Custom Machining: What is It and Why Do You Need It for Your ...

The global machining market is now worth so much, with conventional machining holding 30% and precision machining taking the remaining 70%. Custom machining is the order of the day, making it more straightforward to order customized components from machine shops.

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If you’re not implementing custom machining for your business yet, you could be giving your competitors a significant advantage over you. But what is custom machining, and why is it so important for your business? 

In this article, we will cover all the different aspects of custom machining, including its incredible benefits for your business performance.

What is Custom Machining?

Custom machining entails every different form of CNC machining. It refers to ordering CNC machining services to meet specific requirements for various parts. This means that the purpose for choosing custom machining is to create components that meet your business goals and do not exist elsewhere.

So, custom machining is the best option if you have a completely new idea or invention or need your parts in nonstandard sizes. With this process, setup times are very short so that quality components can be made very fast from 3D CAD models. It also rarely involves minimum order quantity.

Types of Custom Machining Services

Custom machining involves several manufacturing techniques, ranging from 5-axis CNC machining to metal forming. The best machining services use machines that turn, mill, drill, or last cut these techniques.

CNC Milling

Milling uses a rotating device to remove and cut chips from the workpiece through physical contact. 

Milling technology finds use in various purposes like chamfering, slotting, and threading. It allows for the fabrication of intricate and complex designs. The accuracy of CNC milling is matchless with tolerances of +/-0.01mm.

There are different sub-types under CNC machining services, such as gear milling, surface milling, and form milling. The various milling processes can be used on metals like aluminum, plastic, and steel.

CNC Turning or Lathing

CNC turning or lathing is used for the fabrication of a cylindrical path like bushing or shaft.  The performance of the CNC equipment helps it to controls the cutting tool to and fro and axially along the side while the metal part spins.

The material around the metal is removed, thereby producing the desired shape and diameter. Turning can be done with a fixed or sliding head CNC machine. The latter is used in reducing the final production time and price.

CNC Multi-Spindle Machine

CNC multi-spindle machine has a lot of spindles placed in a drum. This drum changes its position, rotates horizontally, and finishes many operations simultaneously without multiple spindles.

This divides the work; one operation would have to be carried out after the other to complete the product of choice.

With every drum rotation, a part of the fabrication is completed. Multi-spindle makes CNC machining more efficient and cost-effective than multiple equipment.

CNC Laser Cutting

This manufacturing technique involves the use of laser beams to melt, vaporize, or remove the material. CNC laser cutting often employs optics, a guidance system, and an assist gas to direct the laser beam onto the workpiece.

After electrically exciting the laser, the beam reflects and amplifies with a partial mirror. Once there is enough energy, the laser beam is focused on the workpiece.

CNC laser cutting is faster, it involves lesser waste, and it is ideal for an extensive range of materials for quality production.

CNC Drilling

CNC drilling produces cylindrical holes in a workpiece using multi-point drill bits. Perpendicular and angular hole drilling can be achieved using this method. Perpendicular drilling means inserting the rotatory drill in the workpiece with the aid of a CNC machine.

Angular drilling could be complicated; it uses clamping devices and specialized machine configurations. A few operations performed with CNC drilling are reaming, countersinking, and tapping.

Electric Discharge Machining (EDM)

These are non-mechanical forms of material remover that uses erosive chemical or parts.

Electric discharge machining uses spark transmitted through a dielectric fluid from an electrode to a surface of a conductive workpiece. This method can machine fine features, including di cavities, diameter holes, etc. 

The discharge rate is generally not determined by hardness but by the conductivity of the metal, thermal energy.

Some manufacturers and engineers use sinking, wire erosion, spark eroding to describe electrical discharge machining [EDM]. EDM process does not use mechanical force.

Why Do You Need Custom Machining for Your Business?

Whether it is plastic machining or metal machining of aluminum, steel, brass, etc., custom machining has all the capabilities and benefits of on-demand machining and more. Different industries such as aerospace, automotive, consumer electronics, defence, and others benefits from piece parts from custom machining. Some of its benefits include:

High Precision and High-Quality Custom Machined Parts

Custom machining enables the seamless production of complex applications. CNC production offers you incredibly high precision, even with unique features and tight tolerances.

CNC machines also consistently and continuously produce similar parts until you get the last piece of your order. 

Increased Productivity and Efficiency

CNC machines can now carry out takes throughout the day without slowing down. They use computer programs and instructions to perform, eliminating the possibilities of human error.

At the same time, they also guarantee consistent results from the production.

Timely Production

CNC machining is a subtractive process. It involves removing parts of the role metals to achieve the desired product. The computer control in CNC machines ensures speed maintenance at set limits.

