How to avoid stripping screw heads?

Question

In at least two different contexts now (installing shower handrails, installing gate on fence) I've found myself stripping the head of the screw beyond all use. I must be doing something wrong, so what is it?

The screws I'm driving are two or three inches long with a Phillips head. I'm using a cordless drill with a Phillips bit. I find that no matter how hard I push from behind the drill (even with all the body weight I can muster) and no matter what speed I drive at, the drill bit jumps out of the head of the screw. When that happens repeatedly (either because I think I can make it if I just push it harder, or I get frustrated), the head ends up getting stripped and then I've got multiple problems (getting the screw out, replacing it, and getting the replacement in without stripping it) that set the project back. What am I doing wrong?

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UPDATE: Thanks to all who contributed to the great answers below! After checking my screws and bits (Phillips, not Pozidriv; right size, not worn), drilling wider pilot holes and then being careful with the speed and torque, I decided I wasn't using the right tool for the job (what's that they say about bad workmen?) and I went and got an impact driver. Then the first few screws went in like magic --- it was incredible! And then it sheared off the heads of the next couple of screws. Grrr! I couldn't manage to get the remnants out, and ended up drilling new holes in which I tried some new store-bought screws --- same result. Double grrr! So I drilled some new holes and tried some hex-head screws, which went in just fine with a socket on my cordless drill. Hurray!

Conclusion: I hate Phillips heads for high-torque situations; I much prefer hex heads. That's how I settled this particular matter, but there are some very important and useful answers below that were not "accepted" that nevertheless may help people in slightly different circumstances.

Answer 1

What am I doing wrong?

If you're stripping the heads, Phillips head screws probably aren't the right kind for the job. They cam out under excessive torque ^[1]. And once they do, the bit becomes a grinding tool, chipping away the head. They're good for uses where high torque isn't required. Phillips head screws intended for use where they might require some torque are hardened, which reduces the chipping if they cam out.

The solution is to use the right kind of screw for the job, and to not substitute brute force for proper technique in a demanding situation. Excessive torque shouldn't be required if you don't cut corners on technique. But if a lot of torque is needed, use screws that can handle it.

• Drill a pilot hole. There are actually different optimum-sized pilot holes recommended for different materials. With soft wood, a precisely sized pilot hole often isn't critical if you are close, but If you are screwing into hardwood or metal, the right size pilot hole is important.
• Lubricate the threads by rubbing the screw on some candle wax or bar soap (not liquid soap), before you drive it.
• Don't use a worn driver bit or one that is not the exact size for the head. This is especially important for Phillips head bits because camming out and grinding away the head also grinds away the bit, making it more prone to cam out.
• In a demanding situation, use hardened screws or a different type of head. For example, square, hex (Allen), or star (Torx) socket heads are common for high-torque applications, or a hex head that you use a socket to turn.

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^[1] _{There's a long-running argument on whether cam out was an intentional design objective or just a characteristic of the design. According to Wikipedia: The design is often criticized for its tendency to cam out at lower torque levels than other "cross head" designs. There has long been a popular belief that this was actually a deliberate feature of the design, for the purpose of assembling aluminum aircraft without overtightening the fasteners. Extensive evidence is lacking for this specific narrative, and the feature is not mentioned in the original patents. However, a 1949 refinement to the original design described in US Patent #2,474,994 describes this feature.}

Answer 2

You may be having one or more of the problems as follows:

1. You are using the wrong size driver bit for the screw type. Make sure the bit fits perfectly in the slot of the screw.
2. You may be trying to use a driver bit that has its edges rounded off so bad from previous usage that the bit is next to useless.
3. You may have a really cheap driver bit chosen from a large assortment set. Very often these cheap sets have driver bits that are made of very soft metal and easily strip.
4. You may not be drilling a proper sized pilot hole for the screw. The pilot hole needs to match the inside diameter of the screw thread so that there is a place for the body of the screw to enter the hole and just allow the screw threads to engage the inside surface of the pilot hole.
5. You may be using screws of a type incompatible with the materials that you are attempting to screw into. There are specific type screws for wood, sheet steel and aluminum.
6. You may be neglecting to lubricate the screw before attempting to drive it home. Rubbing the screw threads across a soft bar of bath soap can make all the difference in getting a screw installed. Liquid soap is not generally recommended as it can stain the wood if it runs out on the wood surface.
7. If you are screwing into a metal piece there is a decided limit of the thickness that a given screw can penetrate even with proper pilot hole and material compatible screws.

Answer 3

What am I doing wrong?

