Boring Bars — Catalog and Selection Guide
Summary
[[Boring]] bars are precision tools designed to enlarge existing holes with exceptional accuracy and surface finish. Available in solid carbide and indexable configurations, boring bars range from micro sizes (0.030" diameter) to heavy-duty applications (1"+ diameter). Selection depends on hole diameter, depth, material, and required tolerance. Solid carbide bars offer superior rigidity for precision work, while indexable bars provide cost-effective tooling for larger diameters and production environments.
Types and Specifications
Solid Carbide Boring Bars
Micro Boring Bars (0.030" - 0.125")
- Harvey 23330 series: 0.030" - 0.125" diameter
- 4-flute helical design for chip evacuation
- Available coatings: Uncoated, AlTiN (C3), TiB2 (C8)
- L/D ratios: 3:1 to 5:1 maximum recommended
- Shank sizes: 1/8" standard
| Part Number | Diameter | Length of Cut | Overall Length | Shank | Coating |
|---|---|---|---|---|---|
| 2331M-C3 | 0.0394" | 0.1562" | 1.5" | 0.125" | AlTiN |
| 23347-C3 | 0.0469" | 0.1875" | 1.5" | 0.125" | AlTiN |
| 23362-C8 | 0.0625" | 0.25" | 1.5" | 0.125" | TiB2 |
| 23378-C3 | 0.0781" | 0.3125" | 1.5" | 0.125" | AlTiN |
| 23393-C6 | 0.0937" | 0.375" | 1.5" | 0.125" | AlTiN |
Standard Boring Bars (0.125" - 0.375")
- Harvey 2340M and 7316 series
- Increased rigidity with larger shanks (3/16", 1/4", 3/8")
- 70% stronger than round neck equivalents
- Square neck design for maximum rigidity
| Part Number | Diameter | Length of Cut | Overall Length | Shank | Coating |
|---|---|---|---|---|---|
| 2343M-C6 | 0.1181" | 0.375" | 1.5" | 0.125" | AlTiN |
| 23409-C3 | 0.1406" | 0.5625" | 2.0" | 0.1875" | AlTiN |
| 731610-C3 | 0.1562" | 0.625" | 2.0" | 0.1875" | AlTiN |
| 2345M-C8 | 0.1968" | 0.75" | 2.5" | 0.25" | TiB2 |
| 2346M-C6 | 0.2362" | 0.875" | 2.5" | 0.25" | AlTiN |
| 23416-C8 | 0.25" | 0.875" | 2.5" | 0.25" | TiB2 |
Coating Selection Guide
Uncoated (Base Models)
- Best for [[aluminum-6061]] and soft materials
- Allows for resharpening
- Lower cost option
- SFM: 200-800 depending on material
AlTiN Coating (C3/C6 suffix)
- General purpose coating for [[4140-steel]] and [[304-stainless]]
- Temperature resistance to 1800°F
- Reduces built-up edge formation
- 2-3x tool life over uncoated
TiB2 Coating (C8 suffix)
- Premium coating for [[titanium-ti6al4v]] and [[inconel-718]]
- Extreme hardness and wear resistance
- Low friction coefficient
- Best for interrupted cuts and high-temp alloys
Speeds and Feeds by Material
Steel Applications
[[4140-steel]] (28-32 HRC)
- SFM: 200-350 (coated), 150-250 (uncoated)
- Feed: 0.001-0.003" per tooth for finishing
- Depth of cut: 0.005-0.020" finishing passes
- Coolant: Flood recommended
[[1018-1045-steel]]
- SFM: 300-500 (coated), 200-350 (uncoated)
- Feed: 0.002-0.005" per tooth
- Can push higher feeds with TiB2 coating
Stainless Steel
[[304-stainless]]
- SFM: 180-280 (avoid work hardening speeds)
- Feed: 0.0015-0.004" per tooth
- Maintain constant feed to prevent [[work-hardening]]
- AlTiN coating essential for tool life
Aluminum
[[aluminum-6061]]
- SFM: 800-1500 (uncoated preferred)
- Feed: 0.003-0.008" per tooth
- Sharp cutting edges critical
- Flood coolant or air blast for chip clearing
Difficult Materials
[[titanium-ti6al4v]]
- SFM: 120-200 (TiB2 coating required)
- Feed: 0.001-0.003" per tooth
- Light depths of cut: 0.005-0.015"
- Constant feed engagement essential
[[inconel-718]]
- SFM: 80-150 (TiB2 coating mandatory)
- Feed: 0.0008-0.002" per tooth
- Ceramic inserts for production work
