manufacturers rely on the services of CNC machine shops to fabricate the parts they design. Using a combination of CNC milling machines and lathes, the modern machine shop can create incredibly intricate parts to dimensional tolerances of three-thousandth of an inch or better.

At Plethora, we know that building components precisely requires the best CNC machines, machinists, and manufacturing processes. Therefore, we built our business on the foundation of using the finest tools, personnel, and processes to deliver only the highest quality parts. We understand that fabricated parts may suffer from poor quality or excessive amounts of time and expense in their manufacturing without this level of detail. The following includes some CNC machining best practices we recommend for parts design and that we follow to ensure the highest quality in our parts.

CNC Machining Capabilities

CNC machining relies on two different types of equipment to fabricate parts, the milling machine and the lathe. Both of these machines remove material from the workpiece in a process known as subtractive manufacturing. The CNC milling machine spins a rotating cutting tool to mill material out of a stationary workpiece. A CNC lathe uses a stationary cutting tool to remove material from a spinning workpiece. Some more details about CNC machining equipment and the best practices used to produce precision parts follow:

CNC Milling

A CNC milling machine uses a cutting tool rotating at different speeds to mill material out of a stationary workpiece. The standard mill moves the cutting tool in three axes to cut the paths programmed into it by the CNC G-code. The limitations of their three axes can restrict these highly accurate mills. Machinists can manually reposition the workpiece as required, but this will impact the time needed for manufacturing and possibly the precision of the part.

For more complex parts, we use five axes CNC mills. The Indexed 5-Axis machine will allow both the tool-head and the bed containing the workpiece to rotate between milling operations, while the Continuous 5-Axis machine will move in all five axes during operation. These machines require a higher cost to operate but produce much more complex parts.

CNC mills can fabricate geometrically complex parts by performing different functions, including milling, cutting slots, drilling, routing, and threading holes. They use a variety of cutting tools for each shape to create these different patterns. These tools include reamers, mill ends, hollow mills, thread mills, and regular drill bits.

At Plethora, we support all CNC mills from standard 3-axis machines to indexed and continuous 5-axis mills.

A-mill-shaping-a-part-by-applying-CNC-machining-best-practices

A CNC mill shaping the contours of a part.

A-CNC-lathe-turning-a-cylindrical-part

A CNC lathe turning a part.

CNC Turning

A CNC lathe is the opposite of a mill in that it rotates the workpiece while the cutting tool remains stationary. The workpiece attaches to the lathe’s spindle, which spins it at a high rate of speed, and the cutting tool moves radially and lengthwise to remove the material. Lathes also include a drill positioned at the spindle’s center to bore through the workpieces. Due to the nature of the machine, a lathe primarily fabricates cylindrically shaped parts like tubing, rods, and washers but can do so at a lower cost than using a CNC mill.

For parts that require milling operations in addition to being turned on a lathe, a combination of the two processes is available with live tooling. First, the lathe’s spindle will stop, then the attached milling head will move into position to cut paths or drill holes. This process—also referred to as “mill-turning”—provides a more efficient method of creating complex cylindrical parts.

Shops can configure CNC lathes with different cutting tools for regular turning or live tooling as with a mill. At Plethora, our CNC lathes will support turning both outside and inside features, and we offer live tooling.

Materials

Part of our process of CNC machining best practices involves choosing the right materials for the job. At Plethora, we offer a wide range of standard materials for your project, with the option to order more unique varieties as needed.

Steel and Stainless Steel

Steel is one of the most popular materials used for manufacturing parts. It has high strength and long life, while stainless steel has natural protection from corrosion. Automotive, aerospace, electronic, medical, and food processing industries, among others, use steel materials.

Aluminum

The strength and resistance of aluminum make it an excellent alternative to steel. Medical, automotive, and aerospace industries often opt for aluminum parts.

Copper, Brass, and Bronze

The pliability of these metals makes them easier to work with than steel, lowering both manufacturing times and costs. In addition, these metals offer corrosion resistance and conductivity, making them useful for industries ranging from plumbing to electronics to aerospace.

Plastics

The softness of plastics makes them an ideal choice for evaluation prototypes, while their strength, low weight, and range of colors make them useful in many industries.

How Companies Use CNC Machined Parts

CNC machining suits many different manufacturing purposes and functions:

  • Prototyping: During product development, engineering departments usually need prototype parts built as quickly as possible to avoid design delays. CNC machining can produce quick-turn prototypes effectively. Designers simply upload their data to get an automatic manufacturability analysis and an immediate build quote from the shop. Usually, the parts will be built within three days, keeping the design cycle on schedule.
  • Production: The machine shop can easily scale manufacturing up to full production with the part already uploaded for the prototype build. CNC machining accommodates production changes like this with ease. At Plethora, we regularly support our customers from product development to the end of life of their project.

As we have seen, the versatility of CNC machining seamlessly supports the progression of prototype part development to production build quantities. Simultaneously, it serves a wide range of different industries. At Plethora, we build everything from advanced aerospace components to everyday automotive parts. However, for success, each part must adhere to some basic design guidelines for best practices—covered next.

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Aluminum raw stock ready to be machined into new parts

Design Guidelines for CNC Machining Best Practices

A machined part is only as good as its design. CNC machining equipment has practical limitations, and designers need to understand these or risk designing un-machinable parts. Designers can optimize a design for the most efficient use of CNC equipment and follow specific design rules to ensure the part’s manufacturability. This section will look at all of this to aid in successfully designing a component according to the CNC machining best practices starting with some general limitations of milling and turning parts.

