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Drill Speed Chart
Quick answer: Bigger bit, slower speed. A 1/4″ bit in steel wants ~600 RPM; a 1″ bit wants ~150. The governing quantity is surface speed: RPM = (SFM × 12) ÷ (π × diameter).
Recommended RPM for every common bit size across four materials, the formula behind the numbers, and how to read the chips to tell whether you have it right.
Drill speed chart (RPM)
The governing quantity is surface speed — how fast the cutting edge travels through the material, not how fast the chuck turns. A large bit covers far more distance per revolution than a small one, so as diameter goes up, RPM must come down.
| Bit diameter | Softwood | Hardwood | Aluminium | Steel |
|---|---|---|---|---|
| 1/16 | 6000 | 6000 | 3000 | 1500 |
| 1/8 | 6000 | 5000 | 2500 | 1000 |
| 3/16 | 4500 | 3500 | 1750 | 800 |
| 1/4 | 3000 | 2500 | 1200 | 600 |
| 5/16 | 2500 | 2000 | 1000 | 500 |
| 3/8 | 2000 | 1750 | 900 | 400 |
| 1/2 | 1500 | 1250 | 650 | 300 |
| 5/8 | 1250 | 1000 | 500 | 250 |
| 3/4 | 1000 | 750 | 400 | 200 |
| 1 | 750 | 500 | 300 | 150 |
Figures are for high-speed steel twist bits. Carbide-tipped and cobalt bits tolerate higher speeds; masonry bits with hammer action run slower still. Stainless should be run at roughly half the steel column.
Reading the chips
The swarf tells you more than any chart. In metal, you want continuous curls coming off the flutes. Fine powder means you are going too fast and rubbing rather than cutting — which work-hardens the material and destroys the edge. Blue or straw-coloured chips mean the bit is overheating and losing its temper.
| What you see | What it means | Fix |
|---|---|---|
| Long continuous curls | Correct speed and feed | Keep going |
| Fine powder or dust | Too fast, not enough feed | Slow down, push harder |
| Blue or straw chips | Overheating | Slow down, add cutting fluid |
| Squealing | Rubbing, not cutting | More pressure or a sharper bit |
| Burnt wood, smoke | Too slow a feed, or dull bit | Clear the flutes, sharpen or replace |
Material-specific notes
- Stainless steel work-hardens the instant you let the bit rub. Slow speed, firm continuous pressure, cutting fluid, and never let it stop turning while in contact.
- Aluminium is soft and gummy — it welds to the flutes. Fast speed, and a squirt of WD-40 or kerosene as a lubricant stops the build-up.
- Acrylic and polycarbonate crack if the bit grabs on breakthrough. Slow speed, low pressure, and back off as you exit.
- Tile and glass need a diamond or spear-point bit, very slow speed, water cooling, and no hammer action.
- Masonry uses hammer action with a carbide bit at moderate speed — the impact does the work, not the rotation.
Large-diameter bits
Hole saws, spade bits and Forstner bits all cut at a much larger radius than their shank suggests, so they need dramatically lower speeds — a 2″ hole saw in hardwood wants roughly 300 RPM, and a 4″ one closer to 150. Run them at twist-bit speeds and they burn the workpiece and the tool in about the same time.
Frequently asked questions
What RPM should I drill steel at?
For a 1/4 in HSS bit in mild steel, about 600 RPM. Larger bits need less: roughly 300 RPM at 1/2 in and 150 at 1 in. Stainless should run at about half those figures with cutting fluid.
Why do larger drill bits need slower speeds?
Because what matters is surface speed at the cutting edge, not chuck speed. A 1 in bit's edge travels four times as far per revolution as a 1/4 in bit's, so at the same RPM it is cutting four times faster and will overheat.
What speed for drilling aluminium?
Fast — around 1,200 RPM for a 1/4 in bit. Aluminium's problem is not heat but gumming: it welds to the flutes. A lubricant such as WD-40 or kerosene and frequent flute clearing matter more than the exact speed.
How do I know if I am drilling too fast?
Look at the chips. Continuous curls mean you are cutting correctly. Fine powder means the bit is rubbing rather than cutting — slow down and increase pressure. Blue or straw-coloured chips mean it is overheating and losing its hardness.