Parting (Cut-Off)-Everything you need to know

Parting, also known as cut-off, is a lathe operation used to separate a finished part from the remaining workpiece. A thin, narrow cutting tool is fed radially into the rotating workpiece until the material is completely cut through.

This operation is commonly used at the final stage of machining and requires precise tool alignment to ensure a clean and accurate separation.

Parting (Cut-Off) Operation in Lathe Machining

1. What is Parting (Cut-Off)?

Parting, also called cut-off, is a lathe machining operation used to separate a finished component from the parent bar or workpiece.
The cutting tool is fed radially inward until the workpiece is completely cut through.

2. Purpose of Parting

To cut a workpiece to required length
To separate finished parts
To remove excess material
To prepare blanks for further machining

3. Principle of Parting

The workpiece rotates in the spindle.
A narrow parting tool is fed perpendicular to the axis of rotation.
Material is removed progressively until separation occurs.

4. Parting Tools

Single-Point Parting Tool
- Very narrow cutting edge
- HSS or carbide
Blade-Type Parting Tool
- Replaceable blade
- Better rigidity
Indexable Insert Parting Tool
- Used in CNC lathes
- High precision and tool life

Tool geometry:

Tool width as small as possible
Proper clearance angles
Sharp cutting edge
Slight front rake

5. Parting Operation Setup

Work holding: 3-jaw chuck (short overhang preferred)
Tool setting:
- Tool tip at exact center height
- Tool must be perfectly perpendicular to work axis
Tool overhang: Minimum possible
Coolant: Strongly recommended

6. Steps in Parting Operation (Manual Lathe)

Secure the workpiece firmly in the chuck.
Set the parting tool at center height.
Position the tool at required cut-off location.
Start the lathe at suitable speed (lower than turning).
Feed the tool slowly and steadily inward.
Apply coolant continuously.
Reduce feed near the center.
Complete the cut and stop the machine.

7. Cutting Parameters (Typical)

Cutting speed: 30–50% of turning speed
Feed: 0.03–0.08 mm/rev
Depth of cut: Full radius (gradual feed)
Coolant: Essential to prevent tool seizure

8. Common Problems & Remedies

Problem	Cause	Remedy
Tool breakage	Excess feed, misalignment	Reduce feed, align tool
Chatter	Poor rigidity	Reduce overhang, tighten setup
Tool jamming	Chip clogging	Use coolant, peck cutting
Rough cut surface	Blunt tool	Sharpen or replace tool