Eugene is a trained engineer and self-taught home improvement enthusiast with almost 40 years of professional and DIY experience.
What Do the Number Mean on a Cordless Drill?
Cordless tools are great and, unlike their corded counterparts, they have the obvious advantage of freedom from a power cord that can get in the way, become taut when maneuvering the tool or end up being tripped over. Also you don't have to be lugging extension leads around.
A power drill is probably one of the most useful cordless tools, but unlike the corded version, you've probably discovered it has lots of numbers around the chuck and maybe a switch with the numbers "1" and "2" marked beside it? So what are these for?
In this guide, I'll explain how and why these settings are needed and when you can use them to drill or drive screws more effectively. There's a little bit of background information first about torque that you might like to read, or you can skip straight to the section on how to use the settings on your drill.
What Is Torque?
Both of the adjustments on a cordless drill are connected with a physical quantity known as torque. Torque is like the rotational equivalent of force. So when you push something, you're exerting a force, but if you twist the handle on a tap/faucet, you're exerting a twisting version of that force, known as torque.
Imagine if you have two forces acting opposite to each other but not in line (see diagram above) We call this a couple. Here's a little maths, stay with me because it's quite simple! If the distance between each force F is d, then the magnitude of the couple is called the torque = Fd (I.e. F multiplied by d).
Bigger forces, i.e. if F is larger, means greater torque. Also, increasing the distance between the forces (d in the diagram) also increases torque. This is why long handles on tools such as socket wrenches give more turning force. Gate valves, like the one in the photo below, for turning flow on and off in pipes, have large diameter handwheels for the same reason.
What Are Gearboxes?
These mechanisms are used in machines and vehicles as torque and speed converters. At the most basic level, a gearbox is just two cogs of different sizes, one gear turning the other. In practice, however, a gear box can utilise lots of gears (such as the one in a manual transmission car) allowing varying speeds.
One function of a gearbox is to increase torque, but the downside is that rotational speed is reduced. However this doesn't necessarily matter because the increase in torque is what's important. When a small gear drives a bigger gear, the shaft that the bigger gear is connected to produces more torque. Similarly, a bigger gear driving a smaller gear results in a higher rotational speed, but less torque. In a vehicle, the lowest gear would be used to increase torque to produce a lot of force at the wheels to get the vehicle moving. Without a gear box, a more powerful engine would be needed to generate this torque.
A gearbox can also do the reverse, i.e increase speed. An example is the gearbox on a windmill for turning the generator much faster than the the vanes of the windmill. The whisks of an eggbeater also spin much faster than the handle is turned. When speed is increased, torque is reduced, but again it's the increased speed that's desired and the reduction in torque may not be a problem.
A common misconception is that more torque = more power. However, this isn't necessarily so. Reduction gearing for instance produces more torque, but it also reduces angular rotation speed and since power = torque x angular velocity, the power stays the same. Torque is measured in Newton metres (Nm) or foot pounds (ft.lbf).
Setting 1: Adjusting the Clutch on a Cordless Drill
The first setting on a cordless drill, adjusted by turning the numbered ring, is for varying the torque level above which the clutch slips.
How does the clutch work?
The motor on a drill drives the chuck, the part of the drill that holds a drill or screwdriver bit. Between the motor and chuck, inside the drill, is a mechanism called a clutch.
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A clutch, just like the one on a manual shift car, is simply the mechanical equivalent of an electrical switch. It either transmits power along a shaft or it doesn't. In the case of a cordless drill, if a drill bit gets stuck in a workpiece or a screw suddenly becomes hard to turn as it's driven home into timber, the clutch will slip, disengaging the motor from the chuck.
The motor continues to spin, but it just doesn't turn the chuck. By turning the numbered ring, you can adjust the torque level or twisting force at which the chuck will slip.
When to adjust the clutch setting.
The control ring with "1", "2", "3" and larger numbers (A) is for setting the torque limit of the clutch. The clutch allows the chuck to slip when the motor tries to twist it with a torque level that's above a limit set by the position you've turned the control ring to. You can use this for example to prevent over driving screws into soft timber (which could bury screw heads and crack timber).
Start with e.g. the control set 1/3 of the way up (position 5 if there's 15 positions). If the clutch slips and screws don't end up flush with timber, increase the setting. Also if you're drilling using very small bits, setting this to the lowest value possible prevents bits snapping if they get stuck (which can happen when drilling metal as the bit breaks through to the other side and snags)
Setting 2: Changing Gears
The second setting is a slide switch for changing gear. Usually there are two gears, "1" is low gear and "2" is high gear. Some drills have 3 gears, allowing finer control of torque/speed.
Low gear gives you higher torque (twisting force) and lower speed for drilling screws or using large diameter drill bits. High gear gives lower torque and higher speed and is better for smaller drill bits and fast drilling, or using accessories that work better at high speed (e.g. mounted points for grinding).
Setting 3: Screw, Drill or Hammer Action
The third setting on a combi drill is for turning on hammer action for drilling masonry. Usually there are three different positions on this ring:
- Screw symbol: For driving screws. The clutch slips depending on the torque setting as explained earlier.
- Drill bit symbol: The clutch doesn't slip.
- Hammer symbol: Hammer action for drilling masonry with tungsten carbide tipped masonry bits.
I normally don't use the setting with the drill symbol when drilling. Instead I choose the screw setting because I think it's better to be able to set a torque limit to stop drill bits getting broken, which can easily happen if they have a small diameter.
Setting 4: Switching Between Forward, Reverse and Neutral
This is simply for changing the direction of the chuck.
- Forward for driving screws/drill bits.
- Reverse for extracting screws, releasing drill bits/screwdriver bits from the chuck or reversing drill bits out of the material being drilled if they can be pulled out.
- Neutral. Leave the drill in this position to stop it tuning on if the trigger is inadvertently squeezed.
It's a good idea to remove the battery from your drill in storage. Some drills allow you to partially slide and disengage the battery from the battery terminals, while it still remains attached to the drill.
Is the Torque Spec of a Drill Important?
It depends on the application. If you're drilling small diameter holes in wood, plastic or metal, it's not so important. However, if you're using large diameter drills, there's more friction between the drill bit and material being drilled. This is when more torque is better, because it overcomes friction.
Another application where torque is important is when drilling long screws into timber, especially if the screws are large diameter, such as TEK screws for holding metal cladding onto a stud wall or roof, e.g. when building a shed.
Cordless impact drills
Impact drills are available and can produce much higher torque than a standard cordless drill/driver. These drills basically use a hammer action when driving screwdriver bits. (This is rotational hammer action as distinct from the axial hammer action on a masonry drill which pushes the bit backwards and forwards for drilling concrete/stone) This type of drill doesn't have a chuck and is used with impact rated screwdriver bits.
Manufacturers usually quote a soft and hard torque for a cordless drill. The soft torque is the maximum value of torque when the drill is turning a screw bit or drill bit. Hard torque is the torque impact magnitude when a screw is driven home and the chuck approaches stall.
Torque on cordless drills is measured in Newton metres (Nm) or foot pounds (ft.lbf) in the US.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2022 Eugene Brennan