Posted May 4, 2021

How To Optimize a Design for CNC Milling and Turning

A CNC lathe fabricates a design optimized for manufacturing

When designing a new part to be manufactured, there are many factors to keep in mind for the project’s success. Companies expect a new part to perform as designed and manufacture as efficiently as possible to keep production costs optimal. To achieve this, designers need to optimize digital models for the CNC mills and lathes to machine the part.

Every part has features essential to its operation, but other aspects of the design may need simplification or omission. In some cases, designers include unnecessary features and geometries out of habit or because they didn’t realize how it would impact the complexity of production. This article will look closer at problems like these and how part designers can streamline manufacturing by optimizing the design for CNC milling and turning.

Potential Design Problems

CNC machines create a wide range of parts, from plastic toys to aircraft landing gear components. Companies use CNC machining for manufacturing because it allows them to create complex geometries and shapes with pinpoint precision. However, the different machines and tools have some limitations, which can surprise designers if they don’t prepare.


  • CNC milling tools have a cylindrical design like drill bits, and their shape can restrict the geometries they create. Designers using large tools to create sharp corners may get design for manufacturability (DFM) feedback that the feature, as designed, is not manufacturable. 
  • Milling tools also have limits to depth and direction when machining a part. A designer that creates an overly complex internal geometry may get their part flagged with a DFM error. 
  • The cutting tools of CNC lathes can only operate within a specific range of motion. For parts with more complex geometries, a machine shop will use a lathe with live tooling or multiple machining operations.

To avoid problems like these, optimize designs for more efficient manufacturing. 

Seven Keys to Optimize a Design for CNC Milling and Turning

Designers should consider these seven points to ensure that a design has optimal compatibility with CNC mills and lathes before submitting it for manufacturing:

Consolidate your tools and workpiece setup

Production slows every time a CNC machine requires a new tool or a machinist must reposition a workpiece within the workholding or mill. Although this extra time may not appear problematic when producing a limited run of the part for prototyping, it can end up costing a lot of time and money during mass production. 

Limit the cavity depth

Designers should restrict the depth of cavities to four times the diameter of the cutting tool. The greater the depth, the more required time and cost for special tools or more expensive processes.

Avoid sharp-angled internal corners

Milling tools will leave a rounded corner in cavities equal to the diameter of the tool. Smaller tools can reduce these diameters, but that increases the time required for machining. For manufacturing efficiency, it is better to design rounded internal corners with bigger radii to minimize tool changes.

Use standard tolerances as much as possible

It is best to limit the number of tight tolerances on a design and only specify those required for critical features. Each unique tolerance specified in the design will increase the time and cost of manufacturing.

Consolidate holes with standard sizes

Non-standard features, such as holes less than 2.5mm in diameter, will increase the amount of time needed to fabricate the part. When possible, it is ideal to use standard size holes to reduce time and cost in your design (unless the non-standard features are necessary).

When possible, avoid thin walls

To avoid vibration and integrity problems with the part during machining, avoid cavities separated by thin walls. Metal walls thinner than 0.8mm, or 1.5mm for plastic, machine at slower speeds, reducing accuracy and increasing production time.

Keep tapped holes shallow

Machine shops find tapped holes challenging, so designers should minimize their use. When tapped holes are required, keep their thread length to a minimum. A bolt only needs three turns to hold it securely, and to go any deeper puts the tap at a greater risk of breaking during machining.

You can also help optimize a design for CNC milling and turning by choosing your materials wisely. The material characteristics, such as hardness and weight, need to be balanced against its machinability. For instance, a machine shop can cut aluminum much faster than harder metals, making it a more efficient choice. However, aluminum may not be the best choice based on the part’s application.

A certified machine shop can advise on design decisions and optimize the part for CNC machining.

What You Can Expect from Your Machine Shop to Help with Design Optimization

The CNC machine shop wants designs to be successful just as much as their customers. They help with design optimization using both automated tools and manufacturing expertise:

  • DFM Feedback: Reputable machine shops will provide you with Design For Manufacturability feedback that highlights any problem areas of your part that will be difficult to manufacture. Working in consultation with your vendor helps you make better decisions to balance your design priorities against manufacturing costs.
  • Online part ordering systems: Many machine shops now use an online part request system for their customers. Customers upload a CAD model to the evaluation system, which will provide immediate feedback on the part’s manufacturability. The customer can make changes if the shop discovers problems with the design, or if the part is acceptable, complete the order. This method saves a lot of time from older and more traditional paper-trail part request processes. Additionally, the automated evaluation system will point out problems that designers can correct before submitting a part for production.
  • Engineering representatives: Some machine shops use sales reps with engineering knowledge to help their customers make the best design choices. You can optimize your design by getting pivotal questions answered before submitting your part for production, from material selections to documentation requirements.

At Plethora, our goal is the successful manufacturing of your part. To that end, we want to work with you to optimize a design for the most efficient CNC machining possible. Our automatic DFM software combined with the online part request system will give you immediate answers. For more in-depth questions, our trained representatives are ready to provide any information you need. Our online systems are standing by to receive your data to begin working with you on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.

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Topics: materials, processes, Manufacturing, finishing, CNC machining, Quality, Prototyping, threading

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