A drill is a rotating cutting tool that holds a bit in a chuck and removes material to form a round hole. It works by converting motor or hand-crank torque into rotational motion at the bit tip, where two cutting lips shear chips out of the workpiece while flutes evacuate them. The purpose is to make accurate, repeatable holes in wood, metal, masonry, plastic and composites — from a 0.5 mm clock pivot to a 100 mm core hole in concrete. A modern 18 V cordless drill delivers around 60 N·m of torque and 2,000 RPM, enough to drive a 13 mm twist bit through mild steel.
Drill RPM Interactive Calculator
Vary drill bit diameter and cutting surface speed to see the required spindle RPM and rotating bit motion.
Equation Used
The drill RPM equation converts recommended cutting surface speed Vc into spindle speed for a drill diameter D. Larger bits need lower RPM for the same cutting edge speed; smaller bits need higher RPM.
- Metric units: cutting speed in m/min and drill diameter in mm.
- Twist drill cutting edge speed is evaluated at the outside diameter.
- Cordless drill comparison assumes a 2000 RPM high-speed setting from the article.
How the Drill (general) Actually Works
Every drill, regardless of whether it's a hand brace, a benchtop drill press, or an 18 V cordless, does the same three things: clamp the bit, spin it at a controlled RPM, and feed it into the work. The chuck — usually a 3-jaw keyless or keyed type — grips the bit shank concentrically. Runout matters here. A good cordless drill chuck holds runout under 0.1 mm at the tip; a worn or cheap chuck will run out 0.3 mm or more, which means a 6 mm bit cuts a 6.3 mm sloppy hole and breaks small bits at the flute root.
At the bit tip, two cutting lips meet at the point angle — 118° is the standard for general-purpose twist drill bits, 135° for harder steels and stainless. The lips shear chips, and the helical flutes lift those chips up and out of the hole. If the flutes pack with chips because the feed rate is too aggressive or you forgot to peck, the bit overheats, the cutting edge work-hardens the material, and the bit either burns blue or snaps. This is why peck drilling — pulling the bit out every 1-2 bit diameters of depth — exists. It clears the chip and lets coolant or air reach the cutting edge.
Surface cutting speed governs everything. Run a HSS twist drill bit too fast in steel and the cutting edge softens above 600 °C; run it too slow and the bit rubs instead of cutting, which polishes the surface and dulls the edge. The sweet spot for HSS in mild steel is about 30 m/min surface speed. For aluminium it's 90 m/min. For hardwoods, 60 m/min. Convert that to RPM with the bit diameter and you have your spindle setting.
Key Components
- Chuck: Clamps the bit shank concentric to the spindle axis. Quality 3-jaw keyless chucks hold runout under 0.1 mm TIR; loose or worn chucks let the bit wobble and oversize the hole. Typical capacity ranges are 10 mm for compact cordless, 13 mm for full-size cordless and drill presses, 16 mm and up for industrial machines.
- Twist drill bit: The cutting tool itself. HSS for general use, cobalt (M35, M42) for stainless and tough alloys, carbide for hardened steel and abrasive composites. Standard point angle is 118°, with a 135° split point for self-centring on metal. Flute helix is typically 30° for general work, 15° for brass to stop the bit from grabbing.
- Motor and gearbox: Provides torque and RPM. An 18 V brushless cordless drill puts out roughly 60 N·m peak torque through a 2-speed planetary gearbox — low gear 0-500 RPM for driving screws and large bits, high gear 0-2,000 RPM for small bits in wood. A bench drill press uses stepped pulleys or a VFD to give 250-3,000 RPM.
- Clutch (cordless only): Limits torque transmitted to the bit by slipping a spring-loaded ratchet. Settings 1-15 or so on a typical drill correspond to roughly 4-40 N·m. Set it lower than your hand can resist, or a bound bit will snap your wrist when it grabs.
- Feed mechanism: On a drill press, a rack-and-pinion quill delivers controlled feed — typically 0.05-0.3 mm per revolution depending on bit diameter. On a hand drill, the operator's body weight is the feed mechanism, which is why hand-drilled holes in metal are often inconsistent without a pilot hole.
Where the Drill (general) Is Used
Drills exist in every workshop because round holes are the most common feature in mechanical assemblies. The mechanism scales from watchmaker's pivot drills running at 20,000 RPM on a 0.3 mm bit, to magnetic base drills running at 250 RPM on a 50 mm annular cutter through a structural I-beam. What changes between applications is the spindle stiffness, the RPM range, the feed control, and the bit material — but the physics of two cutting lips shearing a chip stays identical.
