Spindle speed is RPM = SFM x 3.82 / diameter (in) and feed is IPM = RPM x flutes x chip load, so a 1/2 in HSS drill in mild steel at 70 to 80 SFM turns about 535 to 610 RPM.
Speeds and feeds calculator
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Starting surface speeds by material are in the table below.
Speeds and feeds: starting surface speeds (SFM) for HSS and carbide by material
Starting surface speed by material (drilling)
Material
HSS, low (SFM)
HSS, high (SFM)
Carbide, low (SFM)
Carbide, high (SFM)
HSS, low (m/min)
HSS, high (m/min)
Carbide, low (m/min)
Carbide, high (m/min)
HSS source line
Carbide source line
Aluminum alloys
200
300
300
600
61
91
91
183
Besly: Aluminum and Aluminum Alloys
Amana: Aluminum/Aluminum Alloys
Brass (free-cutting and common brass)
200
300
200
300
61
91
61
91
Besly: Brass and Bronze, Common
Amana: Brass
Low-carbon (mild) steel
70
80
150
300
21
24
46
91
Besly: Low Carbon Steel
Amana: Low Carbon Steels
Alloy steel, below 260 HB (annealed)
35
75
100
200
11
23
30
61
Besly: Alloy Steel below 260 Brinell
Amana: Medium Carbon Steels
Alloy steel, 260 to 321 HB (pre-hardened)
15
25
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5
8
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Besly: Alloy Steel 260 - 321 Brinell
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Stainless steel, free-machining
30
60
100
150
9
18
30
46
Besly: Stainless Steel
Amana: Free Machining Stainless Steels
Stainless steel, work-hardening (austenitic)
30
60
50
100
9
18
15
30
Besly: Stainless Steel
Amana: Work Hardening Stainless Steels
Cast iron, soft (gray)
100
150
200
300
30
46
61
91
Besly: Soft Cast Iron
Amana: Soft Cast Irons
Cast iron, medium hard
70
100
125
225
21
30
38
69
Besly: Medium Hard Cast Iron
Amana: Medium Cast Irons
Plastics (thermoplastics)
100
150
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30
46
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Besly: Thermoplastics
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Starting points only. These are drilling speeds from the two makers' charts. Besly says most jobs need adjustment from its speeds, which depend on material, hole depth, cutting fluid, the machine, the hole quality wanted and the setup; Amana calls its values recommendations only; Nachi says to adjust when unusual vibration or a different sound occurs. Where your tool maker publishes a chart for that tool, use it.
RPM = SFM x 3.82 / D (Amana; Besly rounds the constant to 3.8), with D the tool (or, on a lathe, the work) diameter in inches; 3.82 is 12 / pi. Metric: RPM = 1000 x Vc / (pi x D), Vc in m/min and D in mm (Sandvik Coromant). 1 SFM = 0.3048 m/min (1 ft = 0.3048 m exactly, NIST SP 811).
Feed rate (in/min) = RPM x number of flutes x chip load per tooth (in) (University of Pennsylvania guide). For drills, Amana gives inches per revolution = chip load x number of flutes.
Besly suggested feeds for HSS drills (in/rev): under 1/8 in dia .001-.002; 1/8 to 1/4 in .002-.004; 1/4 to 1/2 in .004-.007; 1/2 to 1 in .007-.015; 1 in and over .015-.025.
The carbide row for annealed alloy steel uses Amana's "Medium Carbon Steels" line, since Amana has no line named for alloy steel. Amana has no line matching 260-321 HB alloy steel or plastics, so those carbide cells are empty. Besly gives one stainless line (30-60 SFM) for both stainless rows.
m/min columns are SFM x 0.3048, rounded.
Cross-checked against Nachi America, HSS/HSCO Drill Series Catalog, p. 22 "Standard Drilling Condition" (uncoated jobber drills, List No. 500) and University of Pennsylvania, MEAM Design Lab, Feeds and Speeds guide (HSS and carbide end mills) and Redline Tools (Productivity Inc.), General Purpose Carbide Endmills Speeds & Feeds (p. 216) and High Speed Steel and Cobalt Endmills Speeds & Feeds (p. 220): HSS ranges overlap Besly for alloy steel (40-52), stainless (30-40) and medium cast iron (55-72 SFM). Nachi is more conservative for mild steel (50-65 vs 70-80), soft cast iron (55-72 vs 100-150) and aluminum and nonferrous metals (83-115 vs 200-300 SFM). The table keeps Besly's values and labels them starting points.; End-mill starting speeds: HSS aluminum 300, brass 150, mild steel 100, stainless 80, plastics 400 SFM; carbide aluminum 600+, brass 300, mild steel 250, stainless 200, plastics 600+ SFM. Carbide figures fall inside or just above the Amana ranges (stainless is higher for milling); HSS figures sit at or above the top of the Besly drilling ranges, as expected for milling against drilling.; Uncoated carbide end mills: low-carbon steel 200-250, medium-carbon 200-250, austenitic stainless 200-250, gray cast iron 250-350, brass 250-350, aluminum over 500 SFM, all at or above the Amana drilling ranges. Its HSS/cobalt end-mill figures (e.g. aluminum 600-800, mild steel 150-200 SFM) are well above the drilling values, which confirms the drill-based numbers here are the conservative end..
