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Small metal drill bits need speed, but not unlimited speed. A 1/16-inch bit in thin sheet can cut cleanly at a few thousand RPM; a 1/2-inch bit in steel needs a much slower pace. The useful rule is simple: as bit diameter increases, drilling speed must decrease. Match the drill’s gear, trigger, bit material, and cutting fluid to the hole—not just to the word “high speed” on the tool.
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What “high speed” means
Most cordless drills have a two-speed gearbox. Low gear usually provides more torque at roughly 0–500 RPM; high gear commonly runs around 0–1,800 or 0–2,000 RPM, depending on the drill. The trigger varies speed within that range. Use high gear for small bits in metal, where the bit needs more RPM and does not demand as much torque. Use low gear as the bit gets larger or the material gets tougher.
Impact drivers are a poor first choice for ordinary metal drilling. Their rapid impacts can make a bit wander, chatter, or break, and many have less controlled low-speed operation. Use a drill with a standard three-jaw chuck for better control. A basic two-speed cordless drill is usually enough for small holes in sheet metal and mild steel.
Choose speed by bit diameter
A practical starting point for high-speed-steel (HSS) bits in mild steel is about 100 surface feet per minute (SFM). That works out to roughly 6,100 RPM for a 1/16-inch bit, 3,050 RPM for a 1/8-inch bit, and 1,525 RPM for a 1/4-inch bit. Most cordless drills cannot reach the calculated speed for the very smallest bits, and that is fine. Use the fastest steady speed the drill offers, while keeping the bit cutting cleanly rather than rubbing.
For an HSS bit in tougher steel, start nearer 50–70 SFM; for aluminum, a faster cut can work, but aluminum can grab and clog the flutes. These are starting points, not guarantees. A handheld drill, blunt bit, poor support, or uncertain alloy calls for a more cautious pace. Consult the bit maker’s chart when available.
| Bit diameter | Starting drill setting in mild steel | What to watch for |
|---|---|---|
| 1/16 in. | High gear; fastest controlled trigger speed | Bit bending or snapping if it catches |
| 1/8 in. | High gear, near full speed | Heat, squealing, or a wandering start |
| 1/4 in. | High gear at reduced trigger speed, or low gear | Chatter and rising torque as the bit breaks through |
| 3/8–1/2 in. | Low gear, moderate speed | Drill twisting in your hand or bit grabbing |
The table is a field starting point, not a substitute for calculating RPM or following the bit manufacturer’s recommendations. If the drill stalls or the bit squeals without making chips, stop and reassess rather than pressing harder.
Pick a bit that suits the metal
Sharp HSS bits are inexpensive and work well for occasional holes in mild steel. Cobalt-alloy bits cost more but tolerate heat better and are useful for harder steel or repeated drilling. Titanium-coated bits are still HSS underneath; once the coating wears through, they do not become a better choice for hard metal. A cobalt bit set can be worthwhile for frequent steel work, but a sharp, ordinary HSS bit is a sensible buy for a few holes in mild steel.
For clean holes in thin sheet, a step bit can reduce grabbing and produce a round opening across several sizes. It is not ideal for deep holes or thick plate. For a single small hole, a standard sharp twist bit is usually cheaper and easier to control. Avoid using a worn bit just because it still looks intact; a dull cutting edge creates heat, rubs the metal, and often makes the job harder.
Set up and drill cleanly
Clamp the work securely. Thin sheet can spin or lift when the bit catches, so do not hold it in your hand. Mark the center with a center punch; a small dimple helps the bit start where you want it. If the hole must be accurate, begin with a small pilot hole, then enlarge it. For a hole larger than about 1/4 inch, a pilot hole can reduce the force needed, though it is not necessary for every job.
Keep the drill square to the surface and let the bit cut. Apply firm, steady pressure, not a sudden shove. Use cutting fluid on steel to reduce heat and extend bit life; a drop of suitable cutting oil is enough for a small hole. Aluminum often drills dry with a sharp bit, but a little lubricant can help prevent chips from sticking. Keep oil away from hot work and clean up spills.
When the bit is close to breaking through, ease off the pressure. Breakthrough is where the bit is most likely to grab, especially in thin sheet. If the drill has a clutch, set it to drill mode rather than a low screw-driving torque setting. Wear eye protection, remove loose clothing and jewelry, and let the bit stop before setting the drill down.
Recognize trouble before the bit fails
Blue or darkened chips, a hot bit, smoke, or a burnt smell mean too much heat. Stop, let the bit cool, add lubricant if appropriate, and reduce speed or pressure. Squealing with little or no chip formation often means the bit is dull, the speed is too low for the bit to cut cleanly, or the point is not seated. A rough, rattling hole suggests chatter; secure the work better, shorten any unsupported bit length, and use a steadier feed.
If the bit starts to bind, release the trigger. Do not twist the drill harder while it is powered. A jam can wrench your wrist, break the bit, or spin the workpiece. For larger holes, low gear gives better control and reduces the chance of a sudden catch. If your work is mostly occasional drilling into wood, plastic, and thin mild steel, a standard drill is enough. Buy a more capable drill or specialty bits only when repeated holes, harder metals, or larger diameters make the limits of your current setup clear.