Cobalt drill bits sit at the top of the twist drill lineup for metal work, and a recent packaging battle between two major power tool brands put them back in the spotlight. One brand now prints “up to 2x longer life” versus its chief rival directly on the box of its Elite cobalt sets, which makes this a good moment to separate marketing from metallurgy. The properties, selection criteria, and drilling techniques that govern cobalt drill bits for metal drilling determine whether that promise holds up on a real jobsite, and the alloy chemistry explains most of the price difference between a budget set and a premium one.
This article covers what cobalt actually adds to a cutting edge, how to read lifespan claims printed on retail packaging, how to match bit geometry and shank style to the drill that drives them, and a step-by-step routine for drilling stainless steel and other hard metals. It also walks through the speeds and voltages that matter and the maintenance habits that keep a bit set productive for years.
What Cobalt Drill Bits Do Differently
Choosing the right cobalt drill bits for metal construction starts with understanding what the alloy does inside the cutting edge. Standard high speed steel (HSS) bits blend iron, carbon, chromium, vanadium, and tungsten. Cobalt bits replace part of that recipe with cobalt, typically 5 percent in M35 grade or 8 percent in M42 grade, and that single change shifts how the edge behaves when it gets hot.
Red hardness: the property that matters
Steel cutting edges soften as they heat up. HSS begins to lose hardness around 500 F (260 C), which is why a standard bit dulls fast in stainless steel. Cobalt raises the temperature at which the edge softens, a property metallurgists call red hardness, because the edge stays hard even when it starts to glow. That is the entire reason cobalt bits cost more and last longer in hard metals.
M35 versus M42 grades
M35 carries about 5 percent cobalt and resists chipping, which makes it a solid all-around choice for general metal work. M42 carries about 8 percent cobalt, tolerates more heat, and holds an edge longer in abrasive materials such as stainless steel and titanium. The tradeoff is toughness; higher cobalt content produces a slightly more brittle edge that demands steady drilling technique.
| Property | HSS | Cobalt (M35/M42) | Carbide |
|---|---|---|---|
| Edge temperature limit | ~500 F | ~1,100 F | ~1,800 F |
| Hardness at high heat | Low | High | Highest |
| Toughness | High | Medium | Low (brittle) |
| Typical cost for a 1/4 in bit | $3-6 | $8-15 | $15-40 |
| Best use | Wood and mild steel | Stainless and hard steel | Production drilling and composites |
For plumbers, metal fabricators, and framing crews that drill into steel regularly, the middle column is usually the right answer. Carbide earns its price only in high volume production or on materials that destroy HSS edges in minutes.
How to Read Drill Bit Marketing Claims
Independent coverage of the Elite series accessories shows a pattern worth studying. The claim that a bit set lasts “up to 2x longer” than a competitor appears on packaging, in ads, and in press materials, but the fine print defines the test: low carbon steel at 1/8 inch thick, drilled at 1,200 RPM, and only for specific bit sizes. Change the material to stainless or the thickness to 1/4 inch and the claim no longer applies.
What “up to” really means
Retailers lean on the phrase because it is nearly impossible to disprove. “Save up to 40 percent” can be true when one item in the store carries a 40 percent markdown while everything else drops 5 percent. A lifespan claim of “up to 2x” works the same way; a single favorable test condition makes the statement technically accurate.
A practical checklist for reading any drill bit claim:
- Find the fine print and note the exact material, thickness, and speed tested.
- Ask whether the test matches the drilling you actually do.
- Compare against the competitor’s published specs, not the headline.
- Check the full product line, because claims often cover only a handful of sizes.
- Fold the warranty and return policy into the value math.
Selecting the Right Drill Bit for the Job
The same power tool accessory selection logic that applies to drill bits, driver bits, and spade bits applies here: match the geometry to the material and to the tool that spins it. A cobalt bit with a pilot point tip eliminates the need for a separate pilot hole in sizes over 5/16 inch, because the tip self-centers and starts cutting on contact.
Pilot point versus split point tips
A pilot point, also called a self-centering point, has a short sharp spike that bites into the work and keeps the bit from walking. A split point grinds the chisel edge of a standard twist drill into two cutting lips, which lowers the force needed to start a hole and removes the need for a center punch in most situations. Both designs help in metal, where a wandering bit ruins the hole and the workpiece.
Shank types and chuck compatibility
Round shank bits fit only in drill chucks. Some of the largest bits in a set carry three flat surfaces ground into the shank, a 3-flat design that lets chuck jaws grip without slipping, but they still will not work in an impact driver. Hex shank bits, by contrast, lock into impact drivers and quick-change chucks. Check the shank before you buy; a set that only works with a chuck is fine if every drill on the crew has one.
