Boring-Everything you need to know

Boring is a lathe machining operation used to enlarge, finish, or improve the accuracy of an existing hole in a workpiece. A single-point cutting tool, known as a boring bar, is fed axially into the rotating workpiece.

This process ensures better dimensional accuracy, surface finish, and concentricity of internal cylindrical surfaces.

Boring Operation in Lathe Machining

1. What is Boring?

Boring is a lathe machining operation used to enlarge, true, and finish an existing hole in a workpiece using a single-point cutting tool called a boring tool or boring bar.
Unlike drilling, boring improves accuracy, alignment, and surface finish of the hole.

2. Purpose of Boring

To increase the diameter of a pre-drilled or cast hole
To correct inaccuracies (out-of-roundness, taper, misalignment)
To achieve close tolerances
To obtain a smooth internal surface
To prepare holes for fitting bearings, bushings, or shafts

3. Principle of Boring

The workpiece rotates in the spindle.
The boring tool is fed longitudinally (parallel to the axis).
Material is removed from the internal surface of the hole.

4. Difference Between Drilling and Boring

Drilling	Boring
Produces a new hole	Enlarges an existing hole
Less accurate	Highly accurate
Multi-point tool	Single-point tool
Poor finish	Good finish

5. Types of Boring

a) External Boring

Tool acts on the inside surface
Most common lathe boring operation

b) Internal Boring

Enlargement of internal cylindrical holes

c) Taper Boring

Produces a conical hole
Done using compound rest or taper attachment

d) Step Boring

Produces holes of different diameters

e) Fine / Finish Boring

Final pass for accuracy and surface finish

6. Boring Tools

Single-Point Boring Tool
- HSS or carbide
- Used on manual lathes
Boring Bar
- Long shank for deep holes
- May have indexable inserts
Adjustable Boring Tool
- Used for precision sizing

Tool geometry:

Proper clearance angle
Small nose radius
Sharp cutting edge

7. Boring Operation Setup

Work holding: 3-jaw chuck, 4-jaw chuck, faceplate
Tool setting:
- Tool tip at center height
- Minimum tool overhang (to avoid chatter)
Hole requirement: Hole must be pre-drilled or cast

8. Steps in Boring Operation (Manual Lathe)

Drill or ensure an existing hole.
Mount workpiece securely in chuck.
Fix boring bar in tool post.
Set tool exactly at center height.
Start lathe at suitable speed.
Feed tool longitudinally inside the hole.
Take multiple light cuts.
Measure diameter frequently.
Perform finishing pass.

9. Cutting Parameters (Typical)

Cutting speed: Lower than turning
Feed: 0.05–0.3 mm/rev
Depth of cut: Small, gradual cuts
Coolant: Improves finish and reduces heat

10. Common Problems & Remedies

Problem	Cause	Remedy
Chatter	Long tool overhang	Reduce overhang
Tapered hole	Tool deflection	Use rigid setup
Rough finish	Blunt tool	Sharpen tool
Oversize hole	Excess depth	Reduce cut, measure often