How an impact driver works
When it comes to driving screws, you just can't beat the speed and raw power of a cordless impact driver.
Since I had a large deck to build, I figured it was a perfect opportunity to buy the new—and very radical looking—Hitachi WH18DFL 18-volt lithium-ion impact driver.
Unlike electric drills or cordless drill/drivers, impact drivers are specifically designed to do one job: drive screws.
And they do it better and faster than any other tool.
Here's how:
Impact drivers use both bit rotation and concussive blows to hyper-drive screws through the toughest woods.
The result of this two-punch combination is unparalleled, Herculean screw-driving power: The typical 18-volt drill/driver produces about 500 to 550 inch-pounds of torque.
The new Hitachi delivers an amazing 1,150 inch-pounds of torque.
Despite that impressive power surge, the Hitachi is very easy and comfortable to use because the concussive blows—hammering out at a rapid-fire 3,000 blows per minute—transfer all that amped-up torque directly to the screw, not your wrist.
Impact drivers can also be used to drive lag screws and to tighten hex-head nuts and machine bolts. However, I discovered that there was a way to double the tool's usefulness and versatility.
Hitachi sells a 3/8-inch keyless 3-jawed chuck accessory for about $40 (part no. 725405) that snaps into the tool's collet, allowing you to quickly switch from screw driving to hole drilling.
The WH18DFL comes with two lithium-ion batteries, a charger and storage case; it has a list price of $393, and normally sells for about $220, but I got a great deal online for only $167.
More:
Makita's 18-volt impact driver, a snub-nosed wonder.
(6) Comments
Your deal link is broked.
I always seem to have more problems stripping the head on a screw than my drill not being able to drive it. Is an impact driver less likely to strip the heads?
Well, Jim, stripping screw heads is pretty common when power-driving screws with a standard electric drill, but it shouldn't happen when using a cordless drill/driver. Adjust the slip clutch on the tool to match the size screw and hardness of the wood. (And check to make sure it's not in the "drill only" mode.)It may take a little experimentation, but after two or three attempts, you should be able to find the right setting that allows you to drive in the screws without damaging the heads.
When properly set, the clutch will "slip" allowing the motor to keep running while the bit stops turning, just as the screw contacts the wood.
And, yes, an impact driver is much less likely to strip screw heads, even though it doesn't have--or need--a slip clutch. The combination of bit rotation and concussive blows provides improved screw-driving power, but requires less muscle from the user. It's one of those things that's hard to explain, but very easy to experience first hand. Go borrow an impact driver and check it out for yourself. I think you'll be pleasantly surprised!
What about removing stubborn screws and you are afraid of stripping the screws? Is it more or less likely to strip the screw when using the impact driver?
When looking at drills and drivers one can find then in various Voltage - how much of a difference is there between a 14v and an 19v drill/driver?
My husband has been looking into buying an impact driver. I am still trying to figure out what the difference between a drill and an impact driver are and stumbled on to your article. From the article it sounds like impact drivers are less likely to strip screws and for that reason alone I am convinced we need one. That seems to be our problem constantly. I think we will take your advice and borrow one before we go out buy one ourselves.
Regarding screws stripping: With a drill, typically it's the phillips screws that strip, because of the bit's tendency to "cam-out" of the head (that is, to climb up and out of the head and spin freely). This forces you to put push hard on the drill to keep the bit engaged.
With an impact driver, the torque is delivered in distinct bursts, with pauses in between. These pauses allow the bit to fall back into the head before it can climb all the way out. Also, when hitting a knot, instead of the torque ramping way up like with a drill, the speed just slows down and the hammering continues.