Threading
Cutting internal and external threads
Process Steps
1. Thread Calculation
Determine required thread pitch, major and minor diameters. Calculate depth of cut.
2. Workpiece Preparation
Turn workpiece to major diameter and cut thread relief. Chamfer end for thread start.
3. Tool Setup
Set threading tool exactly at center height and perpendicular to workpiece. Check clearances.
4. Initial Threading
Begin with light cuts, using threading dial for engagement. Check thread form regularly.
5. Progressive Cuts
Make multiple passes, increasing depth gradually. Use compound rest at 29.5° for better chip control.
Material-Specific Guidelines
Mild Steel
- • Good thread quality achievable with proper setup
- • Chip control critical for thread accuracy
- • Cutting fluid important for finish
Recommended Speeds: 30-40 SFPM for HSS tools, 80-120 SFPM for carbide
Tooling Notes: Ground HSS tools work well, carbide for production runs
Stainless Steel
- • Work hardening can affect thread quality
- • Lower speeds required
- • Heavy-duty cutting fluid essential
Recommended Speeds: 20-30 SFPM for HSS tools, 60-90 SFPM for carbide
Tooling Notes: Sharp tools essential, positive rake angles recommended
Brass/Bronze
- • Excellent threading characteristics
- • Minimal cutting fluid needed
- • Higher speeds possible
Recommended Speeds: 40-60 SFPM for HSS tools, 100-150 SFPM for carbide
Tooling Notes: Zero rake tools work well, watch for chip control
Quality Control Specifications
Major Diameter
Method: Thread micrometer or wires
Tolerance: 6g/6h typical class fit
Frequency: Every thread
Thread Pitch
Method: Thread pitch gauge and optical comparator
Tolerance: ±0.001" pitch typical
Frequency: First piece and periodic
Thread Form
Method: Thread profile gauge and visual
Tolerance: Class 2A/2B typical
Frequency: Setup and periodic checks
Thread Runout
Method: Dial indicator on major diameter
Tolerance: 0.002" TIR typical
Frequency: Sample basis
Operation Difficulty
Intermediate
Safety Guidelines
- • Always use threading dial when cutting imperial threads
- • Start with slower speeds for threading operations
- • Ensure proper thread relief is cut before threading
- • Practice thread dial timing on scrap material first
- • Double-check threading tool geometry before starting
Required Tooling
Threading Tool
60-degree included angle for standard threads, properly ground for the specific thread form
Thread Pitch Gauge
For checking thread pitch and form during cutting
Thread Micrometers
Specialized micrometers for measuring thread dimensions
Thread Wires
For precise measurement of thread pitch diameter
Troubleshooting Guide
Incorrect Thread Pitch
Verify gear setup, check threading dial engagement, confirm lead screw condition
Poor Thread Form
Check tool geometry, ensure proper compound angle, verify tool center height
Torn Threads
Reduce cutting speed, check tool sharpness, use proper cutting fluid
Thread Runout
Verify workpiece mounting, check tailstock alignment, use thread relief
Inconsistent Depth
Use thread depth gauge, maintain consistent compound feed, check for backlash
Pro Tips & Tricks
Compound Angle
Set compound rest at 29.5° for most threads. This reduces cutting forces and improves finish.
Best for: All threading operations, especially for tough materials
Threading Dial Use
For imperial threads, engage on any line for even threads, numbered lines for odd threads.
Best for: Manual lathe imperial threading
Depth Calculation
Use 0.866 × pitch for depth of V threads. Add 0.001-0.002" clearance for external threads.
Best for: All standard 60° thread forms
Tool Alignment
Use center gauge or thread tool gauge to set tool exactly perpendicular to workpiece.
Best for: All threading operations, critical for accuracy