Tool access is one of the main design limitations in CNC machining. To reach all surfaces of the model, the workpiece has to be rotated multiple times.
Whenever the workpiece is rotated, the machine has to be recalibrated and a new coordinate system has to be defined.
While designing, it is important to consider machine setups for two reasons:
The total number of machine setups affects the cost. Rotating and realigning the part requires manual work and increases total machining time. This is often acceptable if the part needs to be rotated up to three or four times, but anything above this limit is excessive.
To achieve maximum relative positional accuracy, two features must be machined in the same setup. This is because the new calibration step introduces a small (but non-negligible) error.
A 5-axis CNC machine moves cutting tools or parts along five axes at the same time. Multi-axis CNC machining can manufacture parts with complex geometries, as they offer two additional rotational axes. These machines eliminate the need for multiple machine setups.
Five-axis CNC machining allows the tool to remain constantly tangential to the cutting surface. The tool paths can be more intricate and efficient, resulting in parts with better surface finish and lower machining times.
That said, 5-axis CNC has its limitations. Basic tool geometry and tool access limitations still apply (for example, parts with internal geometries cannot be machined). Moreover, the cost of using such systems is higher.
Undercuts are features that cannot be machined using standard cutting tools, as some of their surfaces are not accessible directly from above.
There are two main types of undercuts: T-slots and dovetails. Undercuts can be one-sided or double-sided and are machined using special tools.
T-slot cutting tools are made of a horizontal cutting blade attached to a vertical shaft. The width of an undercut can vary between 3mm and 40mm. We recommend using standard sizes for the width (i.e. whole millimeter increments or standard inch fractions), as it is more likely that an appropriate tool is already available.
For dovetail cutting tools, the angle is the defining feature size. Both 45- and 60-degree dovetail tools are considered standard. Tools with an angle of 5-, 10- and up to 120-degree (at 10 degree increments) also exist but are less commonly used.
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