In less than 15 minutes, you will learn all you need to know to design parts optimized for CNC machining: from Design for Machinability rules to cost reduction tips and from material selection guidelines to surface finishing recommendations.

CNC machining design restrictions

The design restrictions in CNC machining are a natural result of the mechanics of the cutting process and in particular:

Tool geometry

Most CNC machining cutting tools have a cylindrical shape with a flat or spherical end, restricting the part geometries that can be produced.

For instance, the internal vertical corners of a CNC part will always have a radius, no matter how small a cutting tool is used.

Tool access

Surfaces that cannot be reached by the cutting tool, cannot be CNC machined.

This prohibits, for example, the fabrication of parts with internal 'hidden' geometries, and puts a limit to the maximum depth of an undercut.

Workpiece stiffness

Tool stiffness

Like the workpiece, the cutting tool can also deflect or vibrate during machining. This results in looser tolerances and even tool breakage.

The effect becomes more prominent when the ratio of length-to-diameter of the cutting tool increases and is the reason why deep cavities cannot be easily CNC machined.

Workholding

The geometry of a part determines the way it will be held on the CNC machine and the number of setups required. This has an impact on the cost, but also the accuracy of a part.

For example, manual repositioning introduces a small, but not negligible, positional error. This a key benefit of 5-axis versus 3-axis CNC machining.