The Home Machinist

The tale of the recalcitrant screw.

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The silence of the shop hangs like a pregnant pause these many months, cobwebs gathering in the twilight. The lathe chuck quietly assumes an orange patina of rust as jewel-like beetles scuttle about, dodging the dust motes caught in the pale eye of a winter sun. OK, thats over the top, but you get the idea. Its been awhile since Ive been out there.

Look familiar?

But a little something Ive been working on for some time is the problem of dealing with the fouled-up screw head. That is, the head is stripped, so now what? Inspiration came from Henry James The Turn of the Screw written in 1898. He described his horror story as the strange and sinister embroidered on the very type of the normal and easy. It seems a fitting description of this too frequently encountered situation.

A search through the tool box and several passes at the tooling suppliers turned up an interesting group of solutions, some surprises as to whats hard to find and a couple of new entries in the race for your money.

A fairly new bit on the left, but one you probably have in your tool box on the right. Throw the damaged one away now!

Cause and Effect

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First, lets look at the cause before we investigate the cure. Regular readers will remember an earlier column describing the Phillips head screw-form as being a curse in the guise of a gift. Granted, it beats a straight-slot screw and does keep the tool off the surrounding area-assuming it doesn’t slip.

There’s the rub. It can slip because it was designed to force the tool out of engagement to prevent over-torquing of the screw. So in our wisdom, we simply lean against the tool until the screw is tight. Then, to extract the screw we have to lean in even more with the inevitable hurling of the tool as far as we can when it skitters off through the new paint.

When you retrieve the driver from your neighbors yard, get out a jewelers loupe and take a close look at the condition of that cruciform tip; even with the most expensive screwdrivers, its a mess after just a few years use. It was designed to cam-out and now it really has no grip, because those square edges look like a WW-I minefield.

Top row? All #2. Bottom row? #1ish. But look closely, and you’ll see that no two are really alike.

Use either replaceable bits and replace them frequently, or buy Craftsman screwdrivers. I take advantage of Sears lifetime replacement policy-I haul a bag back every couple of years and simply pick out new ones. There’s no paperwork either green or duplicate; you just go one-for-one and have fun.

The EZ-Out brand of broken bolt extractor. Drill a hole in the bolt, tap this into the hole, and press down while turning counter-clockwise with a small wrench.

Quick and Cheap

But what if you’re stuck? Its late at night, the hardware store is closed, and that screw has got to go. The answer is EZ Grip Friction Drops. Its a black, gooey liquid with microscopic diamonds in suspension. A tiny drop of it into the head of the screw and all the sharp corners of those diamonds bite into the screw/driver interface. Turn, and out comes the offending screw. A tiny tube of this wonder goop has lasted several years in my hands. Youll find it with a search of eBay for about $12.

If you’ve totally rounded the screw with an electric screwdriver (you didn’t do that, of course) you might resort to the tried and true EZ-Out. Drill a deep hole into the screw, select the right size EZ-Out, tap it into position, apply a properly sized adjustable open-end wrench (aka Crescent wrench), push on the EZ-Out while rotating, and out comes the screw…most of the time. Its a bit laborious, but it has a long history of success. Most any tool shop will have a set of four for $25 to $35.

This impact driver is from Snap-On. Its effective if the surrounding material can withstand aggressive hammering.

A solution of about the same vintage is the handheld impact driver. Mine was purchased almost 30 years ago off the Snap-On truck and has never failed. It does require extra-strong tips mounted in 3⁄8-inch square drives and a 16-ounce hammer. Place the bit on the handle, and insert it into the screw. Twist the handle and it rotates about one-eighth of a turn. Hold that position, and smack the end of the tool with the hammer. The blow pushes the tip into the screw while engaging a spiral within the handle. The problem screw is a problem no more.

The limit, however, is that the surrounding material has to be able to withstand a really hard whack with a substantial hammer. This was fine on a motorcycle engine, but not on an aircraft wing, and certainly not if a ball or roller bearing is involved.

New and Improved

In an age of 20 ways to make a phone call, there are bound to be new ways of removing screws. Enter the Grabit, a tool that sounds more like a Lewis Carroll monster of the id than an efficient tool for dealing with fouled Phillips heads. The operation is akin to the EZ-Out in that it is a drill and counter-clockwise spiral. The advantages here, though, are several: no guessing what drill to use with which EZ-Out; the drill is one end of the tool and the reversing portion is on the other; you use only an electric/reversible drill motor, and there’s no separate drill bit, wrench or hammer to tap in the tool. Just drill a smooth, properly shaped cavity, flip the tool around, push, and with the motor still in reverse, out comes the screw.

