Speed vs Torque in Drills and Impact Drivers
New Pros and apprentices can benefit from some quick tips on how the speed vs torque differs between drills and impact drivers. It’s more than just a difference of how to set the mode. Speed and torque change very differently from one mode to the next on these two tools. The good thing is that it’s easy to keep straight once you understand how they work to optimize drilling and driving.
Quick Article Summary
- Drills are for making holes
- Impact drivers are better at handling tough fasteners
- Impact drivers produce more torque and speed with higher modes
- Drills have “inverse” power modes—more speed equals less torque and vice versa
Speed vs Torque Applications for Drills and Impact Drivers
Drills do their best work making holes. Period. Whether using a standard twist bit, spade bit, or even a hole saw, the smooth power transfer makes for cleaner holes than you get with the “violence” of an impact driver. The one exception comes when you want consistent or smooth speed with fasteners not prone to stripping. In this case, a drill delivers faster driving speeds at the expense of “reactive torque”.
What is Reactive Torque?
Reactive Torque occurs because the drill motor is driving the chuck and fastener in a clockwise rotation while the drill itself (since it’s anchored to that motor) wants to spin equally hard in the opposite direction. You feel this as a user holding onto the drill and it’s your leverage that keeps the drill from just spinning in the opposite direction.
An impact driver excels at driving fasteners. This is largely thanks to higher torque and a hammer/anvil mechanism that delivers consistent driving speeds. It does so without the reactionary torque to your wrist while driving—even with heavy-duty fastening tasks. When you use these two tools as a one-two punch, you can really shave some time off jobs that include both drilling and driving tasks.
Speed vs Torque and Brushless Motors
At first, multiple speed drills and impact drivers both changed gears using a mechanical switch on top of the tool. Brushless motors introduced electronics necessary for the motor, so manufacturers started adding electronic mode controls as well. Now, we see drills continuing to use the standard mode switch while impact drivers use electronic mode buttons. These are typically located either above the battery or on the top of the tool.
When you switch modes, different things happen depending on which tool you’re using. Arguably, the impact driver is easier to follow. As you go from lower to higher speeds, both the speed of rotation (RPMs) and torque (in-lbs) increase. The higher the Mode, the faster and more powerful the result. You typically find Pros using lower modes for small finish carpentry screws and switching to higher modes for driving construction fasteners.
With drills, however, speed and torque are reversed. In Low speed (or Mode 1), the drill can deliver every possible inch-pound of torque. High speed delivers more RPMs but drops the available torque. You may find that you can drive screws in High speed, but have to switch to Low for tougher jobs. That may include using a large ship auger bit or even drilling with larger hole saws.
Why the difference?
An impact driver gives you access to more power as you go from Low to High speed. A drill gives you access to most of its power in both modes. However, in order to transfer more torque when needed, it takes that power away from the rotation speed. When speed is more critical, you can opt for the higher RPM mode and the tradeoff of a reduction in torque.