The two formulas
Speed. RPM = SFM x 3.82 / D, where SFM is the cutting speed in surface feet per minute and D is the tool diameter in inches (on a lathe, the work diameter). The 3.82 is 12 / pi, which turns feet into inches of circumference. Amana Tool prints this formula on its carbide drill chart, and Besly Cutting Tools prints it with the constant rounded to 3.8.
Feed. IPM = RPM x number of flutes x chip load, where chip load is the thickness each cutting edge takes per revolution, in inches per tooth. The University of Pennsylvania guide gives the same formula for milling, and Amana gives a drill's feed per revolution as chip load x number of flutes.
Metric. RPM = 1000 x Vc / (pi x D), with Vc in m/min and D in mm, as Sandvik Coromant gives it. Feed in mm/min = RPM x flutes x chip load in mm. One foot is exactly 0.3048 m, so 1 SFM is 0.3048 m/min.
Worked examples
HSS drill, mild steel. Besly suggests 70 to 80 SFM for low-carbon steel. For a 1/2 in drill: 70 x 3.82 / 0.5 = 535 RPM up to 80 x 3.82 / 0.5 = 611 RPM. At Besly's 0.007 in/rev for a 1/2 in drill, 535 RPM gives 535 x 0.007 = 3.7 in/min.
Carbide drill, aluminum. Amana gives 300 to 600 SFM for aluminum alloys. A 1/4 in drill at 300 SFM runs 300 x 3.82 / 0.25 = 4,584 RPM; at Amana's 0.007 in/rev feed that is 32 in/min.
Carbide end mill, aluminum. The University of Pennsylvania's machine shop guide starts carbide end mills in aluminum at 600 SFM with 0.004 in per tooth for a 1/2 in cutter. A 1/2 in, 3-flute end mill: 600 x 3.82 / 0.5 = 4,584 RPM, and 4,584 x 3 x 0.004 = 55 in/min.
Where the starting speeds come from
The table pairs Besly's suggested speeds for high speed steel drills with Amana Tool's recommendations for solid carbide drills, by material. In these charts carbide runs about two to three times the HSS speed in steel, free-machining stainless and cast iron (mild steel: 70 to 80 SFM HSS, 150 to 300 carbide), less than double in aluminum (200 to 300 against 300 to 600) and work-hardening stainless, and the same in brass (200 to 300 for both).
Published charts do not agree closely. Nachi's chart for uncoated HSS jobber drills is more conservative, for example 83 to 115 SFM for aluminum and 50 to 65 SFM for carbon steel. End mill charts run faster again: the University of Pennsylvania guide starts HSS end mills in aluminum at 300 SFM and carbide at 600 SFM. Treat every number here as a place to start, and when the maker of the tool in your hand publishes a chart, use theirs.
Adjusting from the starting point
Besly calls its speeds the approximate range for efficient operation under normal conditions and says most jobs need some adjustment to reach peak efficiency. Within the range, higher speed means fewer holes before the drill needs regrinding and lower speed more holes, so the best speed trades output against tool cost.
Besly lists the variables that move the right speed: material composition and hardness, hole depth, cutting fluid, the type and condition of the machine, the hole quality wanted and the difficulty of the setup.
Nachi's chart assumes coolant in a vertical machine. It says to use pecking in a horizontal machine or a deep hole, and to adjust the drilling condition when unusual vibration or a different sound occurs.
Amana says to replace or resharpen drills at the first sign of dulling or rounding.
Besly's feed ranges for HSS drills are 0.001 to 0.002 in/rev under 1/8 in diameter, 0.002 to 0.004 for 1/8 to 1/4 in, 0.004 to 0.007 for 1/4 to 1/2 in, and 0.007 to 0.015 for 1/2 to 1 in.
Materials in the table
The rows cover aluminum, brass, mild steel, annealed and pre-hardened alloy steel, free-machining and austenitic stainless, soft and medium cast iron, and thermoplastics. Besly gives a single 30 to 60 SFM line for stainless; Amana splits carbide speeds into 100 to 150 SFM for free-machining stainless and 50 to 100 SFM for work-hardening stainless. Outokumpu, the stainless producer, names 303 as a free-machining grade (0.15 to 0.35% sulfur added) and says austenitic stainless steels have the greatest tendency to work harden. Amana has no line that matches pre-hardened alloy steel at 260 to 321 HB or plastics, so those carbide cells are blank rather than guessed. Drill sizes and decimal equivalents are on the drill bit size chart.