Fractional sets for metal work run from 1/16 inch up to 1/2 inch, and the most-used sizes are 1/8, 5/32, 3/16, 1/4, and 3/8 inch. A 14-piece set typically spans that range and covers fasteners up to roughly 1/2 inch. Metric sets mirror the same span in millimeters.
Matching Bits to Drills and Cordless Platforms
The brand-by-brand thinking that shows up in comparisons of cordless chainsaws from DeWalt, Makita, and Milwaukee applies to drills too. Each platform has its own battery, charger, and chuck ecosystem, and the accessory you pick has to work with the tool you already own.
Speed matters as much as the bit. A variable speed drill lets you start slow to seat the tip, then increase speed as the flutes engage. Cordless drills in the 12V to 20V class spin between 0 and about 2,000 RPM, which is plenty for steel, because metal drilling prefers lower speeds and firmer pressure than wood drilling. Impact drivers, despite the name, are not drills; they add rotational hammering and will snap round shank bits.
Chuck size and capacity
A 3/8 inch keyless chuck handles most twist bits up to 3/8 inch. A 1/2 inch chuck accepts the full range, including larger bits with 3-flat shanks. When you drill overhead or inside tight stud bays, a compact drill with a 3/8 inch chuck is easier to control, while a full-size 1/2 inch drill delivers more torque for larger holes.
Battery voltage and runtime
Higher voltage batteries deliver more torque, and larger amp-hour packs extend runtime. For occasional metal drilling, a 2 Ah pack is enough. For production runs, a 5 Ah pack cuts downtime. The battery you buy today also limits future tool purchases, so the platform decision matters as much as the bit.
Drilling Stainless Steel and Hard Metal: Step by Step
Stainless steel work-hardens: if the bit rubs instead of cutting, the surface gets harder and destroys the edge. The routine below prevents that failure.
- Mark the hole location and center punch it. The dimple gives the tip something to bite.
- Select the correct speed. Stainless drills at roughly half the speed of mild steel.
- Start the hole slowly with light pressure until the tip engages.
- Apply firm, steady pressure so the bit cuts continuously. Rubbing is what kills edges.
- Lift the bit every few seconds to break chips and let cutting fluid reach the tip.
- Ease off at breakthrough to avoid grabbing and snapping the bit.
Recommended speeds by material
| Material | Speed range (1/4 in bit) | Notes |
|---|---|---|
| Low carbon steel | 900-1,200 RPM | Use cutting oil |
| Stainless steel | 400-600 RPM | Slow feed, steady pressure, oil |
| Cast iron | 600-900 RPM | Dry or light oil; chips are abrasive |
| Aluminum | 1,500-2,500 RPM | Oil prevents gumming |
| Brass and bronze | 1,000-1,500 RPM | Light pressure, oil optional |
Speeds scale down as bit diameter grows. A 1/2 inch bit in steel turns at roughly half the speed of a 1/4 inch bit. Most cordless drills offer two gear ranges, and the low range is the right one for steel.
Lubrication choices
Cutting fluid does three jobs: it cools the edge, flushes chips, and lowers friction. Dedicated cutting oil works best on stainless. Thread cutting oil, paste lubricants, and even household oil beat running dry. For occasional work, a drop of oil on the hole every few seconds is enough.
Peck drilling deep holes
Holes deeper than three times the bit diameter trap chips and overheat the edge. Peck drilling, pulling the bit out every few seconds to clear chips, solves the problem. Keep a steady rhythm; consistent pecks keep the cut cool and the hole round.
Voltage Ratings, Maintenance, and Staying Informed
The voltage story behind cordless tools, including why DeWalt went 20V Max, explains why the numbers on the side of a drill do not always mean what they appear to. Marketing voltage, battery chemistry, and real-world torque all interact, and the same skepticism that applies to drill bit claims should apply to drill ratings.
A short maintenance routine keeps a cobalt set productive:
- Wipe bits clean and dry them after each job.
- Remove stuck chips from the flutes with a wire brush.
- Store bits in the original case so the edges do not knock together.
- Replace bits when the corners round over; resharpening cobalt is possible but shortens life.
- Never run a dull bit. A dull edge generates heat, not progress.
Safety belongs in the same routine. Wear eye protection, clamp small workpieces, and keep fingers clear of the spinning flute. Even established brands issue recalls, and the DeWalt 12-inch sliding compound miter saw recall is one example of why checking recall notices before buying and during ownership matters. A few minutes of verification protects both the tool budget and the crew.
A cobalt bit set earns its price when it matches the material you drill most. Read the fine print, check the shank, run the right speed, and the set pays for itself in holes that come out right the first time.