XXIAOMAN TOOLSCutting Tools · Since 2016

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Drill Speed Calculator

Most drill bits do not wear out — they get cooked. Printed speed charts assume a plain HSS bit and a machine that can hit any RPM you like, and say neither out loud. This one asks what bit you are holding and what you are holding it in, then tells you the speed to set and whether your drill can even get there.

Material
= 0.315"
Bit grade

The baseline every printed speed chart silently assumes.

Target speed
1,100RPM
Set your machine to
1,100RPM
Cutting speed
28 m/min
Feed
0.12 mm/rev

Handbook range: 1,000–1,200 RPM (Vc 25–30 m/min). On a drill press that works out to about 134 mm/min of downfeed.

This machine can hold the right speed for that hole.

Coolant: Cutting oil or soluble-oil mix — always

Chips should look like: Long silver spirals coming off both flutes

Blue or straw-coloured chips mean the edge is past its tempering temperature. Stop, cool it, halve the speed and push harder.

The one formula worth knowing

Every drill bit has a cutting speed (Vc) — how fast the outer corner of the cutting edge should travel through the material, in metres per minute. It belongs to the material and the bit, not to your machine. Your drill is marked in RPM, so you convert:

RPM = Vc × 1000 ÷ (π × D) ≈ Vc × 318 ÷ D

Two things fall out of that division, and between them they explain most of what goes wrong:

Full drill speed chart

Every material at the six diameters people actually search for. Switch the bit grade and the whole table recalculates — which is exactly what a printed chart cannot do, because it was set in HSS and never told you.

Recommended drill RPM by material and bit diameter
MaterialVc (m/min)3 mm5 mm6 mm8 mm10 mm13 mm
Mild / low-carbon steel283,0001,8001,5001,100900700
Stainless steel 304 / 316121,250750650480380290
Cast iron222,3001,4001,150900700550
Aluminium707,400max4,500max3,700max2,8002,2001,700
Brass / bronze505,300max3,200max2,7002,0001,6001,200
Copper384,000max2,4002,0001,5001,200950
Hardwood10010,600max6,400max5,300max4,000max3,200max2,400
Plastics / acrylic363,800max2,3001,9001,4501,150900

Greyed figures marked “max” are above what most drill presses can reach — the material is not the limit there, your machine is. “As charted” uses the grade each material is normally drilled with (cobalt for stainless, HSS for the rest) and matches our published speed chart

Coolant and chips, by material

MaterialCoolantChips should look like
Mild / low-carbon steelCutting oil or soluble-oil mix — alwaysLong silver spirals coming off both flutes
Stainless steel 304 / 316Cutting oil, generously — lubrication matters more than coolingShort tight curls, still silver
Cast ironNone — drill dryGrey powder and short flakes, not spirals
AluminiumParaffin, WD-40 or a wax stickLong stringy spirals — clear them before they pack the flutes
Brass / bronzeDry, or a light oilShort broken chips — brass is meant to chip, not curl
CopperLight oilLong soft spirals
HardwoodDryClean shavings, no smoke and no scorch marks
Plastics / acrylicDry, clear the flutes oftenContinuous ribbon

Common questions

What RPM should I drill stainless steel at?+
Far slower than you think. Stainless 304/316 wants a cutting speed of only 10–12 m/min, so a 6 mm cobalt bit runs at about 640 RPM and a 10 mm bit at about 380 RPM. With plain HSS instead of cobalt, drop another 30%. The common mistake is running stainless at mild-steel speed, which glazes the surface — and work-hardened 304 is harder than the bit that hardened it.
What speed for a 10 mm drill bit?+
It depends entirely on the material: roughly 900 RPM in mild steel, 380 RPM in stainless with a cobalt bit, 700 RPM in cast iron, 1,600 RPM in brass and 2,200 RPM in aluminium. Diameter alone never gives you a speed — the outer edge of the bit has a speed limit set by what it is cutting.
What is the drill speed formula?+
RPM = cutting speed × 1000 ÷ (π × diameter in mm), which is usually written RPM = Vc × 318 ÷ D. Cutting speed (Vc) is a property of the material and the bit, measured in metres per minute. For example mild steel at Vc 28 with an 8 mm bit gives (28 × 318) ÷ 8 = about 1,110 RPM.
Does a cobalt bit let me drill faster?+
In stainless and hardened steel, yes — M35 cobalt holds its hardness at temperature, which is worth roughly 40% more speed than plain HSS. In mild steel the gain is mostly tool life rather than RPM, because the limit there is the chip welding to the edge rather than the edge softening.
Why do my drill bits keep burning out?+
Almost always too much speed and too little feed. A bit that rubs instead of cutting generates heat without removing metal. Watch the chips: long silver spirals mean it is right, fine dust means too fast or blunt, blue or straw-coloured chips mean the edge has passed its tempering temperature and is already ruined.
My drill press will not go slow enough — what do I do?+
That is extremely common: a typical 5-step bench press bottoms out at 620 RPM, which is already too fast for anything above 8 mm in steel. Set the calculator to your machine and it will tell you how far over you are. Short-term, flood the hole with cutting oil and ease the feed; properly, a 12-speed pillar drill or a magnetic drill is the fix for large holes in steel.
What feed rate should I use when drilling?+
About 0.015 mm per revolution per millimetre of diameter in steel — so roughly 0.12 mm/rev for an 8 mm bit, which is 130 mm/min at 1,100 RPM. Aluminium and wood take more, stainless slightly less but with firm constant pressure. The rule that matters: if the chips stop while the bit is still turning, you are rubbing, not cutting.

Related guides

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