The speed of a cordless impact driver is measured in RPM (Rotations Per Minute) – one full turn of the chuck is one rotation. A tool’s maximum ‘no-load’ speed will be presented as a number followed by ‘RPM’. The higher the number, the more rotations the chuck can complete in one minute, and the faster it can turn the screwdriver bit or drill bit.
What is the maximum ‘no-load’ speed?
When selecting a cordless impact driver, you will find that manufacturers usually give the tool’s maximum ‘no-load’ speed.
This is the maximum speed at which the chuck can turn without a load (when it’s switched on and the trigger is completely pulled in but it’s not driving screws or drilling holes).
Manufacturers give the tool’s speed at no-load because once the impact driver begins driving screws or drilling, its maximum speed will vary depending on the load (the size of the screw and the type of material).
When working with very large screws or tough materials, the cordless impact driver may slow down as it struggles to overcome the resistance. By exactly how much will depend on the particular task at hand.
How many RPMs do you need?
Most cordless impact drivers have a maximum no-load speed of around 2,500 RPM. To put this into perspective, the average cordless screwdriver can deliver 200 RPM and the average cordless drill driver can deliver 1000 RPM.
Quite simply, a cordless impact driver with a higher maximum speed will be able to complete the same task in less time than one with a lower maximum speed. However, the higher the speed, the more expensive that particular model is likely to be.
If you are completing a personal project, the speed at which you carry out the work may not be an overriding factor. On the other hand, you may be relied upon to carry out work quickly, and so more RPMs will be a priority.
Varying the speed
The speed of a cordless impact driver is varied using the speed control trigger.
Squeezing the trigger starts the chuck turning. The further you pull the trigger in, the faster the chuck will turn and the more torque the tool will deliver. The more you release the trigger, the slower the chuck will turn and the less torque the tool will deliver. Releasing the trigger completely will stop the tool.