Posted February 25, 2021

Exploring Applications of Subtractive Manufacturing

A CNC machine drilling the metal rod with a drill tool

Understanding a manufacturing process’s nuances empowers designers to optimize for that process’s benefits during the early stages of product development. When it comes to precision and quality, design engineers consider subtractive manufacturing the first choice for industries such as automotive, aerospace, defense, and others. Subtractive manufacturing processes include milling and turning for fabricating parts with tight tolerances and complex geometries. Industries leverage their innovations to maintain their product standards and increase productivity. 

What is Subtractive Manufacturing?

The term subtractive manufacturing refers to the process of producing an object by successively removing material from a raw block to achieve the desired shape and dimensions with a CNC computer numerical control (CNC) machine. The process begins when a design engineer submits a CAD model to a machine shop, ideally with an online quoting system. Advanced software analyzes the design and selects tools, toolpaths, and optimal workholdings. CNC machines work with a wide range of materials, including metal, wood, glass, ceramics, plastics, and composites. Subtractive manufacturing offers several key advantages:

  • Smooth surface finishing
  • High precision and geometric accuracy
  • Excellent repeatability
  • High-stress applications
  •  Less costly to machine some parts compared to additive manufacturing
  • Compatibility with a wide range of materials
  • Speed and high productivity

Subtractive manufacturing involves machines with both linear and multi-axis rotational capabilities. Standard 3-axis and 5-axis CNC milling and turning machines fabricate the workpiece from different orientations to achieve complex designs. 

Applications of Subtractive Manufacturing

Many industries that require precision and strength use subtractive manufacturing for producing precision parts. Although the final product may vary, the core application of machining for most industries remains the same. These applications include quick-turn prototyping, fabricating finished parts, and machining for tight tolerances and complex geometries.


Product designers usually need to test a production-ready part for fit, function, and aesthetics during the product design phase. Quick-turn prototyping allows a designer to receive a part that meets design for manufacturing (DfM) within one or two days. The machine shop produces a part with production-quality materials and finishes. Once the prototype is approved for production, programmed code manages all functions of a CNC machine to execute precise tool movements accurately. Additionally, a company can seamlessly scale  production for higher volumes, from a handful of parts to hundreds or thousands of parts. 

Fabricating Finished Parts

Subtractive manufacturing machines metal parts using CNC machining (turning, drilling, boring, milling, reaming), electrical discharge machining (EDM), and water jet cutting to achieve the desired shape. Finishing and post-processing often improve a part’s surface, removing any tool marks or roughness, fulfilling a specific aesthetic, or providing wear resistance. Subtractive manufacturing offers a wide range of surface finishes, including powder coating, bead blasting, anodizing, black oxide, electropolishing, brushing, polishing, smoothing, and many others to finish a part. 

As Machined

Surface roughness for any machined part is measured by average surface roughness (Ra). A standard machined finish will have an Ra of 3.2 μm (125 μin). This finish has the tightest tolerances and no additional cost. Smoothing and polishing can be applied for a minimal extra cost but will affect the tolerances. 

Powder coating

A thin layer of protective polymer is applied to a part, adding higher impact resistance and strong wear against corrosion. This finish can be applied to any metal part but is not suitable for small components and cannot easily be applied to internal cavities. This finish is best for parts that can’t be anodized.

Bead Blasting

Adds a matte or satin finish to a part that removes tool marks. This is a low-cost option for any part, but it can affect dimensions and surface roughness. 

Anodizing Type II (clear of color)

Standard anodizing can add a thin protective layer of ceramic to aluminum and titanium parts. The coating offers good corrosion resistance and minor wear resistance and is aesthetically optimal.

Anodizing Type III (hardcoat)

A thick layer of ceramic coating (typically 50 μm) is applied to a part, providing excellent wear and corrosion durability for aluminum and titanium parts. It offers more dimensional control and can be applied to internal cavities. This finish is the most expensive finishing and can be brittle compared to powder coating.


An electrochemical process polishes, passivates, and deburrs a stainless steel part with a high-quality natural metal finish. Electropolishing improves corrosion resistance and makes a part easier to clean.

Black Oxide

A black conversion coating is applied to improve corrosion resistance and reduce the amount of light reflection on a part. Black oxide coating is highly durable to chipping and corrosion and offers high dimensional stability. 


Brushing is a surface treatment that creates various line patterns on steel or aluminum parts, providing a satin finish. This finish is not advisable for parts that require corrosion resistance.


Machine shops can help determine which coating is best suited for a metal part’s application. Each finish has pros and cons, and sometimes the right finish is a combination of more than one type. 

Tight Tolerances and Geometries

Tolerances determine the room for error in a machined part and are especially critical in high-stress applications such as those in the medical, aerospace, and automotive industries. Subtractive manufacturing makes use of multiple axes milling and turning machines to achieve complex geometries and tighter tolerances.

The conventional 3-axis machine works in a three-dimensional plane (X-, Y- and Z-axis). The advanced 5-axis machines have added rotary motion in two of these 3-axes. These multiple axes allow the machine to create complex geometrical parts from any angle with excellent accuracy and tight tolerances. 

The continuous 5-axis, 5-axis-indexed, and 3-axis CNC milling and turning machines can provide standard tolerance of +/- 0.005 inches for metals and +/- 0.008 inches for plastics. CNC machines can produce holes with a diameter as small as .020 inches. Tight tolerances require smaller tools, and smaller tools remove less material with each pass. These steps involve more production time and expense, so it’s best to work with an experienced machine shop to ensure a part is manufactured as efficiently as possible.

Selecting Subtractive Manufacturing for Your Application

Subtractive manufacturing offers compatibility with a wide range of high-performance metals and plastics, among other materials. No matter the size of your production run, subtractive manufacturing can provide high-quality and precision. Multi-axis milling and turning, such as Plethora’s  3-axis and 5-axis milling and turning provide controlled and complex prototyping services to produce tight tolerances, complex geometry, and excellent surface finishes. Industries use this manufacturing method for its innovative design possibilities, productivity, and cost-efficiency.

Plethora is an ISO 9001-certified machine shop specializing in precision parts using advanced subtractive manufacturing technologies and CNC machining methods. To learn more about our CNC machining solutions, give us a call at 415-726-2256, or you can upload your design files to Quote My Part and get your project started today.

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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, Design, Manufacturing, finishing, CNC machining, Quality, Prototyping