Cobalt Drill Bits vs. HSS vs. Carbide: Which One Fits Your Metal Job?

Your standard twist bit skates across stainless, squeals as it heats up, then comes out blue, dull, or broken before the hole is finished. That failure costs more than a bit. It can work-harden the metal and turn a simple repair into a stalled project.

Cobalt drill bits are one fix, but they are not the only one, and they are not always the right one. Standard HSS, cobalt, and carbide each win in different shops. Below you get the three compared by heat tolerance, toughness, cost, and machine, the M35 vs. M42 call, and a speed and coolant matrix for common metals.

Are Cobalt Drill Bits Good?

Short answer: yes. Cobalt drill bits are good for stainless steel, cast iron, tougher alloys, and repeated metal drilling. The cobalt is alloyed throughout the steel, so the cutting edge keeps its heat resistance as it wears.

They are not the best pick for every job. Standard HSS handles softer metals and occasional holes for less money, and carbide can beat cobalt on a rigid, high-volume setup. A quick way to sort it out:

• Occasional holes in aluminum or mild steel: standard HSS is usually enough.
• Stainless, cast iron, alloy steel, or many holes: cobalt, usually M35.
• Hard or abrasive material on a rigid drill press: carbide.

Cobalt Drill Bits Are an Alloy, Not a Coating

A gold-colored drill bit is not automatically a cobalt bit. True cobalt drill bits get their performance from the metal throughout the tool, not from a colored surface treatment.

Cobalt bits are high-speed steel (HSS) alloyed with cobalt during manufacturing. The two common grades are M35, with about 5% cobalt, and M42, with about 8% cobalt. The cobalt improves hot hardness, so the edge stays sharp as drilling heat climbs.

That differs from titanium-coated HSS. A titanium coating can cut friction while it lasts, but it sits only on the surface. Once the edge wears or you resharpen it, most of that benefit is gone. Cobalt stays in the steel all the way through.

M35 vs. M42: Which Cobalt Grade Do You Need?

More cobalt is not automatically better. M42 offers more heat resistance and wear life, but it is less forgiving of flex, runout, and side loading than M35. Match the grade to your equipment:

• M35 cobalt: a more forgiving choice for handheld drills, garage work, repair jobs, and setups with minor chuck runout or tool flex.
• M42 cobalt: better suited to rigid drill presses, controlled feeds, and repeated drilling in hard metals. Avoid forcing the bit or applying side load.

When you compare listings, look past color. Confirm the stated M35 or M42 grade, a 135° split point to help the bit start accurately and resist walking, and the size range you need. The listing should say cobalt-alloy HSS, not just a cobalt-colored finish.

Our 29-piece cobalt drill bit set covers 1/16 to 1/2 inch by 64ths with a 135° split point, and you can find it in our drill bits collection.

Standard HSS vs. Cobalt vs. Carbide Drill Bits

Hardness alone does not choose the right bit. Your drill also has to control flex, runout, and vibration. This table compares the three on the factors that decide most purchases.

Standard HSS is the economical option for softer metals and occasional drilling. It tolerates minor flex and imperfect handheld technique better than harder bit materials, but sustained heat dulls it quickly in stainless steel and cast iron.

Cobalt earns its higher cost when standard HSS keeps losing its edge in tougher metals. Because the alloy runs through the bit, sharpening exposes fresh cobalt. Pair it with the right speed, steady feed pressure, and cutting fluid, especially in stainless.

Carbide is harder and more wear resistant than cobalt, but it is not an automatic upgrade. It needs rigid fixturing, low chuck runout, and vibration control. In most home garages and field repairs, cobalt is the safer choice, because a handheld drill can move enough to chip a carbide edge.

Cobalt vs. Carbide Drill Bits for Stainless Steel

Choose cobalt for handheld drilling, lightly rigid drill presses, and repair work. Choose carbide only with a stable drill press or CNC-style setup, where secure clamping, alignment, and controlled feed justify the higher fracture risk.

Drill Speed and Coolant Matrix for Common Metals

A stainless bracket is a classic trouble spot: the bit turns blue, the hole stops advancing, and more speed only makes the squeal worse. Metal drilling usually fails from excess heat and rubbing, not because the bit is too soft.

Use this matrix as a starting point, then adjust for the bit maker's guidance, drill rigidity, hole depth, and chip clearing. SFM means surface feet per minute, the speed at the cutting edge of the bit.

How to Calculate RPM From SFM

RPM = (SFM × 3.82) ÷ drill diameter in inches

A 1/4-inch cobalt bit in 304 stainless runs about 535 RPM at 35 SFM and 765 RPM at 50 SFM. Treat every figure as a starting point, not a maximum, and slow down if the bit heats up.

Stainless steel warning: use low RPM, steady positive feed, and coolant. A bit that makes little or no chip is rubbing instead of cutting. Stop, add lubricant, and restore firm feed pressure before the surface work-hardens.

For holes larger than your drill chuck can hold, Silver and Deming drill bits keep a 1/2-inch shank so a standard chuck can drive the bigger diameter.