This way, it is almost impossible to encounter errors. Moreover, provided there are experts engineers, you can be sure of faster completion of projects. This translates to faster time delivery.

Affordability and Higher Profits

Since custom machining involves products’ unique design, you will not have to spend more than you should.

At the same time, you tend to get high-quality products. All of this translates to higher profits in the long run.

When Do You Need A Custom Machining Company?

Custom machining often comes in handy whenever you need to do one or more of the following:

Fabricate New Parts with Special Requirements 

Custom machining will help you with projects requiring additional parts, human resources, and supplies to complete.

If you need to create unique “made-to-order” parts that are not on the manufacturer’s catalog, you can be sure of improved and smooth running with quality custom Machining services. 

Replace Obsolete or Discontinued Parts

Manufacturers can use this process to modify existing parts that may be obsolete into ones that fit your purpose.

Custom Machining can reverse engineering works to recreate custom machined parts that you may not find elsewhere.

Work with Difficult Materials

Specialized CNC equipment includes machinery and parts that can carry out complex processes. If you need to use tough metals like titanium alloy, stainless steel, Steel etc., custom machining gives you the expected results. 

Others

Other reasons for choosing custom machining include:

• Low volume production 
• The need to combine multiple elements into one part
• Emergency parts development

Why You Should Choose Us As Your Custom Machining Company

Here are the benefits of choosing AT Machining for your quality applications:

Guaranteed Quality

Our company is ISO certified, and we boast of experienced and professional engineers to ensure quality services. The raw materials we use for our CNC machining services are of the highest quality, translating to quality end products.

Instant Quoting 

As soon as you upload your 2D or 3D CAD files on our platform, we will analyze the file and list the pricing within a few hours. This quick quote speeds up the manufacturing process for faster time delivery.

Material Certification 

AT Machining is a rights reserved powered company that ensures excellence. We give customers traceable information on the features of every material we use for your machined parts through adequate certification. Quality is our watchword! 

Dimensional Report

Custom machined parts should come in the right measurements. We ensure this and also provide details of the dimensions of your products. This way, our customers can be sure of the right custom machined parts for specific applications.

Conclusion

Custom machining is taking over the rapid prototyping industry, giving you several benefits throughout product development. Its applications are prevalent in aerospace, automotive, medical, consumer electronics, and many other industries to create quality custom machined parts.

There are a few easy steps you can take to optimize your designs for computer numerical control (CNC) machining. By following design-for-manufacturing (DFM) rules, you can get more out of CNC machining's broad capabilities. This can be challenging though, as industry-wide specific standards do not exist.

In this article, we offer a comprehensive guide to the best design practices for CNC machining. To compile this extensive up-to-date information, we asked for feedback from industry experts and CNC machining service providers. If you are optimizing for costs, check out this guide to designing cost-effective parts for CNC.

What is the CNC machining process?

CNC machining is a subtractive manufacturing technology. In CNC, material is removed from a solid block using a variety of cutting tools that rotate at high speed—thousands of RPM—to produce a part based on a CAD model. Both metals and plastics can be CNC machined.

CNC-machined parts have high dimensional accuracy and tight tolerances. CNC is suitable for both high-volume production and one-off jobs. In fact, CNC machining is currently the most cost-effective way of producing metal prototypes, even compared to 3D printing.

Read our introduction to the basic principle of CNC machining.

What are the main restrictions of CNC design?

CNC offers great design flexibility, but there are a few restrictions. These limitations relate to the basic mechanics of the cutting process and mainly concern tool geometry and tool access.

Tool geometry

Most common CNC cutting tools (end mill tools and drills) have a cylindrical shape and a limited cutting length. 

As material is removed from the workpiece, the geometry of the tool is transferred to a machined part. This means, for example, that the internal corners of a CNC part always have a radius, no matter how small a cutting tool was used.

Tool access

To remove material, the cutting tool approaches the workpiece directly from above. Features that cannot be accessed in this way cannot be CNC machined.

There is an exception to this rule: undercuts. There’s a section on undercuts towards the end of this article.

We recommend aligning all your model’s features (holes, cavities, vertical walls, etc.) to one of the six principal directions. However, see this rule as a recommendation and not a restriction, as 5-axis CNC systems offer advanced workpiece-holding capabilities.

Tool access is also an issue when machining features with a large depth-to-width ratio. To reach the bottom of a deep cavity, for example, you need tools with extended reach. This means a wider range of motion for the end effector, which increases the machine chatter and lowers the achievable accuracy.

It will simplify production if you design parts that can be CNC machined with the tool that has the largest possible diameter and the shortest possible length.

