A cordless impact driver can be used like a very fast drill for driving screws and other fasteners, as well as for drilling holes. When extra power is needed an impact driver can deliver much higher torque than a typical drill diver. (300-500 in-lbs of torque vs. 1200-1500 in-lbs!)
Thanks to the hammering-action of the impact mechanism, the bit is turned with quick, forceful impacts making it less likely to strip a screw head. Due to the design of an impact driver, there is very low-recoil on your wrist and arm. One handed operation on even the toughest screws is easy.
[Update: Oct 14, 2012 – See this cool video from DIY network that looks at the internals of a right-angle driver in slow-motion. It’s a bit of an ad for the Craftsman Nextec. but it’s cool nonetheless.]
The higher torque and speed puts additional stress on the screw, so you can over-drive or shear off screws much easier – as well as break driver bits that aren’t rated for impact.
Instead of a keyed chuck, a typical cordless impact driver has 1/4″ hex bit socket. With this it’s simple to quickly swap bits – in many cases, one handed. They are much more compact than drills as well – usually 3-5 lbs including the battery, and 3 or 4 inches shorter. Working in tight areas is much easier with one!
If you are looking to drive screws or bolts, and you need the flexibility of a battery powered tool, a cordless impact driver is a great solution. Now that you know what you need, what are the things to look for when choosing among all the available options?
- torque - This is the amount of turning force that can be applied to the fastener. It can range from around 500 in-lbs in the low voltage models, up to over 1,600 in-lbs. A higher torque means a larger range of applications you can tackle with your driver. It also means a higher incidence of shattering bits, so make sure you use impact-grade accessories!
- weight - Due to their nature, impact drivers are already much smaller and lighter than the regular drill counterparts. The low weight makes them easy to use with less fatigue. However, because of the internal hammering impacts, if the weight is too low, you may feel vibrations that can become uncomfortable over time. If this is a concern, try to keep to models weighing upwards of 3 pounds.
- voltage - Generally speaking, the higher the voltage, the more powerful the tool. If you are looking for something small, check out the 12 volt models; for something to handle medium to large projects, 18 volts is what you probably need.
- battery - Some models use their brand's NiCAD/NiMH batteries, others are Lithium Ion, while others allow both types of batteries to be used. See here for a comparison of battery types. We try to explain which batteries are acceptable for each driver we review.
- physical size - If you are installing decks or other installations with hundreds of fasteners, you need a tool that will fit comfortably in your hand. Working overhead a lot? A small and lightweight driver will keep fatigue away. Plumbers or other workers in tight spots will want to get a short-profile driver to get as much working room as possible. Think about how you'll use the cordless impact driver the most, and what will be best in those situations. New users beware - you will end up using this tool in far more ways than you expect!
- speed - Speed ratings have 2 components - revolutions per minute (rpm) and impacts per minute (ipm). Higher impacts roughly translates into higher torque, allowing the speed to stay high. And high speed means more work done in less time! [box type="info"]Manufacturers generally give RPMs values when the tool is operating with no load.[/box]
- brand name - While some brand names come at a premium price, sometimes there's a reason for it. Some brands offer longer warranties or have a reputation built around their repair services - allowing you to keep an old tool instead of replacing it! We will note all warranties we are aware of at the time the review is posted.
- extras - Sometimes you may find that a smaller feature may be final deciding factor between two similarly rated drivers. Variable speed triggers, direction switches, forward lights are some of the extra features an impact driver may have. Comfort grips, belt hooks, and additional speed controls are other extras that aren't available on every impact driver.