Essential Design Guidelines For CNC Machining

July 2, 2024


CNC machining has revolutionized manufacturing, enabling precise, intricate designs across various industries. However, in order to harness it’s full potential; a solid grasp of CNC-specific design principles are critical. Whether you're a seasoned engineer or just getting started with CNC machining, getting a grip on these guidelines is your ticket to creating efficient, cost-friendly, and easily manufacturable designs.

In this blog, we will be diving into some things you should look out for to ensure that your design is efficient, cost-effective and ready to be machined!

1. Deep Pockets

Deep holes and pockets could cause issues that affects the finish and precision of your part or even cause tool breakage. Such features also often require several cuts to be machined properly, which increases machining time, consequently increasing the cost of your part.

Rule of thumb:

Deep Pockets & Holes

  • If diameter of hole/smallest cutting tool required is <2mm, maximum recommended depth is 3x diameter of hole/smallest cutting tool required
  • If diameter of hole/smallest cutting tool required is >2mm, maximum recommended depth is 5x diameter of hole/smallest cutting tool required

2. Narrow Regions

Having narrow regions (tight gaps between features) that are deep limit the tool sizes that can be used, forcing manufacturers to use long, small diameter tools which are more prone to chatter and breakage. This not only increases machining time but also reduces part quality.

Thus keep the gap of narrow regions (gap between features) to no less than 3x the diameter of the smallest cutting tool used and minimize the depth of such features. the

3. Sharp Internal Features

As CNC endmills are circular, it’s resulting cut will leave behind a radius making sharp internal corners difficult to produce without using other more costly methods.

To avoid increasing the tooling cost of your part, opt for internal fillets or “dog bones” instead and stay away from sharp internal corners.

Example of using “dog bones” to avoid sharp internal corners.

4. Thin Walls

Thin walls can be tricky to machine as they are more prone to vibrations, lowering the achievable accuracy. Maintaining an appropriate wall thickness is crucial to ensure structural integrity, manufacturability, and cost-effectiveness.

Here are the general guidelines to follow:


  • Recommended Minimum Wall Thickness: 0.8mm
  • Absolute Minimum Wall Thickness: <0.5mm
    • If necessary a wall thickness of 0.5mm is possible, but it may lead to higher machining costs and potential issues with part strength and stability, thus it is not advisable.


  • Recommended Minimum Wall Thickness: 1.5mm
    • As plastic is more susceptible to warping and softening a higher wall thickness is recommended to avoid complications during machining.

5. Chamfers > Fillets

Creating outside fillets generally require more machine time and special tools which can unnecessarily drive up the cost of your part.

Choosing chamfers over fillets whenever possible can help guarantee a cost efficient design.

6. Inaccessible Features

CNC machines perform cutting operations by positioning the cutting tools above the workpiece and applying them downward, this makes it difficult for features hidden from the top angle to be machined. The only exception to this are undercuts which use a cutting tool which can cut cavities horizontally.

Thus it is important to ensure a cutting tool is able to access to all features within a part without being blocked while designing your part to prevent going back to the drawing board!

7. Tolerances

Tolerances are measurements signifying the level/variation of precision needed for your part. CNC machines are capable of achieving very high levels of accuracy, as high as 0.002mm. But such precision requires more machining time, increasing the cost of your part.

Hence, if precision isn't absolutely essential for your part, stick to general tolerances such as Factorem’s ISO 2768 wherever possible to avoid unnecessarily driving up your part’s costs.


Applying these brief guidelines in your design process will allow you to fully utilize CNC machining’s unique abilities and avoid possible hiccups, all while maximizing your component’s cost efficiency.

Lastly, remember that while these guidelines provide a great starting point, they are not exhaustive. Each CNC machining project is unique and may require additional considerations based on its specific requirements. Therefore, continuous learning and adaptation are key to mastering the art of CNC machining design.

Thank you for reading! I hope you’ve learnt something useful, check out some of our other articles here at Factorem and follow us on our journey to #HelpMakersMake!