What is Machining Parts: Types, Benefit and Design Guide

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What is Machining Parts: Types, Benefit and Design Guide

If you were to look around you right now, chances are you’ll find machined parts in your surroundings.

Machined parts are virtually everywhere – from electronic devices and furniture to machinery and vehicles – and it’s not hard to see why. These parts offer the reliability and efficiency required for the proper function of machinery.

But what exactly are machined parts? And why are they so significant in the manufacturing industry?

In this comprehensive article, I’ll guide you through everything you need to know about machined components. We’ll explore their definition, types, benefits, and applications. I’ll also share practical design tips that can help you save time and reduce your CNC machining cost.

What Are Machining Parts?

CNC Machining Parts

Machining parts are components that are built using subtractive manufacturing processes such as milling, lathe-turning, drilling, or grinding.

While these machining processes are all different, they have a common fundamental principle. Subtractive manufacturing involves the removal of material from a solid block to produce the desired part.

Further, machining processes can be grouped into two categories:

  • Manual – As the name suggests, manual machining heavily relies on the skills of a machinist. This operator will use machining equipment such as a mill or a lathe to manually cut the workpiece into the desired form.

  • Digital – Digital machining is the go-to manufacturing process. It involves using a computer numerical control (CNC) machine to automatically cut away excess material. The cutting tool follows the computer aided design to generate the required parts.

CNC machining has been a game-changer in the manufacturing industry. It is a cost-effective method of producing metal and plastic parts, and it accommodates even the most complex designs. That being said, some operations call for manual machining.

Benefits of Machined Parts

Machining Parts

Machining parts offer many advantages, hence their widespread use across industries. I have listed some of the benefits that make them desirable below.


A unique aspect of machined parts is that your purchase is not limited by a minimum order quantity. Since this process has a low initial investment, it is cost-efficient for low quantities and even one-off parts.

With molded parts, production can only start after the manufacture of molding tools. This is a time-intensive process that will easily cost thousands of dollars. Therefore, it doesn’t make sense to use this technique for low-volume production.

Machining is an effective way to produce high-quality parts with no MOQ. This makes it a viable solution for small businesses, prototyping, and low-volume production runs.

High Precision:

Have you ever thought about how manufacturers produce high precision parts for aerospace, medical equipment, and automobiles? CNC machining, of course!

CNC machining is recognized for its ability to achieve extremely tight tolerances. This creates accurate parts that you can rely on when precision is critical.

Design Freedom:

CNC machined parts come in all conceivable shapes and sizes. If you’re asking how this is possible, the answer lies in the impressive machining design flexibility.

Machine parts can feature complex geometries, fine details, and elaborate features. This level of design freedom allows for the realization of imaginative concepts. Thanks to its geometric flexibility, CNC machining is often used to produce custom-machined parts.

Quick Production and Prototyping:

As I have previously discussed, the initial tooling costs mean that only large companies can afford to use injection molding in prototyping.

On the other hand, machined parts allow for affordable and rapid prototyping. Machinists can quickly fabricate different versions of a part which facilitates quicker assessment. Fast prototyping means that the production process can begin sooner.

CNC machines have dramatically improved production speeds leading to a shorter time-to-market.

Surface Finish:

Another perk of machined parts is that they eliminate the surface quality concerns associated with other manufacturing processes.

For example, unlike 3D printing, machining processes do not leave a layer of lines on the part surface. Similarly, injection molded parts have surface defects such as flow lines, sink marks, and vacuum voids.

Machining services produce parts with a high-quality surface finish. Moderate finishing and post-processing operations are enough to enhance the surface characteristics of the machined part.


While purchasing a CNC machine is a significant investment, this equipment comes with numerous cost-saving benefits.

For starters, CNC machining allows the machine shop to save on labor costs. And since the machined parts are highly precise, you can avoid expensive rework costs and reduce the amount of scrap.

CNC machining processes do not require elaborate tooling and this reduces the initial capital investment.

Further, changes are simply made to the CAD file in case of design alterations reducing the cost implications. With a process like injection molding, a design shift requires retooling which is done at a significant cost.

Fast Delivery:

Compared to other manufacturing methods, CNC machining offers some of the fastest delivery times. This fabrication technique allows the machine shop to complete prototyping and production relatively fast. This shorter lead time can be a game changer for any business.

Design Guide Of Machined Parts

CNC Machining Design Guide

By this point, we are familiar with the basic principles of machining technology. In this section, I’ll cover the recommended design principles for the most common CNC machined parts.

Internal edges

The industry-recommended minimum vertical corner radius for any inner edges is a third of the cavity depth.

If you employ corner radii that is just over the advised value, you can cut along a circular path rather than a right angle. This creates a part with a better surface finish.

If the part requires a right angle, you can incorporate a T-bone undercut instead of decreasing the corner radius.

Cavities and pockets

When machining cavities and pockets, it’s important to remember that these features depend on end mill tools which have a limitation on their cutting length.

It is advised to stick to a cavity depth of four times the cavity width. Machining deeper cavities would create fillets with rounded edges as opposed to sharp edges.

Thin walls

Wall thickness will affect the quality of the machined part. Thin walls are less stiff and, therefore, they experience more vibrations during machining operations. This may result in reduced accuracy.

