utting metal requires balance — too slow and you rub, too fast and you melt tools.
Let’s look at how to tune parameters intelligently instead of guessing.
Understand Surface Feet per Minute (SFM)
SFM determines how fast the tool edge travels across the material.
Formula:
RPM = (SFM × 3.82) / Tool Diameter
Typical SFM values:
| Material | SFM | Example RPM (½" tool) |
|---|---|---|
| Aluminum 6061 | 600 | ~4 600 RPM |
| Mild Steel | 300 | ~2 300 RPM |
| Stainless 304 | 180 | ~1 375 RPM |
| Brass | 800 | ~6 100 RPM |
Chip Load per Tooth
Chip Load = Feed / (RPM × Flutes)
For a ¼" 3-flute endmill at 18 000 RPM, 200 IPM feed gives a 0.0037" chip load — ideal for aluminum.
Coolant and Air Blast
Use mist or flood coolant for steels; use air blast for aluminum to evacuate chips.
Re-cutting chips generates heat and micro-welds that destroy edges.
Depth of Cut
Keep radial engagement below 50% when roughing to avoid chatter.
Axial depth can be 1.5–2× tool diameter if rigidity allows — adaptive toolpaths distribute load efficiently.
Tool Material
-
Aluminum: uncoated carbide, polished flutes.
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Steel: TiAlN-coated carbide.
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Brass: uncoated or ZrN.
Lesson
Heat is your biggest enemy. Control it with proper chip thickness, adequate coolant, and balanced engagement.
A cool chip is a happy chip.
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