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Turning
Boring Bar Speeds & Feeds (L/D Chart)
Internal turning fights physics. As the bar gets longer (L/D increases), you MUST reduce speed and depth to prevent chatter.
The Golden Rule: Always use the largest diameter bar that fits in the hole, with the shortest overhang possible. Rigidity increases with the 4th power of diameter. A 1.0" bar is 16x more rigid than a 0.5" bar.
Parameter Derating by Overhang
| L/D Ratio | Bar Material | Speed (SFM) Factor | Depth of Cut (Ap) Factor | Typical Application |
|---|---|---|---|---|
| Up to 3xD | Steel | 100% (Normal) | 100% (Normal) | Standard Boring |
| 4xD | Steel | 80 - 90% | 70 - 80% | Limit of Steel Bars |
| 4xD - 5xD | Heavy Metal / Carbide | 90% | 80% | Deep Boring (Standard) |
| 6xD | Solid Carbide | 70 - 80% | 50 - 60% | Requires Carbide Shank |
| 8xD - 10xD | Carbide (Damped) | 50 - 60% | 20 - 30% | Silent Tools / Vibration Damped |
| 10xD + | Specialty Damped | 30 - 50% | 10 - 20% | Extreme Reach (Light finishing only) |
Fighting Chatter?
Tip: Reduce nose radius! A large nose radius pushes the bar away from the cut (radial deflection). Use a 0.015" (0.4mm) or smaller radius for long reach.
Need Base Speeds?
Check our Master Cutting Speed Chart for the implementation starting point (100%), then apply the derating factors above.