What SFM should I use for Gray Cast Iron · Class 40?

Lakeshore Carbide – General Purpose End Mill Speeds & Feeds lists 100–300 SFM for carbide end mills in the "Cast Irons – Medium" row. Start at the low end and adjust for your machine.

What chip load for a 1/2" end mill in Gray Cast Iron · Class 40?

The published range for 3/8–1/2" carbide end mills is .0015–.0030" per tooth. At 100 SFM a 3-flute 1/2" end mill runs about 764 RPM and 3.4 IPM.

Are these values for HSS tools, drilling or turning?

The end mill chart covers carbide end mills. The "Speeds by tool material" table adds published HSS, turning-insert and drilling rows for Gray Cast Iron · Class 40 where a source lists them (LittleMachineShop, Sandvik Coromant).

Gray Cast Iron · Class 40 Speeds and Feeds (Milling, Drilling, Turning)

Carbide end mills in Gray Cast Iron · Class 40: 100–300 SFM. Also called ASTM A48 Class 40, GG30. Chart row used: “Cast Irons – Medium” (As cast).

Starting point: carbide end mills

RPM and IPM use the low end of the published range (100 SFM and the lowest chip load for each diameter range). RPM = SFM × 12 ÷ (π × D); IPM = RPM × flutes × chip load.

Gray Cast Iron · Class 40 — inch end mills
Diameter	Chip load (in/tooth)	RPM	IPM · 2 flute	IPM · 3 flute
1/8"	.0004	3,056	2.4	3.7
1/4"	.0005	1,528	1.5	2.3
3/8"	.0010	1,019	2.0	3.1
1/2"	.0015	764	2.3	3.4
3/4"	.0020	509	2.0	3.1
1"	.0030	382	2.3	3.4

Gray Cast Iron · Class 40 — metric end mills (inch chip-load range the size falls in)
Diameter	Chip load (in/tooth)	RPM	IPM · 2 flute	IPM · 3 flute
3 mm	.0004	3,234	2.6	3.9
6 mm	.0005	1,617	1.6	2.4
10 mm	.0015	970	2.9	4.4
12 mm	.0015	809	2.4	3.6
16 mm	.0020	606	2.4	3.6
20 mm	.0030	485	2.9	4.4

Full published chip-load ranges

1/32-1/8": .0004–.0005"
1/8-1/4": .0005–.0010"
1/4-3/8": .0010–.0020"
3/8-1/2": .0015–.0030"
1/2-3/4": .0020–.0050"
3/4-1": .0030–.0075"

Calculator — prefilled for Gray Cast Iron · Class 40

Results for Milling

Spindle RPM: 764
Feed: 4.6 IPM
Chip load: 0.0014 in

MRR: 0.17 in³/min
Power: — HP
Torque: — lbf·ft
Programmed fz: 0.0015 in
Actual SFM: 100
Spindle use: 6%

Pick a material in the library below to estimate spindle power and torque.

Operation Type

Milling

Turning

Material library

Auto-adjust cutting data

Material & condition

Cutting tool material

Tool coating

Tool & coating guidance

Grade, edge geometry and coating determine usable cutting data. Sharp polished edges can suit nonferrous work; substrate and geometry still govern. Coated vs uncoated carbide changes turning data only; no coating speed multiplier is inferred.

Tool & cut parameters

Manual values

SFM (Surface Feet/Min)

Cutter Diameter (in)

Number of Flutes

Axial depth of cut (in)

Feed per Tooth (in)

Machine RPM limit

Chip thinning & cutter body

Cutter body

Chip-thinning compensation

Radial engagement (% of diameter)

Entering angle KAPR (°)

Radial factor ×1.09Angle factor ×1.00Programmed fz 0.0015 inMax chip hex 0.0014 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

Insert styles, guidelines & formulas

RPM = (SFM × 12) / (π × D) | Feed = RPM × programmed fz × effective zc | MRR = WOC × DOC × feed | HP = Kp × C × MRR × 1.1 ÷ 0.8 (Machinery's Handbook)

Milling Insert Styles

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

Speeds by tool material

Published starting ranges for Gray Cast Iron · Class 40 by operation and tool material. Rows marked * are estimates.

Gray Cast Iron · Class 40 — speeds by tool material
Operation	Tool	SFM	Feed	Source row
milling	HSS *	70–100	0.0015–0.0030 in/tooth	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
milling	Cobalt HSS (M35/M42) *	70–100	0.0015–0.0030 in/tooth	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
milling	Solid carbide end mill	100–300	0.0015–0.0030 in/tooth	Lakeshore Carbide · Cast Irons – Medium
milling	Uncoated carbide (H13A)	215–340	0.0040–0.0160 in hex	Sandvik milling (large engagement) · CMC 08.2 Gray cast iron, high tensile strength
milling	Coated carbide (GC3220)	510–760	0.0040–0.0120 in hex	Sandvik milling (large engagement) · CMC 08.2 Gray cast iron, high tensile strength
milling	Ceramic (CC6190)	2600–3900	0.0040–0.0120 in hex	Sandvik milling (large engagement) · CMC 08.2 Gray cast iron, high tensile strength
milling	CBN (CB50)	2000–2750	0.0040–0.0080 in hex	Sandvik milling (large engagement) · CMC 08.2 Gray cast iron, high tensile strength
turning	HSS	145–215	0.0040 in/rev	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
turning	Cobalt HSS (M35/M42) *	145–215	0.0040 in/rev	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
turning	Uncoated carbide (H13A)	310–460	0.0040–0.0160 in/rev	Sandvik turning · CMC 08.2 Gray cast iron, high tensile strength
turning	Coated carbide (GC3210)	800–1150	0.0080–0.0240 in/rev	Sandvik turning · CMC 08.2 Gray cast iron, high tensile strength
turning	Ceramic (CC6190)	1650–2600	0.0080–0.0240 in/rev	Sandvik turning · CMC 08.2 Gray cast iron, high tensile strength
turning	CBN (CB7525)	3450–4800	0.0040–0.0160 in/rev	Sandvik turning · CMC 08.2 Gray cast iron, high tensile strength
drilling	HSS	80–100	—	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
drilling	Cobalt HSS (M35/M42) *	80–100	—	LittleMachineShop · Cast iron (ASTM class 20, 25, 30, 35, 40)
drilling	Coated carbide (3234/4234)	295–560	0.0071–0.0165 in/rev	Sandvik CoroDrill 870 · CMC 08.2 Gray cast iron, high tensile strength

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 · Class 40?: Lakeshore Carbide – General Purpose End Mill Speeds & Feeds lists 100–300 SFM for carbide end mills in the "Cast Irons – Medium" row. Start at the low end and adjust for your machine.
What chip load for a 1/2" end mill in Gray Cast Iron · Class 40?: The published range for 3/8–1/2" carbide end mills is .0015–.0030" per tooth. At 100 SFM a 3-flute 1/2" end mill runs about 764 RPM and 3.4 IPM.
Are these values for HSS tools, drilling or turning?: The end mill chart covers carbide end mills. The "Speeds by tool material" table adds published HSS, turning-insert and drilling rows for Gray Cast Iron · Class 40 where a source lists them (LittleMachineShop, Sandvik Coromant).

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