How to Drill Clean Holes in 304 Stainless Steel

Picture a 1/4-inch mounting hole in a 304 stainless bracket. The bit squeals, the surface turns shiny, and progress stops. More RPM will not fix it. A controlled setup keeps the bit cutting instead of rubbing.

1. Mark, punch, and clamp the location. Center-punch the mark to give the bit a starting seat. Clamp the bracket to a drill-press table or solid workbench. Never hold stainless steel by hand while drilling.
2. Select the bit and starting hole. For most handheld or drill-press jobs, use a 1/4-inch 135° split-point M35 cobalt bit. The split point helps prevent walking. For a larger finished hole or a less rigid setup, drill a smaller pilot hole first.
3. Set a conservative speed and add fluid. For 304 stainless, use the matrix range of about 535 to 765 RPM with a 1/4-inch bit. Apply cutting oil or stainless-compatible tapping fluid, then start the drill square to the workpiece.
4. Feed positively, not forcefully. Apply enough pressure to produce a continuous chip. If the bit spins without making chips, it is rubbing and can work-harden the surface. Excessive side pressure can break a cobalt bit or chip a carbide bit.
5. Peck deeper holes as needed. Withdraw the bit briefly to clear chips and refresh lubricant, then resume drilling. Do not let the bit dwell in the hole while spinning.

Stop and correct the setup if any of these appear:

• The bit squeals
• Smoke appears
• Chips turn blue
• The flutes stop producing chips
• The bit begins to wander

Stop the drill, add lubricant, reduce RPM if needed, and restart with a square, steady feed. Wear safety glasses, keep the workpiece clamped, and use a brush, not your hands, to clear chips.

If you are weighing coatings against alloys, our guide to titanium vs. cobalt drill bits breaks down that choice.

Resharpening Cobalt Drill Bits

A dull cobalt bit is not automatically a worn-out bit. Because cobalt runs through the alloy, resharpening does not remove its heat-resistant benefit the way grinding a TiN-coated HSS bit removes the coating.

Use a white or pink aluminum-oxide wheel or a CBN wheel rated for the tool material. Make light passes and let the bit cool between them. Restore equal cutting lips, the original 135° point angle, and split-point geometry where applicable. Unequal lips make one side cut harder, causing wandering, chatter, or oversized holes.

Overheating is the most common sharpening mistake. Blue, straw, or dark discoloration at the point signals heat that can soften the edge. A bit may look sharp after grinding but dull quickly if the cutting edge was burned. Replace rather than resharpen cobalt drill bits that are:

• Chipped, cracked, or repeatedly breaking
• Badly overheated or heavily discolored
• Too short to sharpen safely and accurately

Choosing Cobalt Drill Bits Only When the Job Calls for Them

Start with the material, machine, and volume of work, not the highest-priced bit. Standard HSS is enough for occasional holes in aluminum, mild steel, and other softer metals. Its lower cost and tolerance for minor flex make it a sensible handheld-drill choice.

Step up to cobalt drill bits for stainless steel, cast iron, tougher alloys, or repeated drilling. For typical garage work and handheld drills, M35 is the practical middle ground. Choose M42 only when a rigid, well-aligned drill press can hold a controlled feed. Reserve carbide for very hard material and a securely clamped workpiece on a rigid machine, since its brittleness can waste a costly bit before the hole is finished.

Before you buy, list each hole size, match it to the material and machine, and set speed, fluid, and pressure from the matrix above. Shop HSS jobber drill bits for everyday holes in steel and aluminum.

Frequently Asked Questions

Are cobalt drill bits good?

Yes. Cobalt drill bits are an excellent upgrade for stainless steel, cast iron, tougher alloys, and repeated metal drilling. They hold their cutting edge under heat better than standard HSS because cobalt is alloyed throughout the tool. They are not necessary for every job. Standard HSS is usually enough for wood, plastic, aluminum, and occasional holes in mild steel.

Are cobalt drill bits better than HSS drill bits?

Cobalt bits are upgraded HSS, not a separate material. The cobalt alloy improves heat resistance and edge retention, which helps in stainless steel, hard metals, and long drilling sessions. Standard HSS remains the economical choice for softer metals and is more forgiving of minor drill movement in basic handheld jobs.

Cobalt vs. carbide drill bits for stainless steel: which is better?

Cobalt is usually better for stainless steel with a handheld drill or a typical home-shop drill press. It resists heat well and tolerates slight flex, vibration, and imperfect alignment better than carbide. Carbide suits rigid drill presses, CNC-style machines, and securely clamped production work, but it can chip or break when the setup has runout, side load, or vibration.

Can I drill stainless steel with cobalt bits without cutting oil?

You can, but it is not recommended. Dry drilling creates more heat, increases rubbing, and raises the risk of work-hardening the stainless before the hole is complete. Use cutting oil or stainless-compatible tapping fluid, slower RPM, and steady feed pressure that produces chips.

Can cobalt drill bits be sharpened?

Yes. The cobalt alloy runs through the entire bit, so resharpening restores the edge without removing the heat-resistant material. Use a suitable wheel, make light passes, and keep equal cutting lips with the original 135° point geometry. Replace bits that are cracked, heavily overheated, or too short to sharpen safely.