The gap between a drill bit announcement and the reality on a jobsite shows up fast in reviews. A 2025 launch for a new metal drilling line claimed up to 30 times longer life, savings of $230 per bit, and an end to pre-drilling, while early user reviews reported broken bits and mediocre performance. Marketing language like that makes power tool accessory selection harder, not easier, because the claims crowd out the engineering details that actually predict performance.
Drilling metal is a controlled cutting process. The bit material, point geometry, speed, and feed decide whether the hole comes out clean or the bit comes out ruined. This article covers the materials, the technique, and the way to read product claims without getting burned.
Why Metal Drilling Fails: Heat, Work Hardening, and Geometry
Metal drill bits fail for predictable reasons. Heat softens the cutting edge, work hardening turns the workpiece against the bit, and wrong geometry turns a cutting tool into a grinding tool. A bit that grinds instead of cuts makes a slow, ragged hole and dies young, which is exactly what the launch material described as normal and then promised to fix.
The fix is understanding what each material demands. Mild steel cuts easily at moderate speeds. Stainless steel work hardens fast and needs higher cobalt content, a steeper point angle, and steady feed. Hardened steel needs carbide or aggressive geometry. Other hard materials follow the same logic: masonry takes carbide-tipped bits, porcelain tile takes diamond-tipped drill bits, and steel takes ground HSS or cobalt.
The 118-degree versus 135-degree point
Point angle is the angle at the tip of the bit. A 118-degree point suits soft metals like aluminum and mild steel. A 135-degree point, usually with a split tip, suits stainless and other hard alloys because it walks less and cuts more aggressively. Using a 118-degree point on stainless invites skating, heat, and broken corners.
Work hardening in stainless steel
Stainless steel hardens at the surface as it cuts. If the bit dwells or spins without advancing, the heat hardens the work and the edge dulls against it. The cure is a sharp bit, enough downforce to keep the edge biting, and steady speed rather than timid pecking.
Run a clean sequence for every hole in metal:
- Mark the location and center punch it so the bit cannot walk.
- Start with a pilot hole at roughly one third of the final diameter.
- Step up to the final size in one or two stages.
- Apply cutting fluid or oil before and during the cut.
- Use steady pressure and a speed matched to the diameter.
- Lift the bit to clear chips on deep holes.
What the Marketing Says versus What Users Report
The launch announcement leaned on superlatives: a solution-oriented range, best-in-the-world products, up to 30 times longer life, savings up to $230 per bit, a coating that beats the heat, and a claim that pre-drilling is obsolete. The Metal Demon drill bits drew early reviews that contradict those claims, including a buyer who broke two small bits quickly and called the performance mediocre.
None of this is new ground. Spyder already sold an armored bit for tough alloys, and a center punch already solves the walking problem that pre-drilling addresses. The useful question is not whether the claims are exciting, but whether independent testing and long-term reviews back them.
Reading a tool announcement critically
Treat “up to” as a warning. A claim of 30 times longer life without published test conditions, spindle speed, material grade, or comparison baseline cannot be verified. Check the independent reviews that arrive weeks after launch, then decide.
The pre-drilling claim
Pre-drilling and center punching solve different problems. A center punch locates the hole and stops the bit from walking. A pilot hole reduces torque and guides a large bit. No bit eliminates both needs; a claim that pre-drilling is obsolete confuses the two.
| Claim | What it really means | How to verify |
|---|---|---|
| 30 times longer life | Depends entirely on test conditions | Ask for the benchmark material and speed |
| $230 savings per bit | Counts labor and replacement over bit life | Compare against a $5 cobalt bit |
| Pre-drilling obsolete | Confuses locating with piloting | Test on thick plate stock |
| One bit for all steels | Single geometry for many materials | Run the same bit in stainless and mild steel |
Bit Materials: HSS, Cobalt, Carbide, and Coatings
Bit material sets the ceiling on what a drill can cut. High-speed steel, or HSS, is the everyday choice for mild steel and softer alloys. Cobalt steel adds heat resistance for stainless. Carbide cuts the hardest materials but snaps under side load. Each step up the ladder costs more, so the right material is the cheapest one that survives the job. Metal is not the only material that punishes the wrong bit; drilling into concrete requires carbide-tipped masonry bits, and drilling into concrete follows rules of its own.
Cobalt grades explained
Cobalt steel comes in grades named for the alloy. M35 carries about 5 percent cobalt and handles stainless and tool steel. M42 carries about 8 percent and holds an edge at higher temperatures. For occasional stainless work, M35 is plenty; for production runs on hard alloys, M42 earns its price.
