Design is a crucial aspect of the CNC manufacturing process. In addition to providing machining instructions, it directly impacts machining time, cost, and effort. This article explores 10 ways to improve your CNC machining design to increase machining efficiency and save cost.
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While CNC machining can produce highly complex geometries, certain features simply cannot be machined using conventional CNC machining. These features include:
CNC design mistakes: Complex internal channels
See our CNC machine design guide to learn more about designing for CNC machining.
While it should not come at the expense of functionality, simplicity reduces the time and cost of manufacturing. Designing unnecessary complex features is a common CNC design mistake. When designing a feature in a part or an assembly, consider the processes and tooling it would take to achieve that part. The design should satisfy all functional and structural requirements, with the aim of featuring features that do not require advanced 5-axis machining or Electrical discharge machining (EDM), as these cost more.
CNC machining is highly accurate and can achieve tight tolerances. However, in many instances, applying tolerance to all the dimensions in your design is unnecessary. Improve CNC design by only specifying tolerance when it is crucial for the part's functionality, such as mating or moving parts. CNC machining operations, such as CNC milling and CNC turning, typically apply a default tolerance of ± 0.13 mm, which is quite accurate. Tighter tolerances are achievable but require more time and effort. See our guide on CNC machining tolerances for more information on tolerancing.
CNC design mistakes: Over tolerancing
Improve your design by minimising aesthetic features. Considering the capabilities of CNC machining services, it may be tempting to get carried away with decorative patterns, embossments, engravings, lettering, and other aesthetic features. However, features that have no functionality and only serve to improve aesthetics unnecessarily increase machining time and effort, and including them is a major CNC design mistake. On the other hand, if aesthetics is a major consideration for your part, then feel free to include such features.
During machining, the workpiece is subject to continuous vibration on contact with the cutting tool. Similarly, the tool or workpiece may bend or deflect slightly. Thinner walls are less stiff and more susceptible to bending, breaking, and warping due to vibrations and deflections. Their susceptibility to vibrations also lowers achievable accuracies. Design sufficiently thick walls with enough stiffness to withstand vibration or tool deflection. We recommend a minimum wall thickness of 0.8 mm for metals and 0.15 mm for plastics.
Maintaining a good wall width-to-height ratio is also important, as taller walls are also more susceptible to damage and warping during machining. We recommend a width-to-height ratio of 3:1 for non-supported, free-standing walls to ensure stability.
Improve CNC design: Sufficient wall thickness
The cylindrical geometry of CNC milling cutting tools makes them unable to machine sharp internal edges. These tools produce a radial internal edge that is a minimum of the tools’ radii. Improve your CNC design by adding radii to internal edges. Another common CNC design mistake is adding an internal edge radius smaller than the tool’s radius. We recommend adding an internal radius 30% bigger than your cutting tool’s radius to mitigate tool wear and tear. For example, if your cutting tool is 10 mm, design internal edges with a 13 mm radius. This allowance reduces tool stress and increases cutting speed.
Improve CNC design: Assign Radii To Internal Edges
Standard hole sizes can be efficiently and accurately drilled with readily available standard drill bits. Non-standard holes, on the other hand, require end mill tools to machine out the dimension progressively. This increases machining time and effort. Furthermore, for threaded holes, standard hole sizes have corresponding thread sizes programmed in CNC machines, making it more efficient to create threaded holes.
CNC design mistakes: Non-standard hole sizes
The strength of thread connections usually resides in the first few threads. Improve your CNC design by limiting the depths of your threads to a maximum of three times the hole diameter. For through holes, you can design threads at the top and bottom. For blind holes, we recommend leaving an unthreaded length of half the hole’s diameter at the bottom.
Improve CNC design: Limith thread depth
CNC cutting tools have a limited depth, typically 3 to 4 times their diameter, beyond which they are highly susceptible to deflection and fracture. Design cavities with a suitable depth-to-width ratio to prevent tool hanging and deflection and to facilitate chip evacuation. Milling tools mill cavities three times their diameter in depth most efficiently. Cavities deeper than six times the tool diameter are considered deep. Such cavities should have a maximum depth of four times their width to allow for sufficient machining space.
Improve CNC design: Limit cavity depth
CNC machines typically produce a default surface roughness of 3.2 µm Ra and can produce surfaces as smooth as 0.06 µm Ra. However, machining time and cost increase exponentially with specified surface roughness. We recommend specifying the default surface roughness of 3.2 µm Ra when surface roughness is not critical. Smooth surface roughness is crucial for functionality in certain applications, such as load-bearing and mating, moving parts. For example, Medical CNC machining applications, such as joint replacement parts where loading and movement are continual, require very low surface roughness. See our CNC machining surface roughness article to learn more about specifying the right surface roughness for your part.
