Reference data
CNC cutting data by material
The starting surface speeds and chip loads behind the feeds and speeds calculator. Each figure is a conservative published starting point, drawn principally from free tool-maker charts such as Harvey Tool and Lakeshore Carbide. They are starting values, not limits.
| Material | Group | SFM (HSS) | SFM (carbide) | Chip load @ 1/4" (in/tooth) | Hardness (HB) |
|---|---|---|---|---|---|
| Aluminum 2024 | Aluminum | 250 | 750 | 0.0020 | 120 |
| Aluminum 6061 | Aluminum | 250 | 800 | 0.0020 | 95 |
| Aluminum 7075 | Aluminum | 250 | 750 | 0.0019 | 150 |
| Alloy Steel 4140 | Steel | 70 | 300 | 0.0013 | 200 |
| Alloy Steel 4340 | Steel | 60 | 280 | 0.0013 | 220 |
| C45W Carbon Steel (1.1730) | Steel | 80 | 330 | 0.0013 | 170-200 |
| Mild Steel 1018 | Steel | 90 | 350 | 0.0015 | 126 |
| Steel 12L14 (free-machining) | Steel | 110 | 400 | 0.0016 | 160 |
| 1.2767 Tool Steel (45NiCrMo16) | Tool steel | 45 | 250 | 0.0012 | 230-260 |
| D2 Tool Steel | Tool steel | 40 | 200 | 0.0006 | 220-250 |
| O2 Tool Steel | Tool steel | 40 | 200 | 0.0008 | 200-229 |
| Stainless Steel 303 (free-machining) | Stainless | 60 | 250 | 0.0013 | 160 |
| Stainless Steel 304 | Stainless | 50 | 200 | 0.0012 | 170 |
| Titanium Ti-6Al-4V | Titanium | 35 | 150 | 0.0010 | 330 |
| Gray Cast Iron | Cast iron | 70 | 300 | 0.0016 | 200 |
| Brass 360 (free-cutting) | Brass / bronze | 200 | 500 | 0.0020 | 100 |
| Copper C110 (ETP) | Brass / bronze | 150 | 400 | 0.0020 | 50 |
| Acetal (Delrin) | Plastic | 400 | 1,000 | 0.0025 | - |
SFM is the recommended surface speed in surface feet per minute; carbide runs faster than HSS. Chip load is the starting feed per tooth shown for a 1/4 in end mill; smaller tools take less and larger tools take more. Hardness (HB) is the approximate Brinell hardness shown for context.
How to read this
Pick your material, read the surface speed for your tool material into the surface speed calculator to get RPM, then take the chip load into the chip load calculator for a feed rate. The feeds and speeds calculator does both at once. Always start a little under these numbers on a light or flexible setup and climb up once the cut proves stable.
Starting speeds and feeds, material by material
The same figures as the table, worked through to a spindle speed and a feed rate so there is nothing left to look up. Each block assumes a 1/4 in four-flute end mill, because that is the tool most of these numbers get read for; scale the RPM inversely with diameter and the feed with the chip load your own tool calls for. Values marked class-anchored are not grade-specific published figures - they come from the nearest published material class and should be treated as conservative starting points.
What SFM should I use cutting Aluminum 2024?
Start at 750 SFM with carbide (class-anchored), about 11,450 RPM on a 1/4 in end mill. With HSS drop to 250 SFM (class-anchored), about 3,800 RPM. The starting chip load at that diameter is 0.002 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 91.7 in/min.
Hardness about 120 HB. Also sold as 2024-t3, duralumin.
What SFM should I use cutting Aluminum 6061?
Start at 800 SFM with carbide, about 12,200 RPM on a 1/4 in end mill. With HSS drop to 250 SFM (class-anchored), about 3,800 RPM. The starting chip load at that diameter is 0.002 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 97.8 in/min.
Hardness about 95 HB. Also sold as 6061-t6, aircraft aluminum.
What SFM should I use cutting Aluminum 7075?
Start at 750 SFM with carbide, about 11,450 RPM on a 1/4 in end mill. With HSS drop to 250 SFM (class-anchored), about 3,800 RPM. The starting chip load at that diameter is 0.0019 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 87.1 in/min.
Hardness about 150 HB. Also sold as 7075-t6, zinc aluminum.
What SFM should I use cutting Alloy Steel 4140?
Start at 300 SFM with carbide, about 4,600 RPM on a 1/4 in end mill. With HSS drop to 70 SFM (class-anchored), about 1,050 RPM. The starting chip load at that diameter is 0.0013 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 23.8 in/min.
Hardness about 200 HB. Also sold as chromoly, 42crmo4.
What SFM should I use cutting Alloy Steel 4340?
Start at 280 SFM with carbide (class-anchored), about 4,300 RPM on a 1/4 in end mill. With HSS drop to 60 SFM (class-anchored), about 900 RPM. The starting chip load at that diameter is 0.0013 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 22.2 in/min.
Hardness about 220 HB. Also sold as nickel-chromoly.
What SFM should I use cutting C45W Carbon Steel (1.1730)?
Start at 330 SFM with carbide (class-anchored), about 5,050 RPM on a 1/4 in end mill. With HSS drop to 80 SFM (class-anchored), about 1,200 RPM. The starting chip load at that diameter is 0.0013 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 26.2 in/min.
Annealed / as-supplied (about 170-200 HB). Hardness about 170-200 HB. ISO machining group P. Also sold as 1.173, c45, 1045, mould plate.
