What does the "thrust angle" refer to?

The "thrust angle" refers specifically to the angle at which a cutting tool engages the workpiece. This angle is significant as it affects how the tool interacts with the material being machined. A proper thrust angle can enhance cutting efficiency, influence the quality of the finished surface, and reduce tool wear. It correlates with the direction of force applied during the cutting operation, ensuring that the tool penetrates the material effectively.

In contrast, the other options describe different aspects of machining. Tool wear relates to how the cutting edges degrade over time, the machine bed's angle pertains to the setup and stability of the machine, and the spindle rotation angle is tied to the tool's spinning motion rather than its engagement with the workpiece. Thus, the thrust angle is crucial for optimizing the cutting process and achieving desirable machining results.