Machined parts are prevalent across industries. They represent a category of precision engineered components, made by subtractive processes to strict tolerances, and delivering complex geometries, repeatable accuracy, and superior surface finishes. This guide covers the basics of machined parts and components: what they are, how they’re produced, their advantages, and key design principles. You’ll also learn about the materials used and their applications.
What Are Machined Parts and Components?
Machined parts and components are precision objects created by removing excess material from a solid block, or “workpiece”. Cutting machines— such as lathes, mills, drills, and routers— shape the workpiece to the desired form and finish. These parts can be made from metals, plastics, or other materials that maintain dimensional stability during cutting.
Machining can be performed in two main ways:
Manual Machining: Operated by a skilled machinist who controls the tool movement directly, often using handwheels or levers.
CNC Machining: Fully automated using pre-programmed digital instructions, allowing for complex geometries, repeatability, and high efficiency—particularly for custom or high-precision parts.
Most complex or custom components are made on CNC machines for maximum precision and scalability. Nonetheless, manual machining still has its place—especially for quick, one off parts where setting up a CNC program would take longer than simply cutting by hand.
In some cases, machining is used as a secondary or finishing process. For example, a part might be initially cast, forged, or injection-molded, and then undergo additional machining to refine its features—such as drilled holes, tapped threads, or milled surfaces. These are often referred to as partially machined or post-machined parts.
Common Machining Techniques and Processes
From simple holes to complex internal geometries, different machining techniques shape the key characteristics of machined parts. Below are some of the most widely used machining methods:
Milling: Uses rotating multi-point cutting tools to remove material from a workpiece along multiple axes. This process is highly versatile for creating complex surfaces, pockets, slots, and contoured shapes with high accuracy. The common types of milling operations include face milling, end milling, and slot milling.
Turning: The workpiece spins against a relatively stationary cutting tool to generate cylindrical features—shafts, rods, and bushings—with tight dimensional control and smooth finishes.
Drilling: A rotating drill bit creates holes of various sizes and depths. It is one of the most fundamental machining processes, widely used for through-holes, blind holes, and threaded holes in mechanical parts.
Broaching: A toothed broach, with progressively larger teeth, cuts material in a single pass. It is particularly useful for cutting internal features like keyways, splines, and non round holes.
Grinding: A rotating abrasive wheel refines surface geometry and finishes to very tight tolerances. This technique is often used as a final finishing step for high-precision parts.
Electrical Discharge Machining (EDM): Electrical sparks in a dielectric fluid erode conductive workpiece material, enabling the creation of intricate shapes, sharp corners, and deep cavities in hard or delicate metals.
Laser Cutting: Uses a focused laser beam to melt, vaporize, or burn material, enabling precise and contact-free cutting. It is suitable for metals, plastics, and other materials, particularly in thin sheet form.
Ultrasonic Machining: Ultrasonic vibrations transmit an abrasive slurry against the workpiece, removing material from brittle or heat sensitive materials (e.g., ceramics, glass) without thermal damage or mechanical stresses.
What Are the Advantages of Machined Parts?
CNC machined parts offer several key advantages over 3D printed and injection molded components. These benefits include:
No Minimum Order Quantity (MOQ)
One of the main advantages of machined parts is that you don’t need a minimum order quantity to purchase them. You can order a single prototype or very small quantities on demand— without the costly, time consuming tooling required for molded parts. This is especially useful for smaller companies, as it reduces inventory and capital tie up and supports customized production.
Good Prototypes
Machined parts are suitable and affordable as prototypes because they avoid expensive tooling and minimum order requirements. Programming and setup typically take only a few days, so teams can rapidly iterate designs and evaluate each version’s fit and function in real world tests. The high precision and superior surface finish of CNC machining ensure prototypes closely resemble final production parts, even for complex geometries or intricate details.
Moreover, machining supports a wide range of materials—from aluminum and steel alloys to engineering plastics— developers can test multiple options under actual operating conditions and identify the optimal substrate before committing to large scale manufacturing.
Design Freedom
Machining offers unmatched design freedom by using multi-axis cutting tools to produce nearly any shape— deep pockets, undercuts, sharp corners, and intricate contours. You can integrate features such as threads, bosses, and keyways in a single setup, rather than designing separate inserts or adding them later.
