How to design parts for CNC machining

To take advantage of the capabilities of CNC machining to the fullest, a designer must follow certain Design for Manufacturing rules. This can be challenging though, as specific industry-wide standards do not exist.Get more news about Desktop Cnc Machine Parts,you can vist our website!

In this article, we compiled comprehensive guidelines with the best design practices for CNC machining. We asked for feedback from industry experts and CNC machining service providers to compile an extensive list of up-to-date information.

We focused on describing what is feasible with modern CNC systems, neglecting the associated cost. For a guide on designing cost-effective parts for CNC, please refer to this article.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.
CNC offers great design flexibility, but certain design restrictions exist. These restrictions are related to the basic mechanics of the cutting process and are related mainly to 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 the material is removed from the workpiece, the geometry of the tool is transferred to the machined part. This means, for example, that the internal corners of a CNC part will 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 this way, cannot be CNC machined.

There is an exception to this rule: undercuts. We will see how you can use undercuts in your designs in latter section.

A good design practice is to align all features of your model (holes, cavities, vertical walls etc) to one of the 6 main principal directions. See this rule as a recommendation and not a restriction though, as 5-axis CNC systems offer advanced workpiece holding capabilities.

Tool access is also an issue when machining features with large depth to width ratio. To reach the bottom of a deep cavity, for example, special tools with long shafts are required. This lowers the stiffness of the end effector, increasing the vibrations and lowering the achievable accuracy.