If you are one of the many people who are just discovering impact drivers, or if you’ve been using them for some time but seem to be breaking driver bits like they are made of glass, you might not be aware that traditional drill driver bits are not meant to be used with impactors.
This is due to a number of causes. The most prominent are:
- Normal bit steel isn’t rated to withstand the high torques imposed by an impact driver.
- The short impulses from the hammering action cause thousands of repeated high stress impacts every minute.
- When a fastener pulls tight, torque on the bit can quickly increase to the full strength of the driver.
If the driver bit you are using wasn’t designed for these stresses, you will end up shattering the bits. It’s as simple as that.
Impact-rated driver bits are created with high-strength steel that can withstand the stresses for much longer before they finally break down.
And yes, the impact driver bits will break, too. But you should get at least 5 to 10 times longer life than a typical hex driver bit.
Not All Impact Bits Are Made Equal
Unfortunately, you can get a cheap, so-called impact bit that will break almost as easily are a high quality non-impact bit. There are a few things to look for when trying to find a quality set of bits.
- Brand Name. Going by major brand names is a good start if you can’t remember anything else to check for. Usually the major brands do a decent job of providing good bits. DeWALT, Bosch, Milwaukee, and Snap-On, for example, usually have very good bits.
Of course most companies occasionally produce junk, too, so don’t rely on this exclusively.
- Steel Quality. This is often difficult to determine, but the steel quality is what makes the bits and sockets withstand the impacts with out breaking. You may see chrome vanadium, CRMO (chromium/molybdenum alloy, also known as chromoly steel), or even carbon steel
Carbon steel is too soft to use for impact-drivers. If you happen to see bits like this, don’t get them.
Chrome vanadium is very strong. It is commonly used in impact-ready bits and sockets. It is somewhat brittle, however, so it may not last as long as the CRMO, especially if overloaded or used in very heavy applications. However, it’s often cheaper.
Chromoly is actually chrome vanadium with molybdenum to decrease brittleness. By making it just a bit more malleable, manufacturers can more precisely machine and heat-treat the metal. Additionally, the material can absorb some impact which helps prolong tool life.
Choosing the right bits can save you lots of headaches – not to mention money – farther down the road.
Check out our accessory guide for more info on bits, sockets, adapters and more.