Practical Metal Drill Bits Worth Buying
Quick Answer
Metal drill bits are defined mainly by their material and coating, not just size — the right bit choice depends on what metal is actually being drilled, since a bit suited to soft aluminum will dull quickly or overheat in hardened steel.
Bit Materials
- High-speed steel (HSS): the standard, affordable choice for general metal drilling in mild steel and aluminum.
- Cobalt (M35/M42): retains hardness at higher temperatures, better suited to stainless steel and harder alloys that generate more heat during drilling.
- Titanium-coated HSS: a thin titanium nitride coating reduces friction and extends bit life over uncoated HSS, though the coating wears away with repeated sharpening.
Why Speed and Pressure Matter
Metal drilling generates significant heat from friction — running the drill too fast for the bit and material overheats and dulls the cutting edge quickly. Slower speeds with steady, moderate pressure and cutting fluid (for harder metals) extend bit life considerably more than raw drilling speed.
Starting the Hole Accurately
A center punch mark prevents the bit from wandering across a smooth metal surface before it bites in — attempting to drill directly on flat, hard metal without a starter mark is a common cause of an off-target hole.
Point Angle
Standard bits have a 118-degree point angle suited to general-purpose drilling; a 135-degree split-point angle self-centers better and reduces walking on hard, smooth surfaces, an advantage on stainless steel specifically.
Bottom Line
Cobalt bits earn their higher price on stainless steel and hard alloys, while standard HSS handles mild steel and aluminum reliably — a center punch mark and appropriate speed for the material matter as much as bit quality for a clean, accurate hole.
