Complete Machinability Ratings
Baseline: AISI 1212 free-machining steel = 100%. Higher = easier to machine.
Carbon Steels
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| 12L14 | Leaded | 170% | Easiest steel to machine |
| 1215 | — | 136% | High sulfur free-machining |
| 1117 | — | 100% | |
| 1018 | Cold drawn | 78% | General purpose mild steel |
| 1020 | Annealed | 72% | Low carbon, gummy |
| 1045 | As-rolled | 57% | Most common shaft steel, moderate |
| 1095 | Annealed | 42% | High carbon, abrasive |
Alloy Steels
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| 4140 | Annealed | 66% | Standard for drill collars |
| 4140 | Q&T (300 HB) | 45% | Reduced speeds required |
| 4340 | Annealed | 57% | High-strength alloy |
| 4340 | Q&T (350 HB) | 38% | Difficult |
| 8620 | Annealed | 66% | Carburizing grade |
| 300M | Annealed | 40% | Aerospace, very difficult |
Stainless Steels
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| 303 | Free-machining | 78% | Best stainless for machining |
| 416 | Free-machining | 85–110% | High sulfur, good chip break |
| 304 | Annealed | 45% | Work-hardens severely |
| 316 | Annealed | 36–45% | Tougher than 304 |
| 17-4 PH | H900 | 38% | Precipitation-hardened |
| Duplex 2205 | Annealed | 30% | Very difficult |
Aluminum and Non-Ferrous
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| 6061-T6 | T6 | 200–270% | Most common structural Al |
| 7075-T6 | T6 | 140–240% | High-strength Al |
| 2024-T4 | T4 | 180% | Aircraft aluminum |
| C360 brass | Free-cutting | 300% | Easiest common metal |
| Copper (C110) | Annealed | 70% | Gummy chips |
Titanium and Superalloys
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| Ti-6Al-4V | Annealed | 22% | Poor thermal conductivity |
| Ti-6Al-4V | Aged | 18% | Even harder |
| Inconel 718 | Aged | 12–15% | Extremely difficult |
| Inconel 625 | Annealed | 15% | Similar to 718 |
| Hastelloy X | Annealed | 12% | Very difficult |
| Waspaloy | Aged | 10% | Most difficult common alloy |
Tool Steels
| Grade | Condition | Rating | Notes |
|---|---|---|---|
| P20 | Pre-hardened (30 HRC) | 55–65% | Best tool steel for machining |
| H13 | Annealed | 50–60% | Pre-machine before HT |
| H13 | Hardened (52 HRC) | 20–25% | Slow speeds only |
| A2 | Annealed | 55–65% | Moderate |
| D2 | Annealed | 40% | High carbide abrasion |
| D2 | Hardened (60 HRC) | 15% | Extremely difficult |
Drilling Speed Adjustment Factor
Multiply the base cutting speed by the machinability factor:
| Rating | Speed Factor vs 1045 (57%) |
|---|---|
| 200% (Al 6061) | × 3.5 |
| 100% (1117) | × 1.75 |
| 57% (1045 baseline) | × 1.0 |
| 45% (304 SS) | × 0.8 |
| 22% (Ti-6Al-4V) | × 0.4 |
| 12% (Inconel 718) | × 0.2 |
Cost Impact of Low Machinability
| Rating | Relative Tool Cost | Relative Cycle Time |
|---|---|---|
| 200%+ (Aluminum) | 0.3× | 0.3× |
| 57% (1045 baseline) | 1.0× | 1.0× |
| 45% (304 SS) | 1.5× | 1.3× |
| 22% (Titanium) | 3.0× | 2.5× |
| 12% (Inconel) | 4–5× | 4–5× |
Source: ISCAR Die & Molds Guide; PMPA Craftsman; MSCI machinability ratings; Ficient Design; SawbladeUniversity.