Manufacturing And Production Technology MCQ Questions & Answers | Mechanical Engineering

The correct option is "Zero rake angle" (Option A).

Reason: In thread cutting, accuracy of the thread form is critical. A zero rake angle preserves the true geometry of the thread profile and avoids distortion during cutting.

Why not positive rake? Although it reduces cutting forces in general machining, it changes the effective cutting geometry in threading and can distort the thread form.

Why not negative rake? It increases cutting forces and is unnecessary for precision thread cutting, potentially harming surface finish and tool life.

About point angle: The point (included) angle defines thread geometry (e.g., 60° for metric/UN), but it is a different parameter and not the ideal rake requirement.

Conclusion: For single point thread cutting tools, use zero rake angle to maintain accurate thread profile and dimensional correctness.

When a boring tool is set above the center height, it changes the angles at which the tool interacts with the workpiece.
Imagine the tool is slightly "tilted up".
Rake Angle:
The rake angle is the angle at which the cutting face of the tool meets the workpiece.
If the tool is tilted upwards (above center), the effective rake angle decreases.
Think of it as the tool becoming less "sharp" for cutting.
Clearance Angle:
The clearance angle is the angle between the flank of the tool and the finished surface of the workpiece.
This angle prevents the flank from rubbing against the workpiece.
If the tool is tilted upwards, the effective clearance angle increases.
This provides more space to avoid rubbing.
Conclusion:
Therefore, setting a boring tool above center height leads to a decrease in the effective rake angle and an increase in the effective clearance angle.
So, the correct answer is Option C.