Gray Cast Iron Speeds and Feeds (Milling, Drilling, Turning)

    Carbide end mills in Gray Cast Iron: 150–350 SFM. Also called Class 30, Class 40, grey iron. Chart row used: “Cast Irons – Soft” (Gray iron (soft cast iron row)).

    Starting point: carbide end mills

    RPM and IPM use the low end of the published range (150 SFM and the lowest chip load for each diameter range). RPM = SFM × 12 ÷ (π × D); IPM = RPM × flutes × chip load.

    Gray Cast Iron — inch end mills
    DiameterChip load (in/tooth)RPMIPM · 2 fluteIPM · 3 flute
    1/8".00054,5844.66.9
    1/4".00062,2922.84.1
    3/8".00121,5283.75.5
    1/2".00201,1464.66.9
    3/4".00307644.66.9
    1".00405734.66.9
    Gray Cast Iron — metric end mills (inch chip-load range the size falls in)
    DiameterChip load (in/tooth)RPMIPM · 2 fluteIPM · 3 flute
    3 mm.00054,8514.97.3
    6 mm.00062,4262.94.4
    10 mm.00201,4555.88.7
    12 mm.00201,2134.97.3
    16 mm.00309105.58.2
    20 mm.00407285.88.7
    Full published chip-load ranges
    • 1/32-1/8": .0005–.0009"
    • 1/8-1/4": .0006–.0020"
    • 1/4-3/8": .0012–.0028"
    • 3/8-1/2": .0020–.0040"
    • 1/2-3/4": .0030–.0060"
    • 3/4-1": .0040–.0080"

    Calculator — prefilled for Gray Cast Iron

    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

    Manual values

    Target parameters

    Spindle RPM

    1,146

    Feed Rate (IPM)

    9.2

    Max chip hex

    0.0018"

    Chip thinning & cutter body
    %
    Radial factor ×1.09Angle factor ×1.00Programmed fz 0.0020 inMax chip hex 0.0018 in

    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

    Spindle utilization10%
    Insert styles, guidelines & formulas

    RPM = (SFM × 12) / (π × D) | Feed = RPM × programmed fz × effective zc

    Square (SEMT/SNMG)
    General purpose, 90° lead angle
    Round (RPMW/RCKT)
    Ramping, 3D contouring, high feed
    Triangular (TPMX)
    Light cuts, finishing
    Octagonal (ONMU)
    Face milling; HFM suitability is body-specific

    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
    Open in the full calculator workspace

    Drilling and turning

    The source chart covers carbide end mills only, so we don't list drilling or turning numbers for Gray Cast Iron. 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.
    Dry or air blast
    Cast iron is usually cut dry with an air blast to clear abrasive dust. Expect abrasive wear on the edge.

    Common questions

    What SFM should I use for Gray Cast Iron?
    Lakeshore Carbide – General Purpose End Mill Speeds & Feeds lists 150–350 SFM for carbide end mills in the "Cast Irons – Soft" row. Start at the low end and adjust for your machine.
    What chip load for a 1/2" end mill in Gray Cast Iron?
    The published range for 3/8–1/2" carbide end mills is .0020–.0040" per tooth. At 150 SFM a 3-flute 1/2" end mill runs about 1146 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.
    Ductile Iron speeds and feeds1018 Steel speeds and feedsMIC-6 Cast Aluminum speeds and feeds

    Sources

    Starting values only. Adjust for rigidity, tool manufacturer data and machine.

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