Flat (spade) drill geometry The cutting (point) angle commonly used on a flat drill generally varies over which range?

Introduction / Context:
The cutting angle (often called the point angle) of a drill strongly influences cutting forces, chip formation, and guidance. Flat or spade-type drills use relatively large point angles to provide strength at the cutting edge and to accommodate a variety of materials.

Given Data / Assumptions:

• Flat (spade) drill used for general-purpose drilling.
• Conventional practice for steels and nonferrous alloys.
• Normal shop grinding without special-purpose geometry.

Concept / Approach:
Point angle increases tool strength and changes thrust vs. torque balance. Spade drills typically employ a relatively obtuse angle, commonly around 90° to roughly 118°, extending to as high as 120° for specific applications, balancing chisel-edge length and lip loading.

Step-by-Step Solution:
Identify realistic ranges used in practice for spade drills.Exclude very small angles (3°–30°) as these are for rake/clearance, not point angles.Select the wide, commonly adopted range covering 90° to about 120°.

Verification / Alternative check:
Tooling catalogs list recommended point angles near 90°–118° for spade drills, with 118° a common standard similar to twist drills for many materials.

Why Other Options Are Wrong:
3°–8° and 20°–30° are not point angles; they resemble clearance/relief angle values. 60°–90° is too acute for most spade drilling in metals. 130°–150° is reserved for very hard or special materials and is not the general flat drill recommendation.

Common Pitfalls:
Confusing point angle with rake or clearance; using an overly acute angle causes weak lips and high thrust, while overly obtuse angles may increase rubbing at low feeds.

Final Answer:
90° to 120°