How to Choose the Right Drill Bit
Choosing the correct drill bit saves time, produces cleaner holes, and prevents damage to both your workpiece and your tools. The right bit depends on three factors: the material you are drilling, the size of hole you need, and the type of fastener you plan to use. Follow these steps to select the perfect drill bit every time.
Identify the material you are drilling
Different materials require different drill bit types. Use high-speed steel (HSS) bits for wood and soft metals, cobalt bits for stainless steel and hard metals, carbide-tipped bits for masonry and concrete, and brad-point bits for clean holes in wood.
Choose the correct size for your fastener
For wood screws, the pilot hole should be slightly smaller than the screw shank. For machine screws and bolts, use a tap drill chart to find the exact size needed for threading. When in doubt, start with a smaller bit and work up.
Consider the depth of the hole
Mark the desired depth on your drill bit with masking tape to ensure consistent depth. For through-holes, place scrap material behind your workpiece to prevent tearout. For blind holes, stop short of full depth and clean out chips.
Use the correct speed and pressure
Larger drill bits require slower speeds to prevent overheating. As a general rule, reduce RPM as bit diameter increases. Use steady, moderate pressure and let the bit do the cutting. Excessive force causes overheating and premature dulling.
Start with a pilot hole for large bits
For drill bits larger than 1/4 inch, start with a smaller pilot hole to guide the larger bit. This prevents the bit from wandering, reduces the force needed, and produces a cleaner hole. A 1/8-inch pilot hole works well for most situations.
Drill Bit Types
Twist Bits (HSS)
The most versatile drill bit type. High-speed steel twist bits work in wood, plastic, and soft metals. They are inexpensive and available in every size. The helical flutes carry chips out of the hole as you drill.
Cobalt Bits
Made from an alloy of cobalt and high-speed steel, these bits resist heat better than standard HSS. Use them for stainless steel, cast iron, titanium, and other hard metals. They cost more but last significantly longer in demanding materials.
Brad-Point Bits
Designed specifically for wood, brad-point bits have a sharp center point and angled spurs that score the wood fibers before cutting. This produces clean, precise holes with no tearout. Ideal for doweling, furniture making, and any application where hole quality matters.
Masonry Bits
Carbide-tipped masonry bits are designed for concrete, brick, block, and stone. They feature a wider carbide tip that pulverizes the material as the bit rotates. Use with a hammer drill for best results in concrete. Standard rotation mode works for softer masonry like brick.
Frequently Asked Questions
What drill bit should I use for metal?
For mild steel and aluminum, use high-speed steel (HSS) bits. For stainless steel and hardened metals, use cobalt bits (M35 or M42). Run the drill at a slower speed and use cutting oil to reduce heat buildup and extend bit life.
Can I use a wood drill bit on metal?
No. Wood bits like brad-point and spade bits are not designed for metal and will dull quickly or break. Use HSS or cobalt twist bits for metal. Conversely, standard twist bits work on both wood and metal, though brad-point bits give cleaner holes in wood.
How do I prevent my drill bit from wandering?
Use a center punch to create a small dimple at the drilling point before starting. This gives the bit tip a place to sit and prevents it from skating across the surface. For metal, this step is especially important.
When should I use a step drill bit?
Step drill bits (also called unibit or cone bits) are ideal for drilling holes in thin sheet metal, electrical boxes, and panels. They can cut multiple hole sizes with a single bit and leave clean, burr-free edges.
How often should I sharpen my drill bits?
Sharpen drill bits when they start producing chips instead of curls, require excessive pressure, or generate excessive heat. A bench grinder with a drill bit sharpening jig works well for HSS bits. Cobalt and carbide bits require specialized sharpening equipment.