- Construction: Hilti TE 6-A36 SDS-Plus rotary hammer drilling 12 mm holes in concrete for anchor bolts on commercial fitouts.
- Metal fabrication: Milwaukee M18 FUEL Mag Drill running a 22 mm Slugger annular cutter through 20 mm structural steel plate for bridge gusset connections.
- Woodworking: Festool DF 500 Domino joiner — a specialised drill that cuts mortises rather than round holes, used in cabinet shops for face-frame joinery.
- Aerospace assembly: Boeing 787 wing skin assembly using pneumatic positive-feed drills with carbide bits to drill 6.35 mm fastener holes through CFRP/titanium stacks.
- Dentistry: NSK Ti-Max Z95L turbine handpiece running diamond burs at 200,000 RPM for cavity preparation in tooth enamel.
- PCB manufacturing: Schmoll high-speed CNC drilling machines running 0.15 mm carbide bits at 200,000 RPM to produce via holes in multilayer printed circuit boards.
The Formula Behind the Drill (general)
The fundamental equation for any drill is the conversion between surface cutting speed at the bit tip and spindle RPM. Get this wrong on the low end and the bit rubs and dulls within a few holes. Get it wrong on the high end and the cutting edge overheats, anneals, and burns. The sweet spot is the recommended surface speed for the bit material and workpiece combination — for HSS in mild steel that's around 30 m/min. Below 15 m/min you waste time and polish-harden the work. Above 50 m/min you'll see blue chips and a burned point within seconds.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| N | Spindle rotational speed | RPM | RPM |
| Vc | Surface cutting speed at the bit's outer edge | m/min | SFM (ft/min) |
| D | Bit diameter | mm | in |
| π | Pi, geometric constant | — | — |
Worked Example: Drill (general) in drilling stainless steel in a marine fabrication shop
A marine fabricator is drilling 8 mm clearance holes for M8 stainless bolts through 6 mm 316 stainless steel plate to mount a deck cleat. The bit is a 135° split-point cobalt M35 twist drill in a Milwaukee M18 FUEL drill press. Recommended surface cutting speed for cobalt in 316 stainless is 18 m/min nominal, with a usable range of 10-25 m/min depending on coolant and feed.
Given
- D = 8 mm
- Vc,nom = 18 m/min
- Vc,low = 10 m/min
- Vc,high = 25 m/min
Solution
Step 1 — compute spindle RPM at the nominal cutting speed of 18 m/min for cobalt in 316 stainless:
Step 2 — at the low end of the usable range, 10 m/min, which is what you'd run dry without coolant or on a flexible setup where chatter is a concern:
At 398 RPM the bit cuts cleanly but slowly — you'll feel solid chip formation and minimal heat at the bit shank, and a 6 mm deep hole takes about 8-10 seconds at a sensible feed. This is the safe setting for a hand-held cordless drill where you can't guarantee straight feed.
Step 3 — at the high end, 25 m/min, only achievable with flood coolant on a rigid drill press:
At 995 RPM the same hole goes in 3-4 seconds, but you must have constant coolant flow and aggressive enough feed (around 0.15 mm/rev) to keep the chip thick — otherwise the bit rubs, the 316 work-hardens to roughly 40 HRC, and the next bit you put in won't cut at all.
Result
Set the drill press to roughly 700 RPM for the nominal case. That's the sweet spot — cobalt cuts 316 stainless cleanly, chips come off blue-grey and curled, and the bit lasts 50-80 holes before resharpening. At 398 RPM you trade time for tool life and forgiveness; at 995 RPM you trade tool life and risk for cycle time. If your measured hole quality drops below predicted — bit dulling fast, hole oversized, or chips coming off as fine powder instead of curls — the most common causes are: (1) feed rate too light so the bit rubs and work-hardens the 316 surface, (2) chuck runout above 0.1 mm causing the bit lips to cut unevenly, or (3) point angle ground to 118° instead of the 135° split point needed for stainless, which lets the bit walk and skate before it bites.
