Two measurements, two ideas
RPM stands for revolutions per minute: how many full turns the chuck, blade or bit makes in a minute. It tells you how fast something spins.
Torque is the twisting force the tool can apply. It tells you how hard the tool can turn against resistance. Torque is measured in units such as inch-pounds, foot-pounds or newton-meters.
A bicycle gives a good picture. In a low gear you pedal fast but the wheels turn slowly, and you can climb a hill. In a high gear each pedal turn moves you farther, but starting uphill is hard. A tool’s gearing works similarly: you can often have more speed or more twisting force, but not the most of both at once.
How speed and torque are linked
The power a motor can deliver is limited. Roughly speaking, the amount of work a motor can do each second is related to speed multiplied by torque. So within a given motor, if the gearing makes the chuck spin faster, the torque available at the chuck is lower, and if the gearing makes it spin slower, the available torque is higher.
That is why many drills have a two-speed gearbox:
- Low gear. Slower, with more twisting force. Useful for driving screws, using large bits and starting holes in tough material.
- High gear. Faster, with less twisting force. Useful for small bits and light drilling.
Check your manual, because the switch position and the labeling vary. Do not change the gear selector while the motor is running unless the manual says it is acceptable.
No-load speed is a maximum
The RPM on the box is normally the no-load speed, meaning the speed with nothing cutting or turning. When the bit meets resistance, the speed drops. A tool that lists a high no-load speed does not necessarily cut better, and it does not mean the tool has more torque. Comparing two tools means looking at both figures, and noting how each is measured.
Trigger and dial speed control
Two kinds of speed control are common.
- Variable speed trigger. The harder you squeeze, the faster it turns. This lets you start slowly, then speed up. Good variable speed control helps you start a hole without wandering and ease a screw into place.
- Speed dial. A numbered dial that sets a maximum speed. Common on routers, rotary tools, sanders and some drills. It is useful when a particular speed is recommended for the bit or accessory.
A speed dial does not usually have exact RPM values, and the numbers represent relative levels. The manual may give a chart linking dial numbers to RPM ranges.
Matching speed to the job
Some general principles, not exact rules:
- Larger diameter means slower speed. The edge of a large bit or cutter travels much faster than the edge of a small one at the same RPM. Large router bits, hole saws and big drill bits are often run at lower speeds to avoid overheating, burning the cut, or losing control.
- Harder materials generally mean slower speed. Drilling metal is usually done at low to moderate speed, with steady pressure and often a lubricant or cutting fluid. Too much speed overheats the bit and dulls it quickly.
- Softer materials tolerate more speed. Small bits in softwood are often run faster, though burning can still happen.
- Plastics melt. Moderate speed and sharp bits are the usual approach.
- Masonry. Rotation is usually slow, with hammering action when the tool has it.
- Sanding and polishing. Lower speeds for finishing compounds and plastic. Too much speed can generate heat and damage the surface.
Manufacturers of bits, blades and accessories often publish recommended speeds or speed ranges. If the packaging gives one, follow it. The type of bit also matters, as different drill bit types are designed with different cutting geometries, and saw blade types have limits tied to their size and design.
Torque in driving and fastening
For driving screws, torque matters more than speed. A larger or longer screw, or a dense material, needs more torque to seat. A drill with a clutch can limit that torque to avoid overdriving, and an impact driver delivers bursts of rotational force that can be useful for long fasteners. Torque control is also central to fastening bolts to a specified tightness, where a torque wrench is set to specific torque settings.
When a tool stalls
Stalling occurs when the load exceeds the torque available, so the motor slows or stops. Signs include a falling pitch, a smell of hot windings, or the chuck refusing to turn. If a tool stalls:
- Release the trigger and stop.
- Back the bit out gently, and do not force it.
- Check whether the bit is dull, the hole size is too large for the tool, or the gear selection is wrong.
- Let the tool cool if it feels hot.
Keep a firm grip, use a side handle if provided, and be ready for a sudden twist if a large bit snags. Clamp your work so it cannot spin.
Quick reference
- Slow and strong for big bits, screws and tough jobs.
- Fast and light for small bits in softer material.
- Start slowly, then build speed.
- Read the recommended speed for the accessory.
- A high RPM number is not a promise of more power.