Left: Alden Pro Grabit is available at Sears or Orchard Supply. No moving parts, but you do have to flip the extractor over. Right: The drill-out power extractor from Craftsman. No flipping the tool as with the Grabit type of extractor, but its a bit more complex, so durability can be assessed only with extended use.

The greatest advantage over the EZ-Out is that the depth of the material removed is shallow, hence the diminished potential for hitting the threads of the base material when you don’t get the drilled hole exactly on-center.

Go to the company’s web site at www.4grabit.com to buy one or see a video of it in use. Warning about the video: Turn down the sound and be prepared for a ShamWow/Vince presentation.

Going one step further is the drill-out power extractor from Craftsman. Its operation is similar to the Grabit, but there is no need to reverse the tool. The drill is a left-handed cutter with the extractor section just above it. Put the drill motor in reverse and start cutting; eventually the extractor will engage the hole you’ve formed, take the load off the cutting end and extract the screw. Should the extractor not have sufficient grip, the cutter simply deepens the hole until the tapered extractor properly engages.

Ill confuse and simplify this at the same time by pointing out that the four-piece Grabit set and the three-piece Craftsman set are, you guessed it, available as a seven-piece set for about $40 from Amazon.com under Drill Out Power Extractor Kit (7017P).

The reason to purchase all seven is simple enough. Screws come in a wide range of sizes, and this one kit will handle it all for about the same price as the four-piece EZ-Out set. The larger three will handle screw removal when the head is fouled but drillable; the smaller four will even take on a twisted-off screw with no head at all. Lest you think Ill never need all these, consider that the price of the kit through Amazon is about the price of each set when purchased separately.

Tapped Out

If you’ve really had a bad mojo laid on you and you broke a tap, forget all those other solutions for one unavoidable reason: Taps are harder than drill bits.

Broken tap? Forget all the other solutions. These come in two-, three- and four-flute versions. Clean out the debris, slide the fingers down between the flutes of the tap; slide the long collar down to minimize the bending moment on the fingers; gently wiggle and turn the square top to get the tap out. Easier done than said.

To extract a broken tap, start by putting away the hammer and prick punch for the same reason as you put away the drill bits. The hardness that allows you to cut threads means the tap is also brittle. This means that if you start by tapping, tapping, tapping in an attempt to rotate the piece still in the hole, you’re likely to shatter it into smaller bits without removing the major portion.

Sit quietly and contemplate the nature of the task. To start the tap you have to push in a bit while rotating the handle. After a thread or two is cut the only force needed is rotational. But the practice of unsupported hand-tapping is prone to pushing on one side of the tap handle more than the other, especially as the tap size enlarges. The result is a demonstration of non-plastic deformation and exhibition of the cleavage planes characteristic of brittle fracture-and a few unprintable words.

The good news is that the tap was most likely broken because a force was applied perpendicular to the axis of rotation. This means that the threaded portion is not the cause of the breakage, and the junk isn’t really hard to remove if you could just push in the right way.

Once you’ve recovered your inner Buddha and decided to salvage the situation, the outlook is not so bleak. Step one is to extract all of the loose parts. Chances are that when the tap shattered it did just as would any other brittle material. It came apart in many pieces, and a lot of them are down the hole. Wear your safety glasses, throw a towel over the whole, and blow out what you can. Now pick out the rest with a dental pick. Don’t try to rotate the tap, as it might be broken with major pieces in place, and the pieces will simply jam against one another.

The tool to use (you knew I had one) is a tap extractor. Taps have flutes, so there will be some place for the chips to go, and it is these flutes that will allow you to turn the tap backward. The tap extractors fingers are inserted into the flutes, and the stabilizing collar is brought down to support the finger. Turning the extractor in reverse will then apply a force to all the loose parts exactly where it needs to be, down in the cutting area and to all the cutting surfaces simultaneously.

They work very well, but the drawback is the expense. A typical home collection of 20 taps has two-, three- and maybe a couple of four-flute taps. To cover the entire range you need perhaps a half dozen extractors with two, three and four fingers in various sizes at about $20 each.

Worse, you will not find these at the local hardware store or even the big box stores such as Home Depot. A tour of the tool-only shops generated the same blank look from the clerk: Never heard of it. If you have a shop that supplies to the local machine shops you might have better luck, but no guarantee. You will, however, find them by calling Dan-Mar Tool & Supply in San Carlos, California (650/591-2651). While expensive, they could be a lot cheaper than having to replace the component.

Editors note: If you have specific questions for author Bob Fritz, or if you have certain projects youd like us to cover, email us at editorial@kitplanes.com with Home Machinist in the subject line.

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