Surface speed ranges for coated carbide and HSS across the ISO P/M/K/N/S/H material groups — in SFM and m/min, with the formula that turns each figure into a spindle speed for your cutter diameter.
Surface speed (SFM / m min⁻¹) is where every speeds-and-feeds calculation starts. The table below gives the working range for coated carbide on the materials machined most often, grouped by the ISO P/M/K/N/S/H classes used across tooling catalogues. Take the middle of the range as your starting point, then adjust for the operation.
| ISO | Material | SFM (carbide) | m/min (carbide) | SFM (HSS) |
|---|---|---|---|---|
| P | Low carbon steel (<0.25% C) | 400–700 | 120–215 | 80–120 |
| Medium carbon steel (1045) | 350–600 | 105–180 | 70–100 | |
| Alloy steel (4140, 4340) | 250–500 | 75–150 | 50–80 | |
| Tool steel, annealed | 180–350 | 55–105 | 40–60 | |
| M | 304 / 316 stainless | 200–400 | 60–120 | 40–60 |
| 17-4 PH stainless | 150–300 | 45–90 | 30–50 | |
| Duplex / PH stainless | 120–250 | 35–75 | 25–40 | |
| K | Grey cast iron | 400–900 | 120–275 | 70–120 |
| Ductile / nodular iron | 300–600 | 90–180 | 50–90 | |
| Compacted graphite iron | 250–500 | 75–150 | 40–70 | |
| N | Aluminium 6061 / 7075 | 1000–3000 | 300–900 | 200–500 |
| Brass, bronze | 600–1500 | 180–450 | 150–300 | |
| Copper | 500–1200 | 150–365 | 120–250 | |
| Plastics, composites | 500–2000 | 150–600 | 200–600 | |
| S | Titanium Ti-6Al-4V | 150–300 | 45–90 | 25–45 |
| Inconel 718 / 625 | 80–180 | 25–55 | 15–30 | |
| Waspaloy, Rene alloys | 60–150 | 18–45 | 12–25 | |
| Cobalt-based alloys | 60–120 | 18–36 | 12–20 | |
| H | Hardened steel 45–55 HRC | 150–350 | 45–105 | — |
| Hardened steel 55–62 HRC | 80–250 | 25–75 | — | |
| Chilled cast iron, hard facing | 60–180 | 18–55 | — |
Coated carbide, general-purpose grade, moderate depth of cut, rigid setup, flood coolant. HSS figures assume cobalt or premium HSS. Single-point turning usually sits at the top of the range; end milling at the middle; drilling and tapping at the bottom.
Surface speed is independent of cutter size; spindle speed is not. One formula converts the chart value into a number you can dial in:
Worked example: 4140 alloy steel at 300 SFM with a 1/2″ end mill — RPM = (300 × 3.82) ÷ 0.5 = 2,292 RPM. The same 300 SFM on a 1″ cutter is 1,146 RPM, and on a 1/4″ cutter 4,584 RPM. Same surface speed, very different machine settings — which is why the chart has to be converted, not copied.
The SFM to m/min converter handles the unit bridge, SFM / surface speed converts to RPM, and speed & feed takes it through to feed rate and MRR.
The range in the table is wide on purpose — the right point inside it depends on the job, not the material alone. Take the low end when any of these apply, the high end when the setup is strong.
| Push toward the low end | Push toward the high end |
|---|---|
| Interrupted cut, cast skin or hard spots | Continuous cut, clean material |
| Long overhang or thin, flexible workpiece | Short, rigid setup in a solid fixture |
| Deep radial engagement (full slot width) | Light radial engagement, trochoidal or high-feed path |
| Small cutter, high length-to-diameter ratio | Large cutter, short flute length |
| No coolant, or coolant that is not reaching the edge | Through-tool or high-pressure flood coolant |
| Tapping, reaming, or a finish pass | Roughing where the finish does not matter |
| Tool life is the priority (long unattended run) | Cycle time is the priority (one-off job) |
With coated carbide, 4140 sits around 250 to 500 SFM (75 to 150 m/min). A 1/2" end mill at 300 SFM runs at about 2,292 RPM. Take the low end for interrupted cuts or long overhangs, the high end for a rigid setup with good coolant.
Aluminium 6061 and 7075 run from 1,000 to 3,000 SFM (300 to 900 m/min) on carbide, and the limit is usually the machine spindle rather than the cutter. The constraint that matters more than speed is geometry: you need a high-helix, polished flute to stop the material welding to the edge.
Titanium has low thermal conductivity, so heat stays in the cutting edge instead of leaving with the chip. Ti-6Al-4V runs 150 to 300 SFM (45 to 90 m/min) on carbide. Going faster does not clear the heat, it just takes the edge temperature past what the coating can survive.
RPM = (SFM x 3.82) / D, with D in inches. For metric, n = (Vc x 1000) / (pi x D) with Vc in m/min and D in mm. So 300 SFM on a 1/2" cutter is 2,292 RPM, and the same 300 SFM on a 1/4" cutter is 4,584 RPM.
Both, but not at the same point in the range. Single-point turning usually runs at the top of the range because the cut is continuous and the tool is supported. End milling sits in the middle. Drilling and tapping sit at the bottom, because the cutting speed is measured at the outer corner and chip evacuation limits how hard you can push.
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