When to Use a Drill (general) and When Not To
The drill family is wide. Picking the right type matters more than picking the right brand. Here's how the three most common shop-floor options compare on the dimensions that actually drive the buying decision.
| Property | Cordless drill (18V) | Drill press (bench) | Magnetic base drill |
|---|---|---|---|
| Max RPM | 2,000 RPM | 3,000 RPM | 750 RPM |
| Hole accuracy (positional) | ±1-2 mm freehand | ±0.2 mm with vise | ±0.3 mm on steel |
| Max practical bit diameter in steel | 13 mm twist | 16 mm twist | 50 mm annular |
| Cost (typical pro tool) | $200-400 | $300-1500 | $1500-3000 |
| Portability | Fully portable | Bench-mounted | Portable on ferrous workpiece |
| Best application fit | Site work, screw driving, small holes | Repeatable shop holes in small parts | On-site structural steel and beams |
| Spindle runout (typical) | 0.1-0.2 mm TIR | 0.05-0.1 mm TIR | 0.05 mm TIR |
Frequently Asked Questions About Drill (general)
Almost always feed rate, not speed. Stainless 304 and 316 work-harden if you let the cutting edge rub instead of bite. If your feed is too light — say, under 0.05 mm/rev on an 8 mm bit — the lips skate across the surface, raise the local hardness from roughly 200 HV to over 400 HV, and the next pass of the same lip is now cutting hardened steel.
Diagnostic check: look at the chip. If you're getting fine grey dust or short broken flakes, you're rubbing. You want continuous curled chips coming off blue-grey. Push harder — stainless rewards aggressive feed.
118° is the general-purpose grind and works fine for wood, plastics, aluminium and mild steel when you've got a centre-punched start. The flat-ish point needs a divot to stop it walking.
135° split point is what you want for stainless, hardened steels, and any time you can't centre-punch — sheet metal, curved surfaces, hand-held drilling. The split point self-centres because the chisel edge is broken into two short cutting edges that bite immediately. Rule of thumb: if the workpiece is harder than 200 HB, or the surface isn't flat and punched, use 135°.
Three suspects in order of likelihood. First, chuck runout. Spin the bit slowly by hand and watch the tip against a fixed reference — if you see more than 0.1 mm of wobble at the tip, the chuck jaws are worn or the bit shank isn't seated square. Re-tighten the chuck in three positions 120° apart to even out the jaw clamping.
Second, lip length asymmetry on the bit. If one cutting lip is even 0.05 mm longer than the other, that lip cuts a wider arc and the hole comes out oversize. This happens on hand-resharpened bits. Use a drill bit grinder or buy a fresh bit.
Third, no pilot hole on a large bit. Anything above about 8 mm wants a 3-4 mm pilot first, otherwise the chisel edge bulldozes material and the bit wanders before it bites.
Three triggers. One: hole positional tolerance tighter than ±0.5 mm — a hand-held cordless cannot hit that consistently no matter how steady you are. Two: bit diameter over about 10 mm in steel, because the torque reaction will twist your wrist when the bit breaks through. Three: more than about 20 holes in a batch — the drill press repeats RPM and feed exactly, where freehand variation kills bit life and consistency.
For one-off site work, structural anchor holes, or driving screws, the cordless wins on portability every time. The two tools do different jobs.
Classic flute-grab. As the cutting lips exit the back face, the chip has nowhere to form against, and the helical flutes try to screw the bit forward into the work like a wood screw. On thin material or soft metals like brass and aluminium this can yank the drill out of your hand or snap a small bit at the flute root.
Two fixes. For brass, regrind the leading edge of the flute to a 0° rake (a small flat ground onto the cutting face) — this stops the bit self-feeding. For everything else, ease off the feed pressure in the last 1-2 mm of breakthrough and back the workpiece with a sacrificial board so there's material under the exit face. Setting the cordless drill's clutch a click or two below stall torque also limits the damage if it does grab.
Different mechanisms, different jobs. A hammer drill (cordless, like a DeWalt DCD996) uses two ridged clutch plates that ratchet against each other to deliver a few thousand light axial blows per minute. Fine for occasional 6-10 mm holes in soft brick or mortar, useless in poured concrete.
A rotary hammer (like a Hilti TE 6) uses a piston-driven pneumatic mechanism that delivers genuinely hard blows — 2-3 joules per impact versus a few hundredths for a hammer drill. This is the tool for concrete, drilling 12-25 mm anchor holes all day.
An impact driver doesn't hit axially at all — it delivers rotational impacts via a spring-loaded hammer-and-anvil. It's a fastener tool, not a hole-making tool. Don't try to drill with one unless you've got hex-shank impact-rated bits, and even then it's a compromise.
References & Further Reading
- Wikipedia contributors. Drill. Wikipedia
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