Injection molding, by contrast, demands design concessions—uniform wall thicknesses, draft angles, and consistent flow paths—to ensure proper mold filling and part ejection. Once the mold is built, modifying that design usually requires expensive tool changes or even a complete mold rebuild.
Even 3D printing process, generally seen as one of the best manufacturing processes in terms of design freedom, has limitations. Most additive methods (especially FDM and SLA) cannot build steep overhangs without support structures. Those supports add material, increase print time, and must be removed post-print—often leaving marks that need sanding or other finishing. Large or intricate parts may warp as layers cool, and the layer-by-layer build leads to anisotropic strength and visible “stepping” on vertical surfaces.
Strength
Machined parts are cut from solid billets, which retain the full strength and material integrity of the stock. This makes them structurally superior to 3D printed parts, which can suffer from interlayer weaknesses, and to molded parts, which may require thinner walls for flow considerations.
Faster Lead Times
Machined parts are produced much faster because there’s no mold or special tooling to build. Once your CAD model is ready, a CAM program can be generated and sent directly to the machine. Modern CNC centers can operate around the clock with minimal supervision, allowing parts to be fabricated in just a few days. This speed is especially beneficial for rapid prototyping, bridge production, and urgent replacement needs.
Surface Finish
Machined parts can achieve smooth, high-quality surface finishes without the flow lines, flash, or parting lines often seen in molded parts—or the layer lines from 3D printing. By combining high spindle speeds, optimized feed rates, and proper coolant, machining can routinely achieve roughness values (Ra) below 0.8 µm—and with fine finishing passes, even down to 0.2 µm or better.
Quality
CNC machines can hold tight tolerances and deliver consistent results from part to part. If a given feature—such as a precision bore that must seal perfectly—requires special attention, the machinist can spend extra time or make additional finishing passes on that feature without affecting the rest of the part.
By contrast, injection molded parts depend entirely on the mold cavity’s initial accuracy. After thousands of cycles, tool wear and slight process shifts can round off edges or change dimensions, and you can’t tweak individual pieces without costly mold adjustments or secondary operations.
Easy Alterations
Because CNC parts are produced directly from digital CAD files, you can make design changes right up until fabrication starts. This is invaluable during R&D and prototyping: engineers can fine-tune dimensions or test multiple versions without extra cost or wasted material.
How to Design Machined Parts?
When designing machined parts, it is generally advisable to follow design for manufacturing (DFM) principles to ensure functionality, accuracy, and cost-efficiency. Fortunately, machined parts are not particularly difficult to design when you follow key machining design considerations below:
Wall Thickness
Thin walls are prone to deflection and vibration during machining, which can lead to dimensional inaccuracies and poor surface finish. As a general guideline, wall thickness should be no less than 0.8 mm for metal parts and 1.5 mm for plastic parts.
Undercuts
Undercuts are recessed features that cannot be reached with standard cutting tools due to obstructing geometry. They require specialized tools, such as T-slot or L-shaped cutters, as well as additional machine setups and tool changes. For this reason, undercuts should only be used when necessary to the function of the part—for example, when a locking groove, keyway, or assembly feature cannot be achieved by any other means.
When designing undercuts in machining, it's best to make their dimensions in whole millimeters to match standard tool sizes. Undercut widths typically range from 3 to 40 mm, with depths up to twice the width.
Protrusions
Tall, narrow protruding features—such as bosses or posts—are difficult to machine accurately and may cause tool chatter, vibration, or part distortion. To maintain stability and accuracy, the height of a protrusion should not exceed four times its width. Additionally, adding ribs or fillets can effectively reinforce protruding features and reduce stress concentration, making them more stable during the machining process.
Cavities, Holes, and Threads
Cavities and pockets should be no deeper than four times their width to ensure proper chip evacuation and prevent tool deflection. Because end mills have a circular profile, internal corners always have a radius—so avoid specifying perfectly sharp inside edges.
