Singin' the impact driver blues
June 18, 2008 8:51 AM   Subscribe

My recently purchased impact driver strips the heads of screws. Is this normal?

Several months back, I bought an 14.4 volt Hitachi impact driver, along with a 20-piece set of screw and drill bits.

Invariably, after driving a screw, I'm left with a few iron filings attached to the magnetic end of the bit. If I unscrew the screw several times, and drive it back in, I'm down to a screw with a gaping hole in its center--an unreusable screw.

Is this normal with impact drivers? Am I using the wrong driving technique--or attachable screw bit?
posted by Gordion Knott to Home & Garden (19 answers total)
Usually, this means you're not applying another pressure and the bit is moving within the screw head. Is that happening?

Does your driver have a torque setting? It should not be at the max for screws.
posted by JMOZ at 8:58 AM on June 18, 2008

In addition to making sure you are using the right torque setting (which should be pretty low for working with normal screws) and not spinning the bit without good contact with the screw head, you should make sure that you are using the right screws to use with a high-powered drill or driver. I tend to use the gold (colored)-plated screws for everything, as their heads will stand up to a lot more and they will hold a hell of a lot.

I also don't really use an impact driver for working with screws; I usually only pull it out to try to extract a frozen screw or to drill through masonry or something like that. Good luck.
posted by iknowizbirfmark at 9:05 AM on June 18, 2008

JMOZ, don't know about the torque setting, but if the trigger is pushed in half way the head rotates at slow speed, like a normal chargeable screwdriver, without the brrrt! air-gun noise.
posted by Gordion Knott at 9:05 AM on June 18, 2008

Impact drivers aren't for nice little jobs. They're the equivalent of a power washer, where a regular drill is a garden hose. Is there a way to lock out the *impact* part of the drill, and make it a regular drill?
posted by notsnot at 9:07 AM on June 18, 2008

Joining the party to say the impact drill isn't for everyday screw activity. Depending on what bits you have, you could pick up some square head screws instead of phillips head and give those a try.
posted by shinynewnick at 9:13 AM on June 18, 2008

Impact drivers typically don't have torque settings, they build up torque with each successive 'blow'. They can easily sheer off bolts/screws/bits if you aren't careful. Make sure you are using the correct bit, and don't just go full speed, you need to back off a bit at the end. It's not like a driver drill that has a clutch, it will just keep on thwacking the screw until it breaks (and it wont slip out either because of the hammer action)
posted by zeoslap at 9:16 AM on June 18, 2008

There is a quick vid of me having some fun with an impact driver here first time I tried unsticking these bolts the driver completely sheared off a brand new Bosch flat head bit. These things definitely pack a punch :)

I wouldn't say they only for tough jobs either; as long as you go easy on the trigger they are great for even lightweight jobs.
posted by zeoslap at 9:26 AM on June 18, 2008

Are they drywall, wood screws or machine screws? And what material are you screwing the screws into? Make sure you have the right screw for the right application.

Typically, drywall screws have little shear strength, wood screws have more and machine screws will have the most. In my experience, impact drivers are great for the right application, ie screwing long wood screws through medium to soft wood, thin gauge metals together with self tapping or drill point screws, screwing cabinets together so you dont have to countersink them, etc...anywhere you need a lot of torque, to start screwing through hard stuff, or power through a lot of material.

If you need to adjust or loosen/tighten the screw constantly, then I suggest getting a screw gun with an adjustable clutch. It lets the clutch slip instead of the bit skipping out of the screw and stripping the head.

Good luck.
posted by MiggySawdust at 9:42 AM on June 18, 2008

>Are they drywall, wood screws or machine screws? And what material are you screwing the screws into?

Wood screws into wood. I've tried driving the screws without pilot holes, but lately I've reverted to drilling a pilot hole first.

Should I be drilling pilot holes for wood screws into wood?
posted by Gordion Knott at 9:58 AM on June 18, 2008

You should, esp. for thin boards. But again, I think you're using the wrong tool. A drill (no impact) with a clutch is what you need. The impact *sounds* cool and all, but it's for un-sticking engine parts.
posted by notsnot at 10:01 AM on June 18, 2008

As others have noted, the impact wrench is probably not the right tool for the job you're describing. With wood and wood screws, I use my impact wrench only for long screws to reduce binding. (Or when I'm in a hurry and lazy and only have one or two screws to work and the wrench is more convenient to grab -- otherwise I always use a drill or screwdriver.)

The impact wrench spins the motor mass to build up stored energy, then connects it suddenly to the shaft to generate a high-torque impact. When you work with something springy (like a screw in wood), the impact will drive the screw in a little. When the wrench releases the shaft to spin the motor mass, the spring effect in the wood/screw can cause the shaft to rotate backwards. This is an effect you can actually see as you're driving the screw.

