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Milling 1018 and 4140 steel: end mill speeds and feeds
Published carbide end mill SFM and chip load for 1018 mild steel and 4140 alloy steel, side by side from Harvey Tool, Kyocera SGS and 6GTools, with slotting limits and worked examples.
1018 and 4140 are the two steels most shops cut every week, and the published numbers for them spread wider than most people expect. Harvey Tool's general table gives 100-300 SFM for carbide in 10XX steels [1]. 6GTools lists 350 SFM for 1018 with uncoated carbide, 420 with TiN and 500 with AlTiN, and 250 / 300 / 350 SFM for 4140 [2]. Kyocera SGS's general-purpose end mill catalog puts 1018-class carbon steel at 460 SFM for profiling and 335 SFM for slotting, and 4140-class alloy steel at 335 and 245 SFM [3].
ChiploadPro's calculator starts carbide in 1018 at 350 SFM. That is above Harvey's general range, equal to 6GTools's uncoated figure, and inside SGS's slotting range. The calculator doesn't cover 4140 yet, so use the table below for it.
Surface speed, carbide end mills
| Source | 1018 (low-carbon) | 4140 (alloy) | Conditions |
|---|---|---|---|
| Harvey Tool general guidelines [1] | 100-300 | no 41XX row | 10XX / 11XX / 13XX row |
| 6GTools, uncoated / TiN / AlTiN [2] | 350 / 420 / 500 | 250 / 300 / 350 | "Mild" steel group |
| Kyocera SGS, profiling [3] | 460 (368-552) | 335 (268-402) | 1018 ≤ 175 Bhn; 4140 ≤ 275 Bhn / ≤ 28 HRc |
| Kyocera SGS, slotting [3] | 335 (268-402) | 245 (196-294) | same |
| ChiploadPro calculator | 350 | - | carbide, any coating |
Chip load by diameter
| Dia. | Harvey 10XX [1] | 6GTools mild [2] | SGS carbon [3] | SGS alloy [3] | Digital Machine [4] | ChiploadPro 1018 |
|---|---|---|---|---|---|---|
| 1/8" | .0005 | .0006 | .0003 | .0002 | .0005-.001 | .0005 |
| 1/4" | .0015 | .0017 | .0008 | .0006 | .0015-.0025 | .0013 |
| 3/8" | .002 | .0025 | .0015 | .0011 | .002-.0035 | .0019 (interpolated) |
| 1/2" | .003 | .0028 | .0020 | .0015 | .0025-.004 | .0025 |
| 3/4" | .005 | .0033 | .0024 | .0018 | .0035-.0055 | .0035 |
| 1" | .006 | .0041 | .0028 | .0021 | .004-.007 | .0047 (extrapolated) |
Inches per tooth. 6GTools gives one chip-load row for its mild-steel group, which covers both 1018 and 4140 [2]. Digital Machine's "mild & low-alloy steel" range covers 1018, 1045 and 4140/4340 up to about 32 HRC, compiled from Machinery's Handbook and maker charts [4].
Slotting vs. profiling
SGS runs slots about 25-30% slower than profiling passes and limits slot depth by flute count: 1 × D deep with 2 flutes, 0.5 × D with 3, and 0.4 × D with 4. For profiling it allows up to 1.5 × D axial, with radial width up to 0.5 × D for 2 flutes and 0.25 × D for 3-4 flutes [3]. Harvey recommends 4 flutes for slotting ferrous material, 3-5 for traditional roughing, 5-14 for finishing and 5-7 for high-efficiency milling [5]. See choosing flute count.
Light radial cuts need more feed
Below 50% radial engagement the chip gets thinner than the programmed feed per tooth. 6GTools multiplies chip load by 1.1 at 30% width, 1.2 at 20%, 1.4 at 15%, 1.8 at 10% and 2.3 at 5% [2]. Harvey's formula gives a similar curve, 1.67× at 10% [6]. The chip thinning guide walks through the math.
Worked example: 1/2" 4-flute slot in 1018
ChiploadPro start: 350 × 3.82 ÷ 0.5 = 2,674 RPM. At .0025 in/tooth: 2,674 × 4 × .0025 = 26.7 IPM. SGS's own slotting line for the same tool is 2,559 RPM and 20.5 IPM [3], so the calculator is about 30% more aggressive on feed than the catalog, but still well under Harvey's .003 in/tooth chip load [1]. At SGS's 0.4 × D limit (0.2" deep), power is 0.5 × 0.2 × 26.7 × 1.00 ÷ 0.80 ≈ 3.3 HP at the motor, using 1.00 hp per in³/min for mild steel [7]. On a small mill, run the slot in two passes.
Worked example: 1/2" 4-flute profile in 4140
SGS: 335 SFM gives 335 × 3.82 ÷ 0.5 = 2,559 RPM. At .0015 in/tooth: 2,559 × 4 × .0015 = 15.4 IPM, the same as SGS's printed feed [3]. At 0.125" wide (0.25 × D) and 0.5" deep, power is 0.125 × 0.5 × 15.4 × 1.40 ÷ 0.80 ≈ 1.7 HP, using 1.40 hp per in³/min for 4140 [7]. 4140 takes about 40% more power than 1018 for the same cut [7].
SGS's alloy row stops at 275 Bhn / 28 HRc [3]. For harder pre-hard stock, start lower and check your tool maker's data.
Open the end mill calculator 304 stainless guide
Related guides
Tooling for this job
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Sources
- [1] Harvey Tool, General Machining Guidelines
- [2] 6GTools, Carbide end mill speeds & feeds
- [3] Kyocera SGS, 2023 Global Catalog: General Application End Mills, speed & feed pp. 320-321 (PDF)
- [4] Digital Machine, Chip Load Chart (compiled from Machinery's Handbook 31st ed. and maker charts)
- [5] Harvey Performance, 5 Questions to Ask Before Selecting an End Mill
- [6] Harvey Performance, How to Combat Chip Thinning
- [7] 4calculators, Milling Spindle Power Calculator (unit power table)