By avoiding these CNC design mistakes, you can significantly improve your design and optimise the CNC manufacturing process. At Geomiq, our instant quoting platform analyses your design in seconds, providing valuable DFM feedback. Upload your CNC design to get started and receive your part in as little as three days.
From vehicle brakes and engine parts to wooden furniture and aviation parts, computer numerical control (CNC) machines can create a wide variety of materials. Every item produced by a CNC machine is crafted with incredible precision so that it meets the required specifications for proper use.
While today’s CNC machines are incredibly complex, they can’t do all of this on their own. To run effectively and efficiently, they require the skills of a CNC machinist, who will load the program, set up the machine and monitor it to ensure everything works correctly.
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If this sounds like an exciting career path, consider enrolling in a training program. UTI’s CNC Machining Technology program, which is offered at the campus in Mooresville, North Carolina, can equip you with the skills to create performance parts and components from raw materials.1
Curious to learn more? Read along as we answer nine of the most common questions we receive about the CNC Machining Technology program. If you’re ready to get started and talk to an Admissions Representative, request information today.
UTI’s CNC program can be completed in just 36 weeks. Unlike traditional college programs that typically take four years to complete, this program is designed to have you on your way to pursuing a career in less than nine months.
While the time spent training is short, you’ll walk away with an in-depth understanding of the CNC industry and have hands-on skills you can start applying to a career. Your courses will cover a variety of topics, including:
To learn more about what you’ll learn in each individual class, check out our CNC course guide.
While certification is highly suggested and sometimes required for auto and diesel techs, this isn’t always the case in the CNC industry.
UTI doesn’t offer certifications through the CNC program, but we do follow most of the National Institute of Metalworking Skills’ guidelines to ensure students are learning what the industry requires. For students who choose to pursue certifications, they can do so after graduation and will have a foundation of skills that can be beneficial as they go through the process.
Students in the CNC Machining program train on Mastercam, a leading CAD/CAM software solution used in the industry. Instructors also teach students G-Coding directly into the machines, which they’ll use in the field.
Mastercam isn’t the only brand students will have exposure to in the program. UTI’s CNC program was created in conjunction with Roush Yates, a leading brand in the performance industry, to ensure the curriculum is aligned with industry expectations. Students will also have the chance to work with equipment from Mitee-Bite and Mitsubishi Materials.
Students in the CNC program mostly train on HAAS CNC machines. Throughout their coursework, they learn how to set up and operate manual machining equipment, as well as how to set up, operate and program CNC machining equipment.
Additionally, students learn to read blueprints, interpret Geometric Dimensioning and Tolerancing, inspect and measure parts, and perform required mathematical computations required of those in the machining industry. A key emphasis is placed on safety to ensure students are equipped to have long, successful careers in the field.
Read:6 of the Most Common CNC Machines
All of the tools students use while in the CNC machining program are provided by UTI, so they don’t need to purchase their own tools. However, students can use UTI’s Snap-on student discount when it comes time to build their tool set after graduation.
The CNC machining program is a general program designed to prepare students for career opportunities in the manufacturing industry. Students in the program don’t specifically learn to bore out engines and rebuild them, but the skills they learn can be applied in an automotive environment if they choose to take that route.
UTI is proud to offer Career Services resources. While in school, UTI’s team of local Career Advisors can assist students in their search for a part-time local job that doesn’t interfere with their studies.1 Many manufacturing jobs are full-time, but some students do work in industry jobs as they complete their training.
This team of Career Advisors is also available to students who are seeking employment after graduation. UTI has relationships with national dealerships, distributors and other employers of all sizes across the country to help identify potential jobs for graduates.
The CNC Machining Technology program teaches three axes. This helps to prepare students to pursue entry-level roles in the CNC industry after they graduate.
Read:What Are Machining Tolerances?
Cost is an important factor to consider when looking into any kind of training program. At UTI, there are several ways you may be able to save on your education, including financial aid, scholarships and grants.10
The Financial Aid team at UTI is available to answer any questions and assist you along the way, whether you need help filling out a FAFSA, taking out a loan or applying for scholarships. To determine your financial aid eligibility and out-of-pocket costs associated with going to UTI or any of its schools, use our Tuition Estimator (Net Price Calculator).
The CNC Machining Technology program starts every six weeks, so you’re able to get going and prepare for your career sooner. To learn more, visit our program page and request information to get in touch with an Admissions Representative today.
In the meantime, feel free to check out these additional resources:
For more information, please visit EDM Services.