If you have to use the impact wrench, make sure you have the shaft aligned with the shaft of the screw as perfectly as possible. Maintain enough pressure to keep the bit well-seated in the screw head and use a light finger on the trigger. If you drive the screw and then take it back out with the wrench, discard the screw and get another -- chances are you've stripped enough metal off the head that it will be hard to work with later on.

Pilot holes are good to prevent splitting or when you need a third hand to help steady the screw.
posted by joaquim at 10:36 AM on June 18, 2008

You should generally drill pilot holes into wood, yes, because the volume of the screw is generally pretty considerable, and the space it occupies used to be occupied by wood, which has to go somewhere. Typically this leads to splits, or mushrooming (it drives the wood out from the face of the board).

I love square drive screws because they're nearly impossible to strip. *Nearly*. You can get them from McFeely's and they come in all shapes and sizes and what not. I buy "sets" whenever I need screws, which are 100 each of common sizes. They come with nice bins to store them all in, also, and typically a few drill-drivers and manual drivers. They also have pretty cheap "sample" sets which are 25 or so of a lot of different sizes of screws.
posted by RustyBrooks at 10:41 AM on June 18, 2008 [1 favorite]

I have that 14.4v Hitachi. And the 18v. They are BEASTS. If you're stripping the heads then you're doing something wrong...anything from too-soft-screws to not pressing in hard enough.

I used this drill for the entire buildout of a store, everything from drilling through concrete to putting screws in wood to putting self tapping metal screws into 1/2" steel girders.

Go slow and press hard.

Make sure you have the right size bit, too. You want that bit to fill up the space in the head of the screw, not just fit in it.
posted by TomMelee at 10:57 AM on June 18, 2008

The variable speed you mention and the clutch are two separate features. The clutch limits the torque to a certain (variable) amount and will slip with an audible clicking sound when that point is reached to prevent stripping the screw head or driving the head too far into the wood. This is independent of speed. Typical clutches have numbered settings on a plastic collar around the chuck.

Try pushing more firmly on the screw as you drive it in, and back off on the trigger when the head is flush with the wood (or let the clutch do that job). If the wood is hard you should drill a pilot hole for ease of entry and to prevent the wood from splitting. The pilot drill bit should be the diameter of the solid center of the screw, not the width of the threads; this will allow the threads to bite. You can also get special bits that will drill a pilot hole and finish off with a shallow tapered hole to countersink the screw head.

"Square" head screws are called Robertson. They have the advantage of not stripping as easily, and you can put them on the driver before drilling and they will stay there. "Cross" heads are called Phillips (see chart halfway down page on right).
posted by weapons-grade pandemonium at 10:57 AM on June 18, 2008

1. Impact drivers have been over-sold to the home market as powered drivers, I feel. As others have noted, they have very high torque with no torque-limiting mechanism. They're very powerful drivers, much smaller and lighter than cordless drills. While this is probably great for construction pros, it's not so great for the layperson building a deck or something. It's very easy to strip heads, as you've noticed.

I much prefer a cordless drill with a clutch for these jobs. I can set the resistance so my inexperienced hands don't rip the screwheads into the wood and don't strip the head patterns. They're heavier and perhaps slightly slower, but drills allow a lot more control.

2. For larger-shank traditional wood screws, pilot holes are necessary. The narrow-shank deck screws don't need them in softwoods. Always use a pilot with hardwoods.

3. I too love the Robertson square screwhead. It's impossible to find deck screws in any other configuration in Canada. The Phillips star was designed to strip, after all. Developed just before WWI, it made assembly-line sheet metal installation possible. It was better to have a screw strip in an aircraft wing than to have the head shear off and have to be drilled out. Great design for purpose, but not so good for putting into wood. The Robertson head was designed for low-torque hand applications and specifically to be easily removable.
posted by bonehead at 11:48 AM on June 18, 2008

(do'h, that should be WWII)
posted by bonehead at 11:49 AM on June 18, 2008

I've never had much luck driving Phillips screws with an impact. Switch to Robertson (with a good quality bit) and you'll be happier.
posted by ssg at 1:20 PM on June 18, 2008

Just wanted to throw out there that in a drill with a clutch, if you overload the clutch setting you will smoke and burn the clutch in NO TIME. Some companies like DeWalt offer free clutch service at many of their public appearance settings...
posted by TomMelee at 7:35 PM on June 18, 2008

A handy woodworking tip is to use a bit of soft wax on the screw threads for tough to drill holes.
posted by kenliu at 9:39 PM on August 30, 2008

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