Using a drill to drive screws. I used to have the same problem as you, until I switched to using an Impact driver instead.

Drills are designed for drilling holes. They deliver a nice consistent torque. When the resistance of the screw increases this tends to cause camming out.

Impact drivers are designed for driving screws. They deliver a variable torque. When the resistance of the screw increases the variable torque "kicks" the screw round, making camming out less likely. (Not sure I've got the physics of "why" they work better quite right. But I promise you they do.)

Answer 4

It could be that the driver you are using is not a Phillips but a Pozidriv or the screws are Pozidriv and the driver is a Phillips.

See https://www.finehomebuilding.com/2015/09/16/what-is-the-difference-screw-bits-phillips-vs-pozidriv

Answer 5

A common mistake of inexperienced people is going straight in with a fancy power tool, and never learning the task with hand tools. This deprives you of a lot of tactile-experience knowledge that is essential to success.

If you had used a plain old Philips screwdriver, first you wouldn't chew up the heads. Second, you would quickly discover the core problem: you are asking the screw to perform way beyond its design ability. The material you're screwing into is too hard, or you're drilling too deep, etc. You would take a hard look at the material and pre-drill the hole, and if that is not enough, pre-drill it somewhat larger -- until it is possible to drive the screw with a common screwdriver.

After the first one, you now know which drill size is correct for pre-drilling. So you simply leave that drill in the drill/driver.

What about doing many of them? I grab my speed wrench and bit holder.

image source

This give me several things at the same time:

• speed of work about that of a power tool (I've done a roof with this)
• precise control not possible with power tools - I set exactly the depth I want
• no rat-tat-tat camming out the Philips head, when it jumps, just stop
• extremely accurate torque feedback, so no chance of breaking a screw off
• the ability to push Quite Hard on the screw head
• never runs out of batteries

Answer 6

You mentioned you're using a cordless drill. Remember that there's a difference between drilling (torque goes to bit speed) and driving (torque goes to power behind the screwing). If you ever buy a cordless screwdriver, it only does driving.

If you have a more recent model cordless drill, it may have a switch between the two (my Dewalt does) and you'll note the difference immediately, because in driving mode the bit doesn't spin anywhere near as fast.

Impact drivers add vibration to the driving mix. They drive until the bit encounters resistance and then it vibrates the bit to help drive the screw (it makes a loud racket in the process). Do NOT confuse these with hammer drills, as hammer drills are meant to pound drill bits through masonry. Also, be sure any screwdriver bits you use with an impact driver are meant for that purpose (they can shred regular drill bits that aren't hardened against the vibration).

Answer 7

I was having this same problem with small electronics. I am actually very surprised that I haven't seen anyone mention JIS (Japanese Industrial Standard) screwdrivers yet.

IIRC, Phillips head screws are actually specifically designed to cam out at a certain torque. This is due to the design of the head of the screw/screwdriver. Basically, the JIS is straighter so rather than cam out, it grabs.

Here is a good video demonstrating the difference between JIS and Phillips: https://www.youtube.com/watch?v=gEwVUZr5xxQ

The beauty of the JIS screwdriver is that it fits the Phillips screw so you can pick up a whole set of JIS screwdrivers and they are still universally usable.

Given how useful they are, it honestly amazes me that they are rarely found outside of Japan. (I actually had to order mine from Japan)

Answer 8

Lots of feedback here, but I want to stress a point that others have mentioned in passing:

Star Drive, AKA "Torx"

I almost exclusively use "star drive" (AKA torx) "construction screws" such as these Grip-Rite construction screws or if you want, pan-head ones from Spax.

Impact Driver ≠ Drill

Also I've found an impact driver is much more effective. I own the Dewalt brushless model which I use for most "screwing" jobs. (If you already own other cordless tools like Milwaukee, Makita, etc. I'm sure the impact driver for any of them is decent.)

If I need, I can drive a 6" lag bolt through hard wood without pilot drilling. YMMV, unless you're doing rough work it's still a good idea to drill pilots so you don't crack the wood! But the issue is no longer stripping the screw head. I've literally snapped screws if I'm being careless and drive into something too hard, but I no longer worry about ever stripping a screw head.

Construction screws FTW!

Answer 9

Totally agree with others here that hex, Torx, Pozidriv, etc are all better for most purposes since Philips are explicitly designed to cam out, which was needed for older automated assembly equipment that relied on that to stop from overdriving the screw, rather than just measuring torque and stopping on its own like any modern robot would.

