Cutting oil (low-viscosity with EP additives) is the traditional first choice for deep hole drilling. Emulsions work when cooling dominates. Synthetics are generally not preferred due to poor lubrication. The right choice depends on method, material, and environmental requirements.
| Property | Cutting Oil | Emulsion | Synthetic |
|---|---|---|---|
| Lubrication | Excellent (+++) | Moderate (++) | Poor (+) |
| Cooling | Poor (−) | Good (++) | Excellent (+++) |
| Chip Flushing | Good (++) | Good (++) | Excellent (+++) |
| Corrosion Protection | Excellent (+++) | Good (++) | Moderate (+) |
| Bio-stability | Excellent | Poor (daily maint.) | Good |
| Fire Risk | Moderate | Low | Low |
| Lifecycle Cost | Lower (longer life) | Higher (maintenance + disposal) | Moderate |
| Condition | Recommended | Conc. |
|---|---|---|
| Hard-to-machine (SS, Ti, Ni alloys) | Cutting oil, high EP | Neat |
| High-speed ferrous drilling | Emulsion or semi-synthetic | 8–10% |
| Aluminum / non-ferrous | Emulsion or synthetic | 10% |
| Cast iron | Emulsion + cleaning | 7% |
| Max precision / surface finish | Cutting oil | Neat |
| High L/D (>50:1) | Low-viscosity cutting oil | Neat |
| Environmentally sensitive | Synthetic or vegetable oil | Neat/mixed |
| High-pressure (>70 bar) | Cutting oil with EP | Neat |
| Titanium / superalloys | Cutting oil, high sulfur EP | Neat |
| Additive | Activates | Best For |
|---|---|---|
| Sulfur (active, S 8–17%) | ~400–800°C | SS, Ti, superalloys |
| Sulfur (inactive, S <5%) | ~500–900°C | Steel, general (less staining) |
| Chlorinated paraffin | ~200–400°C | High load, low speed; restricted in some regions |
| Phosphorus-based | ~200–500°C | Non-ferrous, aluminum |
| ZDDP | ~300–600°C | Steel, cast iron |
| Bore Dia. | ISO VG | Application |
|---|---|---|
| <5mm | VG 5–10 | Micro holes, small gundrills |
| 5–20mm | VG 10–15 | General gundrilling |
| 20–50mm | VG 15–22 | BTA / ejector |
| >50mm | VG 22–32 | Large bore BTA |
| Method | Ra Reduction | Tool Life | Energy |
|---|---|---|---|
| Flood (baseline) | Baseline | Baseline | Baseline |
| LN&sub2; Cryogenic | 44–70% better | Significantly improved | Moderate |
| MQL | Comparable | 50–100% longer | 64% of flood |
| CO&sub2; + MQL Hybrid | 65% better | Best combination | 64% of flood |
| Method | Target filtration |
|---|---|
| Gundrilling | ≤20 μm (mandatory for coolant orifices) |
| BTA / STS | ≤30 μm |
| Ejector (DTS) | ≤30 μm (protect Venturi ring) |
| Skive & burnish | ≤10 μm |