Coatings and their limits
Black oxide retains cutting oil and resists rust. Gold titanium nitride, or TiN, lowers friction on hard materials. Titanium aluminum nitride, or TiAlN, survives high heat. Coatings extend life, but they cannot rescue a dull edge or a wrong point angle, so treat them as a bonus, not a specification.
- HSS (M2): general-purpose, mild steel, aluminum, wood with nails.
- Cobalt M35: stainless steel, tool steel, occasional production.
- Cobalt M42: hard alloys, high heat, longer runs.
- Carbide: hardened steel, cast iron, abrasive materials; brittle under side load.
- Carbide-tipped masonry: concrete, brick, and block.
| Material | Composition | Best use | Relative cost |
|---|---|---|---|
| HSS M2 | Tungsten-molybdenum steel | Mild steel, aluminum | $ |
| Cobalt M35 | 5 percent cobalt | Stainless, tool steel | $$ |
| Cobalt M42 | 8 percent cobalt | Hard alloys, high heat | $$$ |
| Carbide | Tungsten carbide | Hardened steel, cast iron | $$$$ |
Cobalt Drill Bits for Metal: Properties and Selection
When the workpiece is stainless or hardened steel, cobalt drill bits are the standard answer. The cobalt in the alloy lets the cutting edge run hotter before softening, which matters because stainless generates heat faster than mild steel. Look for a 135-degree split point, which starts cutting on contact instead of skating across the surface.
Choose the diameter to match the fastener, then the length to match the access. Jobber-length bits cover most work. Stubby-length bits add rigidity for short, shallow holes. A 1/4-inch shank with reduced body suits drill drivers, and the size marking on the shank beats guessing from a pouch.
Stubby lengths and rigid setups
Short bits bend less, and less flex means a rounder hole and a longer-lived edge. In a drill press or a rigid handheld setup, a stubby cobalt bit drills stainless with noticeably less chatter than a long jobber bit of the same diameter.
Drill size progression
Drill the pilot at about one third of the final diameter, then open the hole in stages. Stepping in two or three increments reduces torque, keeps the cut cool, and makes the final pass clean. The practice matters more on stainless than on mild steel.
Work through the selection in order:
- Identify the workpiece grade; stainless and hardened steel call for cobalt.
- Pick M35 for occasional work and M42 for heat-heavy runs.
- Choose a 135-degree split point for hard alloys.
- Match diameter to the fastener and length to access.
- Buy two of every size you use regularly; dull bits are the real cost.
Drilling Technique That Matters More Than the Bit
Speed kills more bits than steel quality does. Spin a 1/4-inch HSS bit in mild steel at 3000 rpm and the edge overheats in seconds; the same bit at 1200 rpm with oil cuts clean. General guidance puts HSS in mild steel near 80 to 100 surface feet per minute, which works out to roughly 3000 rpm at 1/8 inch and 1200 rpm at 1/4 inch. Cobalt bits for metal construction work tolerate more heat and can run faster, but feed still matters.
Speeds and feeds basics
| Bit diameter | HSS in mild steel | Cobalt in stainless |
|---|---|---|
| 1/8 inch | 3000 rpm | 1800 rpm |
| 3/16 inch | 2000 rpm | 1200 rpm |
| 1/4 inch | 1200 rpm | 900 rpm |
| 3/8 inch | 800 rpm | 600 rpm |
| 1/2 inch | 600 rpm | 450 rpm |
These are starting points, not laws. Reduce speed when the bit smokes or the cutting edge blue-tints, increase feed until the chip comes off as a spiral rather than dust, and let the cutting fluid do its job.
Cutting fluid and cooling
Oil, paste, or spray coolant does three things: it lubricates the cutting edge, carries heat away, and flushes chips. A few drops on the pilot point before starting, then a pause to re-oil on deep holes, keeps the cut cool. Dry drilling is possible in soft metal, but it shortens bit life measurably.
- Running too fast and letting the edge overheat.
- Letting the bit dwell instead of feeding.
- Skipping the center punch and fighting a walking bit.
- Drilling stainless dry.
- Pushing a dull bit instead of replacing or resharpening it.
Building a Practical Drill Bit Kit
A useful kit organizes bits by material rather than by brand. Keep HSS for wood and mild steel, cobalt for stainless and hardened steel, carbide-tipped masonry bits for concrete, and specialty bits for tile and glass. Multi-material drill bits cover light mixed work, but dedicated bits still cut better in their own material.
Buy quality on the sizes you use most and accept economy bits for rare sizes. Replace a bit when the corners round or the cut wanders; resharpening a 1/4-inch bit is easy on a bench grinder, and a dull bit at full price cuts worse than a sharp bit at half price.
The launch lesson stands: claims about redefining a category deserve skepticism until the bits prove themselves in real hands. Pick the material for the workpiece, run the right speed, feed steadily, and the metal will cut.