What is Machinability?
Machinability is how easy (or difficult) a metal is to cut with standard machining operations — turning, milling, drilling. It’s expressed as a percentage relative to AISI 1212 steel, which is the baseline at 100%.
Higher percentage = easier to machine = lower cost. If you’re selecting a material and you have a choice, machinability can significantly impact your part cost.
Machinability Ratings for Common Metals
| Material | Machinability Rating (%) | Notes |
|---|---|---|
| AISI 1212 (free-machining steel) | 100 | Baseline — the standard |
| AISI 1215 | 136 | Best free-machining carbon steel |
| AISI 12L14 (leaded) | 170 | Easiest steel to machine; lead content helps chip breaking |
| AISI 1018 | 78 | Most common mild steel |
| AISI 1045 | 57 | Medium carbon, widely used |
| AISI 4140 | 66 | Popular alloy steel |
| AISI 4340 | 57 | High-strength alloy steel |
| 303 Stainless Steel | 78 | Free-machining stainless |
| 304 Stainless Steel | 45 | Work hardens easily — use sharp tools |
| 316 Stainless Steel | 36 | Tougher than 304, more expensive to machine |
| 17-4 PH Stainless | 48 | Precipitation hardened, moderate |
| 6061-T6 Aluminum | 270 | Machines beautifully — the go-to for prototypes |
| 7075-T6 Aluminum | 240 | Slightly harder, still excellent |
| Brass (C360) | 300 | Easiest common metal to machine |
| Titanium (Ti-6Al-4V) | 22 | Difficult — slow speeds, high tool wear |
| Inconel 718 | 12 | Extremely difficult — specialized tooling required |
What Affects Machinability?
- Hardness — harder metals wear tools faster (see Hardness & Tensile Strength Guide)
- Work hardening — austenitic stainless steels (304, 316) get harder as you cut them
- Chip formation — free-machining steels (12L14, 1215) have additives that help chips break cleanly
- Thermal conductivity — poor conductors (titanium, Inconel) concentrate heat at the cutting edge
- Abrasiveness — some materials eat through carbide inserts
Practical Advice
- Prototyping? Use 6061 aluminum or 12L14 steel. Fast, cheap, forgiving.
- Need stainless? Start with 303 before jumping to 304 or 316. It’s much cheaper to machine.
- High volume? The machinability rating directly impacts your cycle time and tool costs. A 10% improvement in machinability can translate to significant savings at scale.
Related: AISI/SAE Steel Numbering System | International Steel Grade Equivalents
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