04.6 · Materials & Machinability
Machinability Decision Guide
This page brings it all together: when you pick up a new material, follow this checklist to choose tooling, speeds, feeds, and coolant without guessing.
The Machinability Checklist
For any new material, work through these questions in order:
- What is the hardness? HB or HRC? This sets the speed range.
- Does it work-harden? Stainless, titanium, Inconel = yes. Cast iron, aluminum = no.
- How well does it conduct heat? Aluminum = great. Titanium/Inconel = poor → lower speed.
- Is it abrasive? Cast iron, high-silicon aluminum, composites = yes → wear-resistant tool grade.
- What surface finish is needed? Ra < 1.6 µm = finishing pass with light feed.
- How much stock needs removal? Heavy roughing = prioritize tool life. Finish = prioritize surface finish.
Quick-Start Speed Reference
| Material family | Vc range (carbide) | fz rough (mm/tooth) | Coolant | Tool grade |
|---|---|---|---|---|
| Aluminum (6061, 7075) | 300–600 m/min | 0.03–0.08 | Flood or air blast | K10 polished |
| Brass (free-cutting) | 200–400 m/min | 0.05–0.15 | Optional | K10 |
| Low-carbon steel (1018, 1045) | 180–280 m/min | 0.05–0.15 | Flood | P20–P35 TiN/TiCN |
| Alloy steel (4140 annealed) | 150–250 m/min | 0.05–0.15 | Flood | P20–P35 CVD |
| Pre-hard steel (HRC 28–32) | 100–160 m/min | 0.04–0.10 | Flood | P10–P20 coated |
| Stainless 304/316 | 80–120 m/min | 0.04–0.10 | Heavy flood | M20–M30 TiAlN |
| Cast iron (gray/ductile) | 80–150 m/min | 0.05–0.15 | Dry / air | K20 uncoated |
| Titanium Ti-6Al-4V | 40–80 m/min | 0.04–0.10 | High pressure | K10 polished, variable helix |
| Inconel 718 | 30–60 m/min | 0.03–0.08 | High pressure | S grade / ceramic |
| Hardened steel HRC 50+ | 60–120 m/min (hard mill) | 0.03–0.08 | Minimal | CBN / advanced carbide |
Troubleshooting by Symptom
| Symptom | Likely cause | Fix |
|---|---|---|
| Built-up edge (BUE) on tool | Speed too low, tool not sharp | Increase speed, hone edge, use positive rake |
| Tool wears fast (flank wear) | Speed too high, material abrasive | Reduce Vc 20%, use wear-resistant grade |
| Poor surface finish (lay marks) | Feed too high, nose radius too small | Reduce feed, larger nose radius |
| Chatter / vibration | Overhang too long, tool flex | Reduce stickout, lower ae, sharper edge |
| Long stringy chips | Ductile material, no chip breaker | Use chip-breaker geometry, increase feed |
| Work hardening (surface glaze) | Light feed, rubbing, stainless/Ti | Increase feed, sharper tool, never dwell |
| Burning / discoloration | Speed too high, insufficient coolant | Reduce Vc, increase coolant pressure/flow |
Calculate everything: Material Property Reference · Spindle Speed · Feed Rate · Cutting Speed · MRR