How Impact Drivers Work

[Tom Walz]

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This is a Wiha Terminator Impact Bit designed for use in impact drivers.It is rated to give up to 30 times the performance of standard bits.

When Wiha came out with these,we bought a couple of sets and gave them away to some of our testers to use inreal-world applications. They worked really well so we started selling them.

There was a post here about these so I decided to provide an overview of how they work.
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The first thing I tried was a pocketknife to remove the plastic sleeve.The pocketknife scraped the sleeve a little bit but certainly did not cut it.

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The next thing I tried was a Dremel tool with a cutting disk in it. Last time I used this disk was to cut through a 3/8 inch stainless steel bolt.

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The Dremel disk cut through the plastic and revealed that the magic in impact bits is a thinner waist of an extremely sophisticated metal.

The metal is CVM (Chromium – Molybdenum – Vanadium steel)
AMSnumber 6304
C (Carbon)0.40 – 0.50Mn (Manganese) 0.40 – 0.70Si (Silicon) 0.15 – 0.35Cr (Chrome) 0.80 – 1.10Ni (Nickel) 0.25 maxMo (Molybdenum) 0.45 - 0 .65
V (Vanadium) 0.25 – 0.35
Totalapp 3%

First, this is clearly a forged bit so the chemistry of the metal is identical throughout the whole bit. The bit is rigid enough to drive screws or bolts rapidly and well. However, when the bit encounters excessive force the narrower, plastic encased center absorbs the force and spreads it out through a torque like affect somewhat similar to the way McPherson strut suspensions work on race cars.

Essentially, when the tool is thick enough it is rigid up to a certain force.When that force is exceeded, the thinner metal part slowly wants to twist and the more force that is applied the more resistance the inner part offers.

Somewhere in Wiha, there is one or more metallurgists who are incredibly good. Developing a metal will do this is an extremely good trick. Developing a metal that will do this millions of times reliably from a mass production environment is truly impressive.

The secret to that is selective heat treating. The whole part is heat treated to make it case hardened so that it has a wear resistant outershell over an impact resistant core. Then the narrower center of the bit is once again heat treated and tempered to make it much tougher. So you have hard, wear resistant steel at the wear points top and bottom. And you have a softer, tougher impact resistant center.

[ray hampton]

I have not try your impact driver but the impact driver will remove most screws, I made one from a screw-driver shank and a steel handle

[Ole Anderson]

I have some DeWalt bits that are ground down to a smaller diameter mid shaft, I presume to limit torque transmitted, like torque limiting wheel nut impact drivers you see at a tire shop. Not unusual to break standard bits with an impact driver, done it many times. And why would you make a bit from a screwdriver when you can buy them for a quarter? Just because you can is an acceptable answer, but doesn't make much sense.

[Art Mann]

I don't have a very high failure rate using the inexpensive bits you can buy at big box stores. I have built a lot of decks with them. I lose them long before they are warn out or break.

[Larry Frank]

These are interesting bits and I went to the website and watched the videos. However, at around $4 per impact bit, they are a bit pricey. I suppose in an industrial application, these might be a good investment. I wonder what type of fasteners that you could ever use that would push these impact bits to actual failure and make them an economical choice.

I have driven hundreds of deck screws with an impact driver and cheap bits and not had a failure due to breakage. More often, I break the screw even good deck screws.