Center drilling is used to create a small conical hole at the center of a workpiece to guide a lathe or machine center during turning or drilling.

Spot drilling is used to make a shallow depression that accurately marks the drill position and prevents the main drill from wandering.

center drilling supports the workpiece, while spot drilling guides the drill.

Center Drilling Vs Spot Drilling :

Here’s a detailed comparison of Center Drilling and Spot Drilling, which are often confused but serve different purposes in machining:

1. Definition

Center Drilling:
A process of making a small, conical hole at the center of a workpiece to guide a lathe or machine center for turning, drilling, or other operations.
Spot Drilling:
A shallow hole made to accurately mark or locate the position of a hole before drilling, ensuring the main drill does not wander.

2. Purpose

Center Drilling:
- Provides a starting point for turning or drilling.
- Supports the workpiece on a lathe center during machining.
Spot Drilling:
- Guides the main drill bit to the exact position.
- Prevents drill walking or slipping, especially on smooth surfaces.

3. Hole Shape

Center Drilling:
Produces a small, tapered conical hole (often with a flat tip).
Spot Drilling:
Produces a shallow depression, typically flat-bottomed or slightly angled, just enough to guide the drill.

4. Depth

Center Drilling:
Usually deeper than a spot drill to accommodate a lathe center tip.
Spot Drilling:
Very shallow, only deep enough to locate the main drill accurately.

5. Tool Used

Center Drilling:
Center drill (also called combined drill and countersink), often 60° or 90° included angle.
Spot Drilling:
Standard twist drill or spot drill (small diameter, rigid).

6. Application

Center Drilling:
Used in lathe operations, turning, and as a pilot for other drilling.
Spot Drilling:
Used before any drilling operation, especially on large, flat, or smooth surfaces.

7. Accuracy Requirement

Center Drilling:
Precise location is important to align with the lathe or turning center.
Spot Drilling:
Extremely precise positioning is required to prevent drill wandering.

8. Material Removal

Center Drilling:
Moderate; removes enough material to fit the center.
Spot Drilling:
Minimal; only removes a small portion to guide the drill.

Summary Table

Feature	Center Drilling	Spot Drilling
Purpose	Align workpiece for turning or drilling	Guide main drill, prevent wandering
Hole Shape	Conical, sometimes with flat tip	Shallow depression, flat or slightly angled
Depth	Moderate to deep	Very shallow
Tool	Center drill	Spot drill / twist drill
Application	Lathe work, pilot for drilling	Precise drilling setup on flat surfaces
Material Removal	Moderate	Minimal