4140 Steel Speeds and Feeds (Milling, Drilling, Turning)
Carbide end mills in 4140 Steel: 200–400 SFM. Also called AISI 4140, chromoly, 41L40. Chart row used: “Steels – Med Carbon” (Annealed alloy steel (medium-carbon row)).
Starting point: carbide end mills
RPM and IPM use the low end of the published range (200 SFM and the lowest chip load for each diameter range). RPM = SFM × 12 ÷ (π × D); IPM = RPM × flutes × chip load.
| Diameter | Chip load (in/tooth) | RPM | IPM · 2 flute | IPM · 3 flute |
|---|---|---|---|---|
| 1/8" | .0005 | 6,112 | 6.1 | 9.2 |
| 1/4" | .0006 | 3,056 | 3.7 | 5.5 |
| 3/8" | .0010 | 2,037 | 4.1 | 6.1 |
| 1/2" | .0015 | 1,528 | 4.6 | 6.9 |
| 3/4" | .0020 | 1,019 | 4.1 | 6.1 |
| 1" | .0025 | 764 | 3.8 | 5.7 |
| Diameter | Chip load (in/tooth) | RPM | IPM · 2 flute | IPM · 3 flute |
|---|---|---|---|---|
| 3 mm | .0005 | 6,468 | 6.5 | 9.7 |
| 6 mm | .0006 | 3,234 | 3.9 | 5.8 |
| 10 mm | .0015 | 1,940 | 5.8 | 8.7 |
| 12 mm | .0015 | 1,617 | 4.9 | 7.3 |
| 16 mm | .0020 | 1,213 | 4.9 | 7.3 |
| 20 mm | .0025 | 970 | 4.9 | 7.3 |
Full published chip-load ranges
- 1/32-1/8": .0005–.0010"
- 1/8-1/4": .0006–.0018"
- 1/4-3/8": .0010–.0025"
- 3/8-1/2": .0015–.0035"
- 1/2-3/4": .0020–.0040"
- 3/4-1": .0025–.0050"
Calculator — prefilled for 4140 Steel
Material library
Tool & coating guidance
Grade, edge geometry and coating determine usable cutting data. Sharp polished edges can suit nonferrous work; substrate and geometry still govern. No coating speed multiplier is inferred.
Tool & cut parameters
Target parameters
Spindle RPM
1,528
Feed Rate (IPM)
9.2
Max chip hex
0.0014"
Chip thinning & cutter body
Fixed-angle peripheral estimate: hex = fz × radial factor × sin(KAPR). No radial correction at ≥50% engagement. Not a centered face-milling or ball-nose model. Sandvik geometry reference
Insert styles, guidelines & formulas
RPM = (SFM × 12) / (π × D) | Feed = RPM × programmed fz × effective zc
Milling Guidelines
- Start at 70% of max SFM, increase gradually
- Chip load too low → rubbing & heat buildup
- Use climb milling when machine rigidity allows
- Radial engagement >50% → reduce feed per tooth
- Round inserts: best for ramp-in and 3D surfaces
Drilling and turning
The source chart covers carbide end mills only, so we don't list drilling or turning numbers for 4140 Steel. Enter your drill or insert maker's cutting data in the drilling calculator or turning calculator.
Machinist tips
- Chip thinning
- At light radial engagement (under half the cutter diameter) the real chip is thinner than the feed per tooth. Raise the feed to keep the chip at the chart value, or the tool rubs and wears.
- Climb vs conventional
- On a rigid CNC, climb mill so each tooth starts thick and exits thin. Use conventional milling on machines with backlash or on hard scale skins.
- Coolant
- Flood coolant or mist controls heat. Coated carbide (such as AlTiN) handles steel heat better than uncoated.
Common questions
- What SFM should I use for 4140 Steel?
- Lakeshore Carbide – General Purpose End Mill Speeds & Feeds lists 200–400 SFM for carbide end mills in the "Steels – Med Carbon" row. Start at the low end and adjust for your machine.
- What chip load for a 1/2" end mill in 4140 Steel?
- The published range for 3/8–1/2" carbide end mills is .0015–.0035" per tooth. At 200 SFM a 3-flute 1/2" end mill runs about 1528 RPM and 6.9 IPM.
- Are these values for HSS tools, drilling or turning?
- No. The source chart covers carbide end mills only. Use your drill or insert maker's data for drilling and turning.
Sources
- Lakeshore Carbide – General Purpose End Mill Speeds & Feeds — “Steels – Med Carbon” row (SFM and chip load per tooth).
- Lakeshore Carbide speeds and feeds charts
Starting values only. Adjust for rigidity, tool manufacturer data and machine.
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