Holes are typically made with drill bits or end mills. Since drill bits come in standard sizes, match hole diameters to standard tooling whenever possible. Also, limit hole depth to four times the diameter to maintain tool stability and drilling accuracy.
Threads can be machined down to small sizes (e.g., M6 and below), but must balance strength and efficiency. As a guideline, use an engagement length of at least 1.5 × nominal diameter (up to a practical maximum of 3 × diameter). Beyond that, extra threads add machining time and tool wear without significant load carrying benefit.
Scale
The size of a part must fit the capabilities of the machining equipment. For most milling operations, typical part dimensions should not exceed 400 × 250 × 150 mm. Larger parts may require advanced vertical or horizontal machining centers. Certain 5-axis milling machines can handle components up to 1000 × 1000 mm or even larger. For standard turning processes, the maximum workable size is about Ø 500 mm × 1000 mm.
Minimum part size is generally limited by tool diameter and machine precision. For instance, if a feature is smaller than the tool itself, it cannot be machined. On standard machines, the minimum feature size typically ranges from 0.5 mm to 1 mm. For extremely small parts, micro-machining equipment or ultra-precision processes may be required to achieve the desired geometry.
Machined Part Materials
Machined parts can be made from a wide variety of materials . The CNC machining material you select influences both mechanical properties—such as strength, weight, and corrosion resistance—and machining characteristics like cutting speed, tool wear, and surface finish. Softer materials are easier to cut but may deform; harder materials demand slower feeds and specialized tooling.
Below are some materials commonly used for machined parts:
A variety of post-processing options can be applied to machined parts to improve surface texture, appearance, and performance. Below are common surface finishes for CNC-machined parts:
As-Machined: No additional surface treatment. It reflects the natural surface condition of the part as it comes directly off the machine. Slight tool marks and surface variations may be visible. It is suitable for internal, non-cosmetic, or purely functional parts.
Bead Blasted: Abrasive media is blasted at the surface to create a uniform, matte texture. It helps remove burrs, sharp edges, and machining marks. However, it’s important to note that the blasting process removes a small amount of material from the part, which may affect tight tolerances and delicate features.
Anodized: An electrochemical process commonly used on aluminum parts to improve corrosion and wear resistance. Type II anodizing creates a decorative and corrosion-resistant coating available in various colors. Type III anodizing (hard anodizing) produces a thicker, denser layer, offering greater abrasion and chemical resistance.
Powder Coated: Dry powder is sprayed onto the surface of the part, which is then heat-cured in an oven to form a hard, colored coating. This finish offers a strong, wear-resistant, and corrosion-resistant layer that is more durable than standard paint coatings.
Polished: A mechanical process that uses fine abrasives or buffing wheels to achieve a smooth, reflective surface. Polishing improves aesthetics and can reduce surface roughness for components requiring low friction or visual appeal.
Machined Part Tolerances
Machining tolerances are the permissible range of dimensional deviation, showing how much a finished part may differ from its nominal design dimensions. The tighter the tolerance, the higher the machining precision—and the greater the manufacturing difficulty and cost. Components requiring precise fits or critical functions demand tight tolerances, while noncritical parts can be made to looser, more cost effective tolerances.
There are several international standards for machining tolerances, with ISO 2768 being one of the most widely adopted. This standard provides general metric tolerances (in millimeters) for linear and angular dimensions without requiring individual tolerance specifications. It classifies tolerances into four grades and helps manufacturers reduce ambiguity, maintain consistency, and optimize production costs. See the tables below:
Basic size range in mm
Permissible deviations in mm
f(fine)
m(medium)
c(coarse)
v(very coarse)
0.5 up to 3
±0.05
±0.1
±0.2
-
over 3 up to 6
±0.05
±0.1
±0.3
±0.5
over 6 up to 30
±0.1
±0.2
±0.5
±1.0
over 30 up to 120
±0.15
±0.3
±0.8
±1.5
over 120 up to 400
±0.2
±0.5
±1.2
±2.5
over 400 up to 1000
±0.3
±0.8
±2.0
±4.0
over 1000 up to 2000
±0.5
±1.2
±3.0
±6.0
over 2000 up to 4000
-
±2.0
±4.0
±8.0
The tolerance class designation for linear dimensions, per the ISO 2768 standard
Basic size range in mm (shorter side of the angle concerned)
Permissible deviations in degrees and minutes
f(fine)
m(medium)
c(coarse)
v(very coarse)
up to 10
±1º
±1º
±1º30
±3º
over 10 up to 50
±0º30
±0º30
±1º
±2º
over 50 up to 120
±0º20′
±0º20′
±0º30′
±1º
over 120 up to 400
±0º10′
±0º10′
±0º15′
±0º30′
over 400
±0º5′
±0º5′
±0º10′
±0º20′
The general tolerances for angles/angular dimensions
What Are the Applications of Machined Parts?