CNC design guidelines

A challenge that frequently comes up while designing a part for CNC machining is that no industry-wide specific standards exist. CNC machine and tool manufacturers continuously improve the technology’s capabilities, expanding the limits of what is possible. The table below summarizes recommended and feasible values for the most common features encountered in CNC machined parts. 

Cavities and pockets

Illustration of cavities and pockets

Recommended cavity depth: 4 times cavity width

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End mill tools have a limited cutting length (typically 3–4 times their diameter). Tool deflection, chip evacuation and vibrations become more prominent when cavities have a smaller depth-to-width ratio.

Limiting the depth of the cavity to four times its width ensures good results.

If larger depths are required, consider designing parts with a variable cavity depth.

Deep cavity milling: Cavities with depths greater than six times the tool diameter are considered deep. A tool diameter-to-cavity depth ratio of up to 30:1 is possible using specialized tooling (maximum depth: 35 cm with a 1-inch diameter end mill tool).

Internal edges

Illustration of internal edges

Vertical corner radius

Recommended: ⅓ times cavity depth (or larger)

Using the recommended value for internal corner radii ensures that a suitable diameter tool can be used and aligns with guidelines for the recommended cavity depth.
Increasing the corner radii slightly above the recommended value (e.g. by 1 mm), allows the tool to cut following a circular path instead of a 90 angle. This is preferred as it results in a higher quality surface finish. If sharp 90-degree internal corners are required, consider adding a T-bone undercut instead of reducing the corner radius.

Floor radius

Recommended: 0.5  mm, 1  mm or no radius
Feasible: any radius

End mill tools have a flat or slightly rounded lower cutting edge. Other floor radii can be machined using ball end tools. It is good design practice to use the recommended values, as it is preferred by the machinists.

Thin walls

Minimum wall thickness

Recommended: 0.8 mm (metals), 1.5 mm (plastics)
Feasible: 0.5 mm (metals), 1.0 mm (plastics)

Decreasing the wall thickness reduces the stiffness of the material, which increases vibrations during machining and lowers the achievable accuracy. Plastics are prone to warping (due to residual stresses) and softening (due to temperature increase), so a larger minimum wall thickness is recommended. The feasible values stated above should be examined on a case-by-case basis.

Holes

Diameter

Recommended: standard drill bit
Feasible: any diameter larger than 1 mm

Holes are machined using either a drill bit or an end mill tool. The size of the drill bits is standardized (in metric and imperial units). Reamers and boring tools are used to finish holes that require tight tolerances. For high-accuracy holes with a diameter smaller than 20 mm, using a standard diameter is recommended.

Maximum depth

Recommended: 4 times nominal diameter
Typical: 10 times nominal diameter
Feasible: 40 times nominal diameter

Holes with a non-standard diameter must be machined with an end mill tool. In this case, the maximum cavity depth restrictions apply and the recommended maximum depth value should be used. Holes deeper than the typical value are machined using specialized drill bits (with a minimum diameter of 3mm). Blind holes machined with a drill have a conical floor (135-degree angle), while holes machined with an end mill tool are flat.
There is no particular preference between through holes or blind holes in CNC machining.

Threads

Illustration of threads

Thread size

Minimum: M1 (and lower, in some cases)
Recommended: M6 or larger

Threads are cut with taps and external threads with dies. Taps and dies can be used to cut threads down to M2. CNC threading tools are common and are preferred by machinists, as they limit the risk of tap breakage. CNC threading tools can be used to cut threads down to M6.

Thread length

Minimum: 1.5 times nominal diameter
Recommended: 3 times nominal diameter

The majority of the load applied to a thread is taken by the few first teeth (up to 1.5 times the nominal diameter). Threads longer than 3 times the nominal diameter are thus unnecessary.

For threads in blind holes cut with taps (i.e. all threads smaller than M6), add an unthreaded length equal to 1.5 times the nominal diameter at the bottom of the hole. When a CNC threading tool can be used (i.e. threads larger than M6), the hole can be threaded throughout its length.

Small features

Illustration of small CNC features

Minimum hole diameter

Recommended: 2.5 mm (0.1 inches.'')
Feasible: 0.05 mm (0.005 inches.'')

Most machine shops can accurately machine cavities and holes using tools down to 2.5 mm (0.1 inches) in diameter. Anything below this limit is considered micro-machining. Specialty tools (micro-drills) and expert knowledge are required to machine such features because the physics of the cutting process change with this scale. Unless absolutely necessary, the recommendation is therefore to avoid them.

