Everything You Need To Know To Find The Best Custom Machined Parts

If you’re in the manufacturing world, you may find yourself in the middle of a common dilemma: choosing between a custom-made solution or an off-the-shelf product. Selecting between custom machined parts and pre-made components can impact the outcome of your project in terms of functionality, aesthetics, and cost-effectiveness. Recent research suggests that 1 in 5 consumers are willing to pay a 20% premium in personalized goods or services. Here, we’ll investigate the advantages and disadvantages of both custom machined parts and off-the-shelf components so you can find the solution that best suits your needs. 

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Quality Fit

Let’s start with an essential consideration for any product: how well does it fit your precise requirements? It’s important to note that custom machined parts are made to fit your exact specifications. The fit is exact and true to your vision. Off-the-shelf products, on the other hand, are mass-produced with standardized dimensions and features. You might experience convenience and cost savings, but they lack the functionality necessary for many applications. Custom-made parts have an overall better quality fit, so that may make it a more enticing option. 

Cost Considerations

Cost is another key consideration, one that will influence many decisions. Off-the-shelf products will usually be more cost-effective upfront because they benefit from mass production cost savings. High-volume production runs with off-the-shelf parts often eliminate costly delays. In contrast, custom fabrication typically involves a higher initial investment, but results in components that meet your exact needs. This can help you avoid costly replacements down the line. Custom machined parts result in greater accuracy and precision, ensuring your products match your specific vision. 

Material Choice

Materials also play an important role in determining which option is the best fit for you. Custom machining allows you to select specific materials that might not be available in pre-made parts. This can be important for durability, weight, or compatibility with other materials. Off-the-shelf products have more limited options, while custom machined parts can be customized to suit your needs. 

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Machined parts play a crucial role in modern manufacturing, offering high precision, durability, and flexibility for various industries. Whether used in aerospace, medical, automotive, or consumer electronics, machined parts provide unmatched accuracy and quality. CNC (Computer Numerical Control) machining, in particular, has revolutionized the way components are manufactured, allowing for automation, repeatability, and efficient production.

This guide provides an in-depth look at machined parts and components, their manufacturing techniques, material selection, applications, and essential factors to consider when choosing a machining partner.

Introduction

Machined parts are everywhere—from aircraft engines to medical implants and even the smartphone in your hand. These components are created by removing excess material from a solid block (bar stock) using various machining techniques. Whether manually or through CNC automation, machining ensures high precision, repeatability, and cost-effectiveness, making it an essential process in modern manufacturing.

In this article, we’ll discuss:

• What machined parts are and how they are produced.
• Different machining techniques are used in the industry.
• Advantages of machined parts over other manufacturing methods.
• Design principles to consider for efficient machining.
• Common materials and surface finishing options.
• Industries that rely on CNC machined components.
• How to choose the right machining partner for your needs.

What Are Machined Parts and Components?

Machined parts are components shaped by cutting tools that remove material from a workpiece. This process, known as subtractive manufacturing, contrasts with additive methods like 3D printing.

Machining techniques include milling, turning, drilling, grinding, and broaching, which transform raw materials into precise components. These parts can be made from metal alloys, plastics, and composite materials and are widely used across different industries due to their high strength, durability, and precision.

Manual vs. CNC Machining

• Manual machining requires human operators to control machines such as lathes, mills, and grinders.
• CNC machining automates the process using computer programming, allowing for faster and more consistent production with minimal human error.

Common Machining Techniques and Processes

Machining processes vary depending on the part design, material and required precision. Below are the most commonly used techniques:

Milling

• A rotating cutting tool removes material from a stationary workpiece.
• Creates contoured surfaces, slots, and drilled holes.
• Used for parts that require complex geometries and precision.

Turning

• The workpiece rotates while a stationary cutting tool removes material.
• Ideal for machining cylindrical components such as shafts, bushings, and threads.

Drilling

• Uses a rotating drill bit to create precise holes.
• Commonly used for making holes of various depths and diameters.

Broaching

• Uses a toothed tool (broach) to create complex internal shapes like splines and keyways.
• Suitable for applications requiring high precision and repeatability.

Grinding

• Uses an abrasive wheel to refine the surface finish and achieve tight tolerances.
• Often used in medical, aerospace, and precision engineering

Electrical Discharge Machining (EDM)

• Uses electrical sparks to erode material from a workpiece.
• Suitable for hard metals and intricate designs.

Laser Cutting

• A high-energy laser beam cuts through metal or plastic with extreme precision.
• Frequently used in electronics, aerospace, and automotive

Ultrasonic Machining

• Vibrating ultrasonic waves combined with an abrasive slurry remove material.
• Used for machining brittle materials like ceramics, glass, and composites.

