Drilling fundamentals: A 20 mm diameter drill runs at 500 r.p.m. with a feed of 0.2 mm/rev to make a through-hole in a 20 mm thick mild-steel plate. What is the depth of cut in this drilling operation?

Introduction / Context:
In drilling, several quantities are defined differently than in turning. The term “depth of cut” in drilling is a geometric measure defined by convention and does not refer to plate thickness or feed. This question tests correct identification of the drilling depth of cut.

Given Data / Assumptions:

• Drill diameter, D = 20 mm.
• Rotational speed, N = 500 r.p.m. (not required for depth of cut).
• Feed, f = 0.2 mm/rev (not required for depth of cut definition).
• Plate thickness = 20 mm (this is the drilling depth, not the “depth of cut”).

Concept / Approach:
By standard machining terminology, for drilling: depth of cut (t) = D/2. The rationale is that each cutting lip removes material equivalent to a radial engagement equal to half the drill diameter. The feed per revolution relates to chip thickness per lip, while the plate thickness relates to the axial drilling depth, not the depth of cut.

Step-by-Step Solution:

Verification / Alternative check:
If asked for material removal rate, one would use feed and speed; here, only the geometrical convention for drilling depth of cut is needed.

Why Other Options Are Wrong:

• 0.2 mm: this is the feed per revolution, not depth of cut.
• 20 mm: this is the plate thickness (axial depth), not the drilling depth of cut.
• 100 mm: unrelated numerical distractor.

Common Pitfalls:
Confusing axial drilling depth with depth of cut; mixing feed with depth of cut definition.

Final Answer:
10 mm