Tolerances

CNC Tolerances illustration

Typical: +-0.1 mm
Feasible: +-0.02 mm

Our tolerances are either medium or fine. If tolerances are not specified, manufacturing partners will use the selected grade.
Tolerances define the boundaries for an acceptable dimension. The achievable tolerances vary according to the base dimension and the geometry of the part. The values above are reasonable guidelines.

Text and lettering

Recommended: font size 20 (or larger), 5 mm engraved

Engraved text is preferred over embossed text, as less material is removed. Using a minimum size of -20 sans -serif font (e.g. Arial or Verdana) is recommended. Many CNC machines have pre-programmed routines for these fonts.

CNC machine setups and parts orientation

Tool access is one of the main design limitations in CNC machining. To reach all surfaces of the model, the workpiece has to be rotated multiple times. 

Whenever the workpiece is rotated, the machine has to be recalibrated and a new coordinate system has to be defined.

While designing, it is important to consider machine setups for two reasons:

• The total number of machine setups affects the cost. Rotating and realigning the part requires manual work and increases total machining time. This is often acceptable if the part needs to be rotated up to three or four times, but anything above this limit is excessive.

• To achieve maximum relative positional accuracy, two features must be machined in the same setup. This is because the new calibration step introduces a small (but non-negligible) error.

What is 5-axis CNC machining?

A 5-axis CNC machine moves cutting tools or parts along five axes at the same time.  Multi-axis CNC machines can manufacture parts with complex geometries, as they offer two additional rotational axes. These machines eliminate the need for multiple machine setups.

What are the advantages and limitations of 5-axis CNC machining?

Five-axis CNC machining allows the tool to remain constantly tangential to the cutting surface. The tool paths can be more intricate and efficient, resulting in parts with better surface finish and lower machining times.

That said, 5-axis CNC has its limitations. Basic tool geometry and tool access limitations still apply (for example, parts with internal geometries cannot be machined). Moreover, the cost of using such systems is higher.

CNC machining undercuts

Undercuts are features that cannot be machined using standard cutting tools, as some of their surfaces are not accessible directly from above.

There are two main types of undercuts: T-slots and dovetails. Undercuts can be one-sided or double-sided and are machined using special tools.

T-slot cutting tools are made of a horizontal cutting blade attached to a vertical shaft. The width of an undercut can vary between 3mm and 40mm. We recommend using standard sizes for the width (i.e. whole millimeter increments or standard inch fractions), as it is more likely that an appropriate tool is already available. 

For dovetail cutting tools, the angle is the defining feature size. Both 45- and 60-degree dovetail tools are considered standard. Tools with an angle of 5-, 10- and up to 120-degree (at 10 degree increments) also exist but are less commonly used.

Undercut design for CNC machining

When designing parts with undercuts on internal walls, remember to add enough clearance for the tool. A good rule of thumb is to add space equal to at least four times the depth of the undercut between the machined wall and any other internal wall.

For standard tools, the typical ratio between the cutting diameter and the diameter of the shaft is 2:1, thereby limiting the cutting depth. When a non-standard undercut is required, it is common practice for machine shops to manufacture their own custom undercut tools. This can add to lead time and cost, so avoid it if possible.

Drafting a technical drawing

Technical drawings are sometimes used by engineers to communicate specific manufacturing requirements to the machinist. If you are interested in the topic, read this article about how, when and why to use technical drawings.

Uploading a technical drawing with your quote

We don’t usually require a technical drawing for orders on our platform, but in some cases, they can add valuable context to a quote request. Certain design specifications cannot be included in a STEP or IGES file. For example, you’ll have to include a 2D technical drawing if your model includes threaded holes or shafts and/or dimensions with tolerances tighter than the selected grade.

If you add a technical drawing, please make sure it matches the specifications of the files uploaded. If the technical drawings do not match the files uploaded or the quote specifications:

• The quote specifications are considered the point of reference for the technology, material and surface finishes.

• The technical drawings are considered the point of reference for the thread specifications, tolerance specifications, surface finish details, part marking requests and heat treatment specifications. 

• The CAD file is considered the point of reference for the part design, geometry, dimension and feature locations.

For further details, read our specifications policy.

What are the best practices for CNC machining?

• Design parts that can be machined using the tool with the largest possible diameter.

• Add the large fillets (at least ⅓ times the cavity depth) to all internal vertical corners.

• Limit the depth of cavities to 4 times their width.

• Align the main features of your design with one of the six principal directions. If that is not possible, 5-axis CNC machining is an option.

• Submit a technical drawing with your drawing if your design includes threads, tolerances, surface finish specifications or other notes for the machine operator.

Have parts you need CNC machined? Upload your designs and our DFM tool will suggest optimizations and provide instant pricing.