Flat (spade) drill geometry For a flat drill used on metals, the typical relief (clearance) angle provided at the cutting edge is in which range?

Introduction / Context:
Relief (clearance) angle prevents rubbing of the flank behind the cutting edge and influences cutting forces, heat generation, and edge strength. Flat (spade) drills have simpler geometry than twist drills but still require carefully chosen relief.

Given Data / Assumptions:

• General-purpose drilling of steels and non-ferrous alloys with a flat drill.
• Balanced need: avoid rubbing while maintaining edge strength.

Concept / Approach:
Too small a relief angle causes rubbing and heat; too large weakens the edge and increases chipping risk. Practical shop recommendations position flat drill relief in a modest range sufficient to clear the flank without undermining strength—typically a few degrees.

Step-by-Step Solution:
Assess functional need: reduce contact behind the cutting edge.Select moderate relief to balance sharpness and strength.Adopt the standard range 3°–8° as suitable for metal cutting.

Verification / Alternative check:
Toolroom guides and handbooks specify small relief angles for spade/flat drills; larger angles are reserved for very soft materials or special geometries.

Why Other Options Are Wrong:

• 20°–30° (B) is excessive for general metal drilling and weakens the edge.
• 60°–90° (C) and 90°–120° (D) are unrealistic for relief; these are in the range of point or included angles, not clearance.
• 0°–2° (E) risks severe rubbing and overheating.

Common Pitfalls:
Confusing point angle with relief angle; over-grinding relief leading to rapid chipping; ignoring material-specific tweaks.

Final Answer:
3° to 8°