I wanted to add one more thing for people to keep in mind for the situations when you only have the inferior Philips screws and a regular drill available though.

Many drills have a variable torque clutch thing (usually a ring around the chuck area that you can rotate). In general, try to start with this on the low end of the range and try driving in the screw. If it ratchets before you're done, you'll know you need more torque and can turn the torque up AND use more pressure to avoid camming out and stripping your head and bit all to pieces. The idea is to keep that clutch low enough so that you can't apply more torque than the screw can handle. If you need more torque, the drill will ratchet harmlessly instead of stripping your screw. When it happens, then I usually reposition myself to apply more force and then turn the torque up. The other nice thing about this is if you're driving say 10 screws into something, you can adjust the torque on the first one or two so that it ratchets right as you want it to stop, then you know you can drive the other 8 with just the right amount of torque to tighten it without overdriving it and potentially damaging your material, breaking off a head, etc.

Answer 10

I try to use robertson (square) for most applications. With those, stripping the head is usually a case of using an incorrect bit size for the screw.

Answer 11

I've been doing a lot of work over the last 3 years with high torque screws. The work has involved formwork for concrete, so it's got to be very strongly built and solid - everything is 2x4 inch (47x100mm) timber, sometimes 3x6 inch (75x100 mm). The screws have been ordinary wood screws but also 6 inch (150mm) heavy duty timber screws. I use a drill/drill driver rather than an impact driver, which has separate speed and torque control.

What I've found is a mix of things, maybe some of them will help:

• Screw head - the screw head is crucial. Ordinary crosshead (Phillips) cam out or deform too easily. Pozidrive are good. But for pozidrive, the crucial thing is you need a bit+screw that's a tight fit, to make them work. A pozidrive that's a loose fit will have the same problems as ordinary phillips. Good brand removable pozidrive bits ("hex" style shank) are cheap - use those and buy a good brand. Beyond pozidrive, screws with hex and torx heads are ideal - they've never cammed out for me and are designed for high torque. But not all screws and sizes have them. They are also often more expensive, so you may wish to find ways to avoid them and get "ordinary" heads to work for you. The screws I use most are pozidrive (up to about 100mm) and hex/torx heavy duty heads (around 250+ mm).
• Screw quality - I've noticed that some cheaper screws seem to be much softer, or the slots in the head are softer - they deform much more easily than other similar screws of other cheap brands. Try a couple of different screws of the same nominal size, and see if some of them go in and out multiple times , while others start to become deformed after just going in once, with tough wood/materials. I've had this even with big screws going into plastic plugs in concrete - there's one brand that just seems to have soft heads that never keep their slots, that I just don't use any more.
• Speed control - going too fast means that when a camout happens, the bit will keep hammering the slots as it cams, and this harms both. Aim for slow/variable speed, high torque - and enough pressure to keep the bit held tightly in the slot. But aim for slow speed/high torque. Having a drill/driver with these as separate controls has been crucial. Often, going slow also means less torque - which is a problem.

Answer 12

You guys in the US need to find a way to import Robertson screws. They are by far the best screws high torque applications. The history goes like this

Robertson screw company was in a deal with Henry Ford himself. Ford wanted exclusivity for Robertson head screws for the Ford Motor Company. Robertson declined to grant exclusivity and Ford basically ran the Milton Ontario headquartered company out of the States. Now American products and all the American imports to Canada have those darn philips screws or hex screws. They just aren't very good for high torque applications. And the bits wear out extremely quickly.

Answer 13

Rounding off Phillips head screws is something we have all experienced.

When unscrewing Phillip head screws that I know are not tight (from experience), I use a battery operated screwdriver. If they are tight, I try using a regular Phillips head screwdriver with the size (#1, #2, or #3) to match the screw. And, if it loosens, I then use that screwdriver, the battery operated one, or a drill, depending on how many screws there are to remove. Occasionally though the screwdriver will not turn the screw. Then I use an impact driver which you hit with a hammer. That always gets the really hard ones out.

Answer 14

There's been one mention of torque so far, but that answer didn't mention that you can often vary the maximum torque with a clutch. My 18V cordless (an older version of this one) has a collar to set the torque in steps up to 22, then drill, then hammer drill. Torque up to about 10 is good for most woodscrews, except small ones that I'd do by hand anyway. Torque 15 or more often snaps screws if they're not a type that can cam out but is good for coach screws.

Speed control is done with the trigger (actually mine has 2 ranges with a switch as well) and there's no need to go flat out when screwing, except in the middle of a really long screw - start slow and finish slow.