Twist drill nomenclature: identify the helix angle vs point angle Evaluate the statement about a twist drill: “The angle included between the two lips, projected on a plane parallel to the drill axis and parallel to the two cutting lips, is called the helix angle.” Decide if this statement is correct or incorrect.
Mechanical Engineering
Production Engineering
Difficulty: Easy
Choose an option
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ACorrect — that defines the helix angle
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BIncorrect — that is the point angle; helix angle is between flute helix and axis
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CCorrect only for drills above 20 mm diameter
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DIndeterminate without the chisel edge angle
Answer
Correct Answer: Incorrect — that is the point angle; helix angle is between flute helix and axis
Explanation
DefinitionsPoint angle: included angle between the two cutting lips (commonly ~118° for general-purpose drills).Helix angle: angle between the direction of the helical flute and the drill axis (commonly ~25°–35°).
ConclusionThe statement given defines the point angle, not the helix angle.
Final AnswerIncorrect — that is the point angle; helix angle is between flute helix and axis.