Use specialty bits designed for hard surfaces (carbide, diamond, cobalt)
Select drill bits specifically engineered for the hard material you are drilling. For porcelain tile and glass, use carbide-tipped spear-point bits or diamond-coated hole saws. For stainless steel and hardened metals, use cobalt steel bits (M35 or M42 grade). For masonry, concrete, and stone, use carbide-tipped masonry bits with a hammer drill. These specialty bits are ground with tip geometries that grip hard surfaces immediately rather than skating across them.
Why It Works
Standard high-speed steel (HSS) twist bits are designed for mild steel and wood. When they contact harder materials, the cutting edges cannot bite in and the bit skates. Cobalt alloy bits maintain hardness at high temperatures generated by hard metals. Carbide tips are harder than virtually any construction material. Diamond coatings abrade through surfaces that would destroy steel edges. The correct bit for the material makes the difference between a clean start and a ruined surface.
Tips
- Tile and porcelain: Use carbide spear-point bits at 400-800 RPM with no hammer action; keep the surface wet with a sponge to cool the bit and prevent cracking
- Glass: Diamond-coated bits at very low RPM (300-500) with constant water cooling; start in a pool of water or use a ring of plumber's putty to create a water dam
- Stainless steel: Cobalt bits at 300-600 RPM with cutting oil; firm steady pressure is critical -- light pressure work-hardens stainless and makes it even harder to drill
- Concrete and masonry: Carbide-tipped masonry bits with hammer drill function engaged; let the hammer action do the work rather than pushing hard
- Specialty bits cost more ($3-8 per bit for cobalt, $8-15 for carbide spear-point, $10-25 for diamond-coated) but prevent material damage that costs far more to fix
- Common mistake: using a masonry bit on tile -- the hammer action shatters tile; switch to drill-only mode with a carbide or diamond bit for tile