CNC Machining Limitations

Milling machine tools operate and often look like standard drill bits. As such, their shape will produce a limited range of geometries in the workpiece they are milling. For instance, large tools won’t create sharp corners and penetrate to a specific depth prescribed for that tool. Additionally, the milling operation will not cut sharp internal corners in the workpiece.

Lathes also have some limitations, starting with their ability to produce only round or cylindrically shaped parts. In addition, the cutting tools on a lathe will operate within a specific range of motion. Therefore, a machine shop must augment any parts that require more complex work with live tooling or multiple operations on both CNC lathes and mills.

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Simplifying the design will decrease the time and expense of manufacturing.

Design Optimization

An essential part of CNC machining best practices is to optimize the design for the most efficient use of the mills and lathes. Not only will this help make the design more robust, but it will also reduce the amount of time and money spent on manufacturing. Additionally, it will prepare prototype parts for their transition later on into full production quantities.

Simplify the design and consolidate tool usage

Parts that have extraneous features and contours increase fabrication time and expenses. Additionally, each repositioning of the workpiece or tool change will extend the time required for manufacturing. This additional time for part fabrication will quickly balloon when the design moves from prototype to full production. Therefore, the best practice involves simplifying the design as much as possible without sacrificing its intent.

Use standard hole sizes

Although a CNC mill can fabricate almost any hole size, this operation acts more efficiently with a regular drill bit. Therefore, use standard drill sizes for holes as a best practice to decrease manufacturing time and expenses. Designers should also remember that hole depths should equal no more than four times the hole’s diameter, and tapped holes should have a thread length that doesn’t exceed three times the diameter.

Choose materials wisely

Harder materials make the final part stronger but require more time to machine and, therefore, higher manufacturing costs. Choose a softer material as a better practice if a part doesn’t require that much strength. For example, stainless steel takes four times longer to machine than steel, and steel takes four times longer than aluminum.

Design Rules

In addition to optimizing the design for the most efficient CNC machining, follow some basic design rules for the best results. In some cases, machine shops can work around design rule violations, but it usually comes with a higher price tag and longer manufacturing times. Therefore, the CNC machining best practice corrects any of these rule violations before having the part manufactured.

Corners

Avoid sharp internal corners when milling. Due to the cylindrical shape of the cutting tools, each corner should have a radius of at least a third of the cavity depth. This practice speeds up the manufacturing time and produces higher quality internal surface finishes.

Cavity depth

The deeper a part’s cavity, the more time and money it will take to manufacture. Parts that specify depths greater than four times the diameter of the cutting tool may require more expensive processes and specialty tools.

Walls

Avoid tall and thin walls in a design. The material may experience stress during machining resulting in bending due to unexpected vibrations. This bending could create problems maintaining tight tolerances during manufacturing, which will add even more costs and delays.

Text

Text adds both time and expense to the manufacturing of your part—avoid it if possible. However, if including the text is essential, the best practice is to avoid raising or embossing the text. The raised text requires greater material removal compared to engraving.

Avoiding text is another CNC machining best practice to make manufacturing more efficient

Text can slow down manufacturing and add expense. Avoid it if possible.

These best practices will help designers create a more robust part that holds tighter tolerances, reining design costs, and manufacturing schedules. Now we’ll see precisely how to put these best practices into place when submitting a part order to Plethora for CNC machining.

CNC Machining at Plethora

At Plethora, we have the facilities, equipment, staff, and processes standing by and ready to manufacture your precision parts. But before we can get started, we need the complete manufacturing information for a part. Below is the information we need to successfully work on a project and the tools we use to streamline the analysis and ordering process.

Manufacturing Information and Data

Here is the list of manufacturing information and data that we need to build your part:

  • 3D CAD model: We will build parts using the provided data in a 3D CAD model. We can work with data from a variety of CAD tools, including ACIS®, Autodesk Inventor®, CATIA® V5, Creo™ Parametric, IGES, Parasolid®, Pro/ENGINEER®, Siemens PLM Software’s NX™, SolidEdge®, and SolidWorks®.
  • Materials: Let us know which material to use when making the part. We stock many choices, including steel, stainless steel, aluminum, copper, brass, bronze, and various plastics. We can also quickly order material that we don't usually stock.
  • Finishes: Surface finishes provide a better look and protection for visible parts or parts intended for harsh environments and conditions. Finishes can often get overlooked, which could delay manufacturing until we know how to complete the component.
  • 2D drawing: Although the 3D CAD model will contain all of the specific design details, a 2D drawing calls our attention to unique dimensions and tolerances. 2D drawings add value to inspection and serve as a reference for the machinists during manufacturing.
  • ITAR requirements: We need to know upfront if a part falls under the category of items protected by the International Traffic in Arms Regulations (ITAR). This classification changes how we handle all aspects of your part, from data security to material management.

Fortunately, sending us this information is streamlined and contained within the online part ordering system. When placing an order, the online system prompts specific information, like whether or not the part is ITAR controlled.

Online DFM and ordering systems are all part of utilizing CNC machining best practices

After successfully passing the online autoDFM system, this part is ready to be ordered.