What SFM should I use cutting Mild Steel 1018?
Start at 350 SFM with carbide, about 5,350 RPM on a 1/4 in end mill. With HSS drop to 90 SFM (class-anchored), about 1,400 RPM. The starting chip load at that diameter is 0.0015 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 32.1 in/min.
Hardness about 126 HB. Also sold as low-carbon steel, mild steel.
What SFM should I use cutting Steel 12L14 (free-machining)?
Start at 400 SFM with carbide (class-anchored), about 6,100 RPM on a 1/4 in end mill. With HSS drop to 110 SFM (class-anchored), about 1,700 RPM. The starting chip load at that diameter is 0.0016 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 39.1 in/min.
Hardness about 160 HB. Also sold as leaded screw stock, free-machining steel.
What SFM should I use cutting 1.2767 Tool Steel (45NiCrMo16)?
Start at 250 SFM with carbide (class-anchored), about 3,800 RPM on a 1/4 in end mill. With HSS drop to 45 SFM (class-anchored), about 700 RPM. The starting chip load at that diameter is 0.0012 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 18.3 in/min.
Soft-annealed (about 230-260 HB) - the state 1.2767 is machined in before hardening. Hardness about 230-260 HB. ISO machining group P. Also sold as x45nicrmo4, 6f7.
What SFM should I use cutting D2 Tool Steel?
Start at 200 SFM with carbide, about 3,050 RPM on a 1/4 in end mill. With HSS drop to 40 SFM (class-anchored), about 600 RPM. The starting chip load at that diameter is 0.0006 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 7.3 in/min.
Soft-annealed (about 220-250 HB) - the state D2 is machined in before hardening. Hardness about 220-250 HB. ISO machining group P. Also sold as 1.2379, x153crmov12, sverker 21, k110, skd11.
What SFM should I use cutting O2 Tool Steel?
Start at 200 SFM with carbide (class-anchored), about 3,050 RPM on a 1/4 in end mill. With HSS drop to 40 SFM (class-anchored), about 600 RPM. The starting chip load at that diameter is 0.0008 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 9.8 in/min.
Soft-annealed (max 229 HB per EN ISO 4957) - the state O2 is machined in before hardening. Hardness about 200-229 HB. ISO machining group P. Also sold as 1.2842, 90mncrv8, 9mn2v, k720.
What SFM should I use cutting Stainless Steel 303 (free-machining)?
Start at 250 SFM with carbide (class-anchored), about 3,800 RPM on a 1/4 in end mill. With HSS drop to 60 SFM (class-anchored), about 900 RPM. The starting chip load at that diameter is 0.0013 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 19.9 in/min.
Hardness about 160 HB. Also sold as free-machining stainless.
What SFM should I use cutting Stainless Steel 304?
Start at 200 SFM with carbide, about 3,050 RPM on a 1/4 in end mill. With HSS drop to 50 SFM (class-anchored), about 750 RPM. The starting chip load at that diameter is 0.0012 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 14.7 in/min.
Hardness about 170 HB. Also sold as 18-8, a2 stainless.
What SFM should I use cutting Titanium Ti-6Al-4V?
Start at 150 SFM with carbide, about 2,300 RPM on a 1/4 in end mill. With HSS drop to 35 SFM (class-anchored), about 550 RPM. The starting chip load at that diameter is 0.001 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 9.2 in/min.
Hardness about 330 HB. Also sold as ti-6-4, grade 5 titanium, tial6v4.
What SFM should I use cutting Gray Cast Iron?
Start at 300 SFM with carbide (class-anchored), about 4,600 RPM on a 1/4 in end mill. With HSS drop to 70 SFM (class-anchored), about 1,050 RPM. The starting chip load at that diameter is 0.0016 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 29.3 in/min.
Hardness about 200 HB. Also sold as gray iron, class 30, g3000.
What SFM should I use cutting Brass 360 (free-cutting)?
Start at 500 SFM with carbide (class-anchored), about 7,650 RPM on a 1/4 in end mill. With HSS drop to 200 SFM (class-anchored), about 3,050 RPM. The starting chip load at that diameter is 0.002 in/tooth, so a four-flute cutter at the carbide speed feeds roughly 61.1 in/min.
Hardness about 100 HB. Also sold as c360, free-machining brass.
What SFM should I use cutting Copper C110 (ETP)?
Start at 400 SFM with carbide (class-anchored), about 6,100 RPM on a 1/4 in end mill. With HSS drop to 150 SFM (class-anchored), about 2,300 RPM. The starting chip load at that diameter is 0.002 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 48.9 in/min.
Hardness about 50 HB. Also sold as electrolytic tough pitch copper, pure copper.
What SFM should I use cutting Acetal (Delrin)?
Start at 1000 SFM with carbide (class-anchored), about 15,300 RPM on a 1/4 in end mill. With HSS drop to 400 SFM (class-anchored), about 6,100 RPM. The starting chip load at that diameter is 0.0025 in/tooth (class-anchored), so a four-flute cutter at the carbide speed feeds roughly 152.8 in/min.
Also sold as pom, polyoxymethylene.
Every figure above is read from the same dataset as the table and carries the same sources. Where a grade has no separately published milling data the value is anchored to its nearest material class and labelled class-anchored; see methodology for how those anchors are chosen and the calculator to run your own tool diameter and flute count.