Machining is used across industries to produce precise, durable components—such as valve bodies, gears, housings, fasteners, and brackets—in both prototyping and full scale production. Below are key industries that use machined parts:
Aerospace
The aerospace industry requires machined parts that meet the highest performance and safety standards. These components must withstand extreme pressure, temperature variations, and mechanical loads while maintaining minimal weight. CNC machining supports complex geometries and micron-level tolerances required in this field.
Typical applications:
Turbine blades and housings
Fuel system components and engine mounts
Landing gear shafts and structural supports
Satellite components and communication system housings
Medical
Precision and biocompatibility are paramount in medical device manufacturing. CNC machining enables the production of high-accuracy parts with smooth finishes and tight tolerances, suitable for implants and high-performance surgical instruments. It also supports a wide range of certified medical-grade materials.
Typical applications:
Orthopedic implants (hip/knee replacements, bone screws)
Surgical instruments and tools
Diagnostic equipment housings and mechanical subsystems
Dental implants and intraoral components
Automotive
CNC machining is widely used in automotive engineering to produce reliable, high-strength components for drivetrains, power systems, and chassis assemblies. Machining allows for fast iteration in performance tuning and prototyping, while supporting large-scale production of precision mechanical parts.
Typical applications:
Engine blocks, pistons, cylinder heads
Transmission components: shafts, gears, housings
Brake system parts and structural fasteners
Custom performance or restoration parts
Consumer Electronics
In the electronics industry, components must be both compact and thermally reliable. CNC machining is used to produce enclosures, cooling structures, and connector housings with high dimensional accuracy and excellent surface finish, often for low-volume production.
Typical applications:
Heat sinks and EMI shielding components
Precision-machined aluminum or plastic enclosures
Connectors, spacers, and mounting hardware
Custom device prototypes
Machined components are also widely used in defense, robotics, renewable energy, and industrial equipment. Their strength, precision, and reliability make them well-suited for high-performance parts operating under mechanical stress, thermal variation, and harsh conditions.
How to Select Machining Parts Suppliers?
From overall product quality and design accuracy to the finer details of tight tolerances and specialized materials, selecting the right machining parts supplier is critical to project success. In this section, we outline some key factors to consider when evaluating CNC machining suppliers :
Certifications: Look for suppliers with ISO9001 or industry-specific certifications that demonstrate quality management and process control.
Engineering Communication: Evaluate how well the supplier understands your design requirements. Clear responses and insightful questions usually reflect deep machining know how.
Reputation & References: Ask other product teams about their supplier experiences. First-hand feedback is often the most reliable filter.
Facility Transparency: If possible, visit the supplier or arrange a virtual audit to assess equipment, process flow, capacity, and quality control measures.
Quoting & Lead Times: Request quotes (RFQs) from multiple suppliers to compare pricing, responsiveness, flexibility, and lead times—especially for international shipments.
To ensure smoother collaboration:
Follow DFM (Design for Machining) principles in your CAD models
Include detailed 2D drawings with standard tolerances and notation
Use NDAs to protect proprietary designs
Clarify payment terms—prepayment is often required for first orders
Work with Chiggo for Custom Machined Parts
Chiggo is a reliable partner offering CNC machining services for your rapid prototyping and on-demand machined parts needs. With extensive experience across diverse industries, we understand the importance of both speed and precision.
Our machine shop is equipped with advanced machining centers and supported by a robust quality management system, enabling us to deliver high-quality components at competitive prices and with shorter lead times. Contact us today to order your machined parts!