Advantages of Machined Parts

Machined parts offer several advantages over other manufacturing methods like 3D printing or injection molding:

High Precision and Accuracy

• Capable of tolerances as tight as ±0.001 mm.
• Ensures perfect fit and function in critical applications.

No Minimum Order Quantity (MOQ)

• Unlike molding, CNC machining allows for small-batch or one-off production.

Strength and Durability

• Machined parts are made from solid materials rather than layered or molded structures, making them stronger.

Faster Production

• CNC machining can produce complex parts quickly, reducing lead times.

Surface Finishing Options

• Machined parts offer smooth surfaces without visible layer lines, unlike 3D printing.

Easy Design Modifications

• Engineers can alter digital CAD designs at any stage, reducing waste and improving efficiency.

Design Principles for Machined Parts

Designing parts for CNC machining isn’t just about creating the perfect shape—it’s about making sure the part is strong, cost-effective, and easy to manufacture. A well-designed part will save time, reduce costs, and improve performance. If a design is too complex, it may take longer to machine, require special tools, or even be impossible to produce.

Here are practical and easy-to-follow design tips to help you get the best results from CNC machining.

Keep Wall Thickness Balanced

Thin walls can cause vibrations, warping, and breakage during machining, making them harder to cut accurately. Thicker walls make parts stronger and more stable.

✅ Ideal wall thickness:

• Metals: At least 8 mm
• Plastics: At least 5 mm (since plastics are softer and more flexible)

If your design must have thin walls, consider adding ribs or supports to prevent bending.

Avoid Unnecessary Undercuts

Undercuts are areas that standard cutting tools can’t reach, requiring special tools or multi-axis machining, which increases cost and time.

✅ How to fix it:

• Redesign the part to eliminate undercuts.
• Use standard tool sizes to simplify the machining.
• If undercuts are necessary, keep them between 3 to 40 mm to match common cutting tool sizes.

Design Holes and Cavities with the Right Proportions

Drilling deep holes or machining deep cavities can be tricky because the cutting tool can only go so far without bending.

✅ Best practices:

• Hole depth should be no more than 4 times the diameter(e.g., a 5 mm hole shouldn’t be deeper than 20 mm).
• For deep holes, consider step drilling(drilling in stages) to improve accuracy.
• Cavities shouldn’t be deeper than 4 times their width to avoid tool deflection.

Adding rounded corners inside cavities also helps because cutting tools are round and sharp internal edges are difficult to machine.

Use Standard Thread and Fastener Sizes

If your part needs screws or bolts, stick to standard thread sizes so off-the-shelf fasteners can be used. Custom threads or very fine threads take longer to machine and cost more.

✅ Threading guidelines:

• Thread depth should be no more than 3 times the hole diameter.
• Use metric or standard (UNC/UNF) thread sizes to avoid custom tooling costs.
• Consider helicoil inserts for added durability in soft materials like aluminum or plastic.

Avoid Very Tall, Thin Features (Protrusions)

If a part has tall, thin sections, they may bend or vibrate during machining, reducing accuracy.

✅ Best ratio:

• The height of a feature shouldn’t be more than 4 times its width.
• If you need taller features, add extra support or increase the base width.

Keep Tolerances Realistic

Tight tolerances (extremely precise measurements) take longer to machine and increase costs. Only use tight tolerances where necessary, like for parts that must fit together precisely.

✅ When to use tight tolerances:

• Mating surfaces that must fit together.
• High-speed or high-stress components.
• Aerospace, medical, and automotive parts that require extreme precision.

For general applications, a tolerance of ±0.1 mm is usually fine. Only specify tighter tolerances (e.g., ±0.01 mm) if absolutely necessary.

Consider the Machine’s Capabilities

Not all CNC machines can handle very large, tiny, or complex shapes.

✅ Size guidelines:

• Standard CNC milling machines handle parts up to 400 x 350 x 150 mm.
• CNC turning machines can handle parts up to Ø 500 mm x mm.
• If your part is larger, discuss options with your manufacturer.

Reduce Tool Changes to Speed Up Production

The more times a machine needs to switch tools, the longer production takes. Design your part so it can be machined using as few different cutting tools as possible.

✅ Best practices:

• Stick to common drill and mill sizes(e.g., 6 mm, 8 mm, 10 mm).
• Use consistent hole diameters across your design.
• Avoid deep pockets that require longer cutting tools, as they are harder to machine accurately.

Choose Materials That Are Easy to Machine

Some materials wear out tools faster or require special cutting techniques, increasing machining costs.

✅ Best materials for easy machining:

• Aluminum – Lightweight, strong, and easy to cut.
• Brass– Very machinable and has great electrical conductivity.
• Delrin (POM)– A strong plastic with low friction and good wear resistance.