Difficulty: Easy
Correct Answer: 118°
Explanation:
Introduction / Context:
The point angle of a twist drill affects chisel edge length, thrust force, chip flow, and wear. A widely adopted standard exists for general-purpose drilling in steels and many other materials.
Given Data / Assumptions:
Concept / Approach:
The most common point angle is 118°. It balances penetration and edge strength, producing reasonable thrust while allowing acceptable chip evacuation in many materials. Harder materials or specific applications may use 135° or other angles, but 118° remains the general baseline.
Step-by-Step Solution:
Identify general standard → 118°.Note variants (e.g., 135° split point) for tough materials, but that is not the “usual” case.Answer: 118°.
Verification / Alternative check:
Drill manufacturer catalogs and handbooks list 118° as the default point angle for general-purpose drills.
Why Other Options Are Wrong:
70° and 100° are too small, increasing thrust and weakening lips; 130° or 150° are more specialized for hard alloys and reduce wandering but are not the default standard.
Common Pitfalls:
Confusing point angle with lip relief or helix angle; assuming one angle fits all materials without considering modifications.
Final Answer:
118°
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