Reference Chart
Magnesium Feeds & Speeds Chart
Quick-look reference data for magnesium milling, plus the fire-safety and chip-thickness decisions that must be settled before any calculator output goes near the machine.
FIRE HAZARD: Magnesium Ignition Risk
Magnesium chips and fines ignite at 473°C (883°F). Fine dust can create flash fires. You MUST have proper safety protocols before machining magnesium.
- Class D fire extinguisher within arm's reach. NEVER use water, CO2, or foam — they intensify magnesium fires.
- No water-based coolant on fine chips — hydrogen gas generation risk. Use mineral oil or specialized Mg coolant.
- Chip management: Collect in covered steel containers. Never mix with steel chips (galvanic corrosion generates hydrogen).
- Avoid fine cuts: Very light finishing passes create thin, hot chips that ignite easily. Maintain substantial chip thickness.
Need RPM & Feed After Safety Checks?
Use a calculator only after this chart and your shop procedures confirm the job is set up for safe magnesium cutting. Chip thickness, fire control, and coolant choice matter as much as the raw SFM number.
Reference handoff
Magnesium table handoff
Use this chart for magnesium ranges only after safety controls are understood, then branch into calculator release checks.
Best starting point
Magnesium milling reference ranges for first-pass comparison.
Branch when
Fire control, drilling, and chip-thickness checks need process-specific validation.
Magnesium Release Math
Formula Chain
Formula chain: magnesium release = SFM/RPM/feed math + minimum chip thickness + chip evacuation + Class D fire-control readiness.
Worked Example
Worked example: AZ31B roughing at 1,200 SFM with a 0.5 in end mill converts to about 9,170 RPM; at 0.006 in/tooth and three flutes, feed is about 165 IPM before fire-control, chip collection, and coolant checks.
Release Boundary
Release boundary: do not run magnesium from calculator output until Class D extinguishing, dry chip collection, coolant policy, fine-chip controls, and shop approval are in place.
Wrought Magnesium (AZ31B / AZ61A)
Sheet and plate alloys used in aerospace structures and automotive panels. AZ31B is the most common wrought grade. Excellent machinability — among the lowest cutting forces of any structural metal.
| Operation | SFM (Carbide) | Chip Load (1/2" EM) | DOC (Roughing) |
|---|---|---|---|
| Roughing | 800 - 1500 | 0.005" - 0.010" | 1.0D - 2.0D |
| Finishing | 1200 - 2000 | 0.002" - 0.004" | 0.02" - 0.05" |
| Drilling | 300 - 600 | 0.005" - 0.012"/rev | — |
Roughing and finishing rows are the primary workflow here. The drilling row is reference-only on this chart; validate peck depth, hole evacuation, and fire controls in the drilling calculator.
Cast Magnesium (AZ91D / AM60B / ZK60A)
Die-cast and sand-cast alloys for automotive housings (transmission cases, steering columns). AZ91D is the dominant die-cast grade. Harder and more abrasive than wrought due to silicon content in some variants.
| Alloy | Operation | SFM (Carbide) | Chip Load (1/2" EM) |
|---|---|---|---|
| AZ91D | Roughing | 600 - 1200 | 0.004" - 0.008" |
| AZ91D | Finishing | 1000 - 1800 | 0.002" - 0.003" |
| ZK60A (High Strength) | Roughing | 500 - 1000 | 0.003" - 0.006" |
Frequently Asked Questions
What SFM should I use for magnesium?
Wrought AZ31B: 800–1500 SFM roughing, 1200–2000 SFM finishing. Cast AZ91D: 600–1200 SFM roughing. Magnesium allows among the highest cutting speeds of any structural metal.
Can I use water-based coolant on magnesium?
Treat coolant as a safety decision first, not a generic feeds-and-speeds setting. Some magnesium operations run successfully with approved water-based systems, but fine chips and fines can generate hydrogen if the process control is poor. Many shops stay with mineral oil, specialized magnesium-safe coolant, or dry evacuation. Do not copy a coolant choice into drilling or fine-finishing work without validating the fire procedure.
What fire extinguisher do I need for magnesium?
Class D only (dry powder agents like Met-L-X or Lith-X). NEVER use water, CO2, foam, or Halon — these react violently with burning magnesium, intensifying the fire and potentially causing explosions.
What coating should I use for machining magnesium?
Uncoated polished carbide is standard. Magnesium is so soft and generates so little heat that coatings provide minimal benefit. ZrN is acceptable if you also machine aluminum with the same tools.