To ensure high-quality parts, it is recommended that you use a wall thickness of at least 0.8 mm for metals or 1.5 mm for plastics.

Plastic materials usually have a larger minimum wall thickness requirement to counter warping and softening during machining.

Threads and Holes

Holes are machined using drill bits or end mill tools. If possible, product designers should choose hole diameters that match standard drill bit sizes. This helps avoid extra costs associated with special tooling. The recommended hole depth is four times the nominal diameter.

Threads are a common machining feature used in the application of fasteners. The recommended thread length is three times the nominal diameter.

Small features

Machining small features can be a tough feat. It is generally recommended to avoid such features whenever possible.

Micro-machining entails creating cavities and holes whose diameter is less than 2.5 mm (0.1″). This operation calls for special skills and tools such as a micro-drill.


Undercuts are features that cannot be machined with a standard end mill. These sections are obstructed by the part making them hard to reach using standard cutting tools. Undercuts will generally make production more difficult and expensive.

When designing undercuts, consider using standard dimensions. Standard sizes can be machined with standard tooling rather than the more expensive custom tools.

Text and lettering

Sometimes, machinists need to add lettering to a part. This can be done through embossing or engraving. While embossed text may be easier to read, engraved lettering is the more common choice. The latter requires minimal material removal making it cost-effective and time-saving.

It is recommended that your chosen font be Sans-Serif (without embellished strokes that are challenging to machine.) The minimum recommended font size is 20 points.

Machining Parts Materials

Machining parts can be manufactured using a range of materials including metals, plastics, and composites. The choice of material is based on factors such as cost-efficiency, electrical conductivity, and mechanical characteristics.

CNC machining accommodates different material types. However, some materials are more challenging to work with than others. For example, it is difficult to machine extremely hard materials using cutting tools. The cutting operation will typically cause vibrations resulting in an inferior cut. Also, very soft materials may deform upon contact with the cutting tool.

Let’s explore the most common machined part materials


Metal and metal alloys are widely used in machined parts and assemblies. They are favored for their durability, versatility, and mechanical properties.

Common machined part metal materials include;

  • Stainless steel

  • Aluminum

  • Steel

  • Titanium

  • Copper

  • Bronze


Plastics offer desirable characteristics such as electrical insulation, corrosion resistance, and low weight. Thanks to these properties, plastic parts have found applications in electronics, medical, and automotive industries.

Commonly used plastic materials include;

  • Nylon

  • ABS

  • PVC

  • Polycarbonate

  • PEEK


In addition to metal and plastic materials, machining processes may use composite materials such as carbon-fiber-reinforced polymers (CFRP) and fiberglass composites.

These materials are characterized by an impressive strength-to-weight ratio, corrosion resistance, and exceptional stiffness. These properties have made composites desirable in the aerospace and sports equipment industries.

Machining Parts Tolerances


A CNC machine can make parts with very tight tolerances. This is especially useful for critical parts that mate with other components. Machinists can also employ looser tolerances during prototyping or for parts with no mating prerequisites.

Machining parts tolerances are typically dictated by international tolerance standards. The table below sums up the tolerance standards for linear dimensions.

Machining Parts Surface Finishes

After the production process, machined parts are typically treated to improve their surface finish. Finishes can enhance the look and performance of the CNC parts. I’ll overview the common machining surface finishes.



There is no surface finish process applied to as-machined parts. These parts are used directly from the CNC machines and, therefore, they may have slight imperfections and tool marks. As-machined or as-milled parts are ideal for internal components that do not serve an aesthetic purpose.

Bead blasted:

Bead Blasting

The bead blasting surface finish utilizes ceramic, steel, or glass beads. A blast gun fires the abrasive beads at the machined part at high pressure to create a matte finish. The final look of the surface will depend on the coarseness of the abrasive media. Bead blasting is typically used with plastic, glass, or metal materials.



This chemical finishing technique involves immersing the machined part into an electrolyte solution. This creates an oxide layer that serves both a functional and cosmetic role. There are two types of anodization: Type II and Type III anodization. Type II anodization offers corrosion resistance while Type III provides both wear and corrosion resistance.

Powder coated:

Powder coating is one of the most common finishing processes applied to CNC machined parts. It involves applying a powder coat to the fabricated parts before baking them in an oven. Powder coating offers a diverse range of color options while also forming a high-strength, wear and corrosion-resistant finish.

Applications Of Machined Parts

Machined parts have found extensive applications in virtually all industries. Let’s explore the different fields that have come to rely on this production process.


Precision is crucial in the aerospace industry. Since CNC machining is capable of achieving very tight tolerances, it is an obvious choice in this field. Machinable airplane and spacecraft parts include engine components, control systems, fuel panels, and landing gear parts.


In the medical industry, you’re bound to come across machined titanium and stainless steel parts. They are typically used for surgical tools, medical devices, orthopedic implants, and dental equipment. Precision machining ensures that medical equipment is reliable and safe to use.



Machined parts play an important role in the automotive domain. They are used for engine components, transmission parts, steering systems as well as one-off custom parts. The precision of machined parts ensures optimal function and safety of vehicles.

Consumer Products

A common application of machining is in the production of household goods such as consumer electronics, appliances, and furniture. In this space, parts are machined to provide both function and aesthetics.


Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.