Boring
Enlarging and finishing holes
Process Steps
1. Pre-Operation Check
Verify the existing hole size and required final dimension. Select appropriate boring bar size.
2. Tool Setup
Mount boring bar ensuring minimum overhang for stability. Check tool height is centered with the workpiece.
3. Initial Boring
Start with light cuts to establish roundness and concentricity. Check measurements frequently.
4. Precision Boring
Make progressively lighter cuts as you approach final dimension. Monitor surface finish quality.
5. Final Sizing
Use very light cuts for final passes to achieve required tolerance and surface finish.
Material-Specific Guidelines
Mild Steel
- • Good chip evacuation essential for deep bores
- • Moderate cutting speeds prevent chatter
- • Through-tool coolant beneficial for deep holes
Recommended Speeds: 70-80 SFPM for HSS tools, 200-300 SFPM for carbide
Tooling Notes: Use boring bars with minimum 4:1 length-to-diameter ratio
Cast Iron
- • Excellent boring characteristics
- • Dry cutting possible
- • Chip evacuation critical due to fragmented chips
Recommended Speeds: 50-60 SFPM for HSS tools, 150-200 SFPM for carbide
Tooling Notes: Negative rake inserts work well, high rigidity required
Aluminum
- • Higher cutting speeds possible
- • Built-up edge common at low speeds
- • Good surface finish achievable
Recommended Speeds: 150-200 SFPM for HSS tools, 400-800 SFPM for carbide
Tooling Notes: Polished inserts reduce built-up edge formation
Quality Control Specifications
Bore Diameter
Method: Inside micrometer or bore gauge
Tolerance: ±0.001" typical
Frequency: Every bore, multiple depths
Bore Roundness
Method: Bore gauge readings at multiple angles
Tolerance: 0.0005" TIR typical
Frequency: First piece and periodic checks
Surface Finish
Method: Visual and bore gauge feel
Tolerance: 32-63 microinch typical
Frequency: Every bore
Straightness
Method: Long bore gauge or CMM
Tolerance: 0.002" per foot typical
Frequency: Sample basis for long bores
Operation Difficulty
Intermediate
Safety Guidelines
- • Ensure boring bar is properly secured and not extending too far
- • Check clearances before starting the machine
- • Use appropriate speeds to prevent tool chatter
- • Keep the boring bar perpendicular to the workpiece axis
- • Monitor chip formation and clear chips regularly
Required Tooling
Boring Bars
Various sizes of boring bars for different hole diameters. Minimum bore diameter is typically limited by the boring bar size.
Dial Bore Gauge
For precise measurement of internal diameters during boring operations
Inside Micrometers
For checking precise internal dimensions
Boring Bar Holders
Specialized tool holders for secure mounting of boring bars
Troubleshooting Guide
Chatter in Deep Holes
Reduce boring bar overhang, use dampened bars, adjust speed/feed rates
Taper in Bore
Check boring bar alignment, reduce overhang, verify machine alignment
Poor Surface Finish
Check insert grade and geometry, verify speeds and feeds, ensure rigid setup
Size Control Issues
Use precision boring heads, account for tool deflection, make spring passes
Roundness Problems
Check chuck jaw condition, verify workpiece mounting, ensure proper tool geometry
Pro Tips & Tricks
Boring Bar Selection
Choose largest possible bar diameter for rigidity. Consider anti-vibration bars for deep bores.
Best for: All boring operations, critical for deep holes
Insert Positioning
Orient insert for optimal chip evacuation. Lead angle affects surface finish and chatter.
Best for: Precision boring and finish requirements
Chatter Prevention
Start with maximum bar diameter, minimum overhang. Adjust speed until chatter stops, then reduce 10%.
Best for: Deep boring operations and finish boring
Measurement Technique
Allow bore to cool before measuring. Take readings at multiple depths and angles.
Best for: Precision boring operations