- Maintain sharp tools - dull tools work-harden material
Selection Criteria
L/D Ratio Guidelines
Micro Applications (under 0.125")
- Maximum L/D: 6:1 for finishing
- Reduce speed 10% for each additional L/D beyond 4:1
- Consider [[chatter-vibration]] dampening techniques
Standard Applications (0.125" - 0.375")
- Maximum L/D: 5:1 for production work
- 3:1 ideal for best surface finish
- Use shortest possible overhang
Hole Diameter vs Bar Size
Clearance Requirements
- Minimum 0.050" clearance for chip evacuation
- 0.020" minimum for finishing operations
- Deeper holes need proportionally more clearance
Rigidity Calculations
- Deflection = (Force × Length³) / (3 × E × I)
- Use largest possible bar diameter
- Square shanks increase rigidity 40% over round
Common Problems and Solutions
Chatter Issues
Symptom: Poor surface finish, dimensional variation Causes: Excessive L/D ratio, wrong speeds, insufficient rigidity Solutions:
- Reduce overhang to minimum
- Decrease SFM by 20-30%
- Use heavier bar diameter
- Add [[chatter-vibration]] damping compound
- Increase feed rate to load tool
Forum Experience: "Had chatter at 0.675" bore but not 0.864" with same 1/2" bar. Smaller diameter gives less support to bar. Dropped to 240 SFM and increased feed to 0.0015"/rev - problem solved."
Poor Surface Finish
Built-up Edge on Aluminum
- Use uncoated tools with sharp edges
- Increase SFM to 1000+ if rigidity allows
- Polish tool cutting edge
- Ensure adequate chip clearing
Work Hardening in Stainless
- Maintain constant feed engagement
- Use positive rake geometry
- Don't dwell at bottom of holes
- AlTiN coating reduces tendency
Tool Breakage
Micro Boring Bars
- Check for proper speeds (often run too fast)
- Ensure gradual engagement
- Use climb boring when possible
- Maximum depth per pass: 2x bar diameter
Shop Floor Tips
Setup and Workholding
Machinist Experience: "Always indicate your bar in the holder - even 0.001" runout shows up in surface finish. Use shortest possible overhang, even if it means multiple setups."
Coolant Strategy:
- Through-coolant bars show 30-50% improvement in tool life
- Air blast minimum for aluminum to prevent chip packing
- Mist systems adequate for steel finishing operations
Programming Considerations
Feed Rate Management:
- Start cuts with 50% programmed feed for first 0.010"
- Maintain constant chip load - don't vary feed rates
- Back-boring (climb) often gives better finish than conventional
Depth Control:
- Program 0.0005" spring passes for critical dimensions
- Allow for tool deflection in tight tolerance work
- Multiple finish passes better than single heavy cut
Tool Life Optimization
Coating Performance:
- TiB2 shows 3-5x life in titanium vs AlTiN
- Uncoated carbide can be resharpened 4-6 times economically
- AlTiN coating fails suddenly - monitor for edge chipping
Maintenance:
- Stone cutting edges between jobs to maintain sharpness
- Check runout after each tool change
- Replace at first sign of edge wear - don't push to failure
Related Topics
- [[boring]] — Basic boring operation fundamentals and techniques
- [[insert-selection-guide]] — Indexable boring bar insert selection
- [[cnmg-inserts]] — Common indexable inserts for larger boring bars
- [[chatter-vibration]] — Diagnosing and solving boring bar chatter issues
- [[tool-wear-diagnosis]] — Identifying when boring bars need replacement
- [[surface-finish-problems]] — Troubleshooting boring surface finish issues
- [[cnc-lathe-setup]] — Setup procedures for boring operations on CNC lathes
- [[turning-basics]] — Fundamental lathe operations including boring