We’ll be the first to admit using a drill bit designed for wood to drill holes in steel or aluminum. The results were predicable–billows of smoke and holes that were anything but round. Chances are better than even you’ve done the same. No worries, we’re all friends here.
It can be hard to tell the difference between the two types. At first glance, drill bits all look pretty much the same in term of size and shape. Many are the same color. To make matters more confusing, many drill bits are multi-purpose, meaning they can be used on a variety of materials.
Fortunately, there are ways to tell the difference between drill bits for wood and those for metal. Most (and we underscore ‘most’) metal bits can be identified by their black oxide or gold titanium nitride finish. The hard titanium nitride coating greatly extends bit life.
Wood bits can usually be identified by their silver color. Most have a sharp projection on the end called a brad (or spar). It’s there to keep the bit centered and prevent it from wandering when drilling. There is often a lip around the end of the bit too. Its purpose is to slice through the wood fibers to keep the hole as round as possible.
Some wood bits do not have a brad on the tip, and that’s where the trouble can begin. Wood-only bits have a slower cutting speed to prevent splitting or splintering of the material. That’s why you’ll see smoke when using a wood bit to slice (or more correctly, burn) a hole through steel. You need a high-speed bit to make nice clean holes in metal.
When drilling metal, don’t crank the drill up to wide open throttle. Slow down and let the drill do the work. Use cutting fluid if you can. It reduces the friction between the drill bit and the material you’re working on. It also helps to dissipate heat and makes it easier pick up and remove chips. Light weight engine oil (SAE 20, for example) or lightweight machine oil will work in a pinch.
These drill bits are all the same size (5/16-inch) but are designed for use on different materials. Even the steel they’re made from is different. Inexpensive drill bits are manufactured from carbon steel. Better drill bits, particularly those designed for metal, are made from an alloy steel. (Image/Wayne Scraba)This is a drill bit for wood. Note the brad in the center and the lip partially surrounding the circumference. The brad is designed to center the bit in the wood while the lip helps to cleanly slice through the wood fibers. (Image/Wayne Scraba)This is a titanium nitride-coated high speed drill bit. The coating hardens the bit and can extend the life by a considerable margin—between three and six times according to the manufacturers. (Image/Wayne Scraba)Other high-speed bits have a black oxide coating like this one does. In general, high-speed bits for metal shouldn’t be used on wood because they tend to split or splinter the material. (Image/Wayne Scraba)Most bits for wood are silver in color and aren’t good for drilling in metal. This drill bit set is an exception to that “rule.” As the instruction sheet says, these bits can be used for most metals and some types of wood, mostly harder species like oak. (Image/Wayne Scraba)Step drill bits like these Summit Racing™ Step-Drill Bits use a stepped, single cutting-edge design to penetrate sheet metal, plastic, and fiberglass up to 1/8-inch thick better than traditional twist-type drill bits. These bits eliminate the need for center punch holes and automatically deburr the hole as it’s drilled. The set includes one six-step bit (3/16- to 1/2-inch), one nine-step bit (1/4-to 3/4-inch), and one 13-step bit (1/8- to 1/2-inch). (Image/Summit Racing)This is a masonry bit. Don’t bother using it on metal—you’ll just make lots of scratches and gouges. Bits for concrete are similar. They don’t work on metal either. (Image/Wayne Scraba)Another bit that won’t work on metal is this hammer drill bit. It’s designed for use with hammer drills where the rotary action of the drill is coupled with the hammer action of the tool to punch through material. They’re most often used for concrete or stone. (Image/Wayne Scraba)This special drill bit is designed to go through granite tile. I used it to drill a hole in hardened steel and it worked where none of the others managed to make more than a scratch. You can see it got hot during operation. (Image/Wayne Scraba)Cutting fluid like this Evolution Cutting Fluid available at Summit Racing reduces the friction between the drill bit and the material you’re working on. It also helps to dissipate heat and makes it easier pick up and remove chips. (Image/Summit Racing)
Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.
Comments
One response to “Drill, Baby, Drill: The Differences Between Metal and Wood Drill Bits”
thanks Wayne. very informative.