Why Tool Radius Changes Your CNC Design More Than You Think

One of the biggest differences between CAD geometry and CNC reality is the cutting tool.

In CAD, internal corners can be perfectly sharp.

But CNC milling tools are cylindrical.

That means every internal pocket naturally has a radius.

The smaller the corner radius you require, the smaller the tool diameter needs to be.

And smaller tools bring challenges:

• Lower cutting efficiency
• Higher risk of tool deflection
• Longer machining time
• More expensive manufacturing

This is why experienced designers often add corner reliefs or increase internal radii instead of forcing sharp corners.

For example:

A deep pocket with tiny internal corners may look simple in CAD, but machining it requires multiple tool changes and slower cutting parameters.

A slightly larger radius could allow a larger tool, reducing machining difficulty while maintaining the same functional purpose.

The goal is not to remove every radius.

The goal is to design a radius that matches the function.

Manufacturing-friendly geometry is often the result of understanding how the tool actually moves.

💬 Discussion:

When designing CNC pockets, do you usually prioritize the smallest possible radius or the easiest machining approach?

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