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Magnesium Speeds and Feeds
Guide · Updated October 28, 2026
Magnesium alloys are among the easiest metals to machine: low cutting force, great finish and very high speeds. The one thing to manage is fine chips and dust, which can ignite. Thick chips, sharp tools and a tidy chip routine keep it routine shop work.
Check sizes after the cut
Magnesium expands more than steel (about 14 millionths per inch per °F). Check with a mic proved on gage blocks once the part is at room temperature. The free Gage Block Calculator builds the stack.
Step by step
- Identify the alloy: AZ31 sheet and plate, AZ91 castings and ZK60 forgings all machine similarly.
- Use sharp tools: Sharp, high-rake carbide or HSS with polished flutes; dull tools rub and make fine chips and heat.
- Pick a starting SFM: Carbide roughly 1,000–3,000+ SFM; HSS around 600–1,000 SFM, limited by machine and rigidity.
- Take a real chip: Chip loads similar to or heavier than aluminum, e.g. 0.002–0.006 in per tooth; thick chips are much harder to ignite than fines.
- Choose coolant: Dry or mineral-oil cutting fluid is common. Avoid water-based coolant unless it is formulated for magnesium, because wet magnesium chips can release hydrogen.
- Manage chips: Clear chips often, store them in a covered, labeled steel container, and do not mix with other metal swarf or grinding dust.
- Have the right extinguisher: Keep a Class D extinguisher or dry sand nearby; never use water on a magnesium fire.
Worked example
Milling AZ31 plate with a 1/2 in 3-flute carbide end mill at 1,500 SFM: RPM = 3.82 × 1,500 ÷ 0.500 = 11,460 RPM. If the spindle tops out at 8,000 RPM, the effective SFM = 8,000 × 0.500 ÷ 3.82 = 1,047 SFM, which is still fine. At 0.004 in per tooth, feed = 8,000 × 3 × 0.004 = 96 IPM. That heavy chip load keeps chips thick and the edge cool.
Chip and dust safety in plain terms
Solid magnesium bar is hard to ignite. The risk is fine chips, dust and grinding swarf from rubbing or dull tools. Keep tools sharp, avoid long dwells, do not grind or sand magnesium on equipment used for steel, and clean up chips each shift.
Common problems
Sparks or glowing chips usually come from a dull or rubbing tool; stop the cut and change it. Built-up edge on castings means too low a rake. Size change means the part was still warm.
Tips
- Compare: aluminum speeds and feeds.
- Fluids: cutting fluid basics.
- Tools: carbide end mill basics.
FAQ
Is magnesium dangerous to machine?
It is routine with sharp tools, thick chips, tidy chip handling and a Class D extinguisher on hand.
What SFM for magnesium?
Roughly 1,000–3,000 SFM with carbide, often limited by spindle speed.
Can I use water-based coolant?
Only coolant made for magnesium; otherwise use dry cutting or mineral oil.
How do I put out a magnesium fire?
Class D extinguisher or dry sand; never water.
How should I store chips?
In a covered, labeled steel container, kept apart from other swarf.
Related guides and calculators
- Aluminum Speeds and Feeds
- Milling Speeds and Feeds
- Cutting Fluid and Coolant Basics
- Carbide End Mill Basics
- Turning Speeds and Feeds
- All free machinist calculators
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