We are tired of marketing claims about “unbreakable” drill bits, so we put five popular sets through a standardized torture test on our Haas VF-2SS and counted every single hole until each bit either broke or lost tolerance. No sponsored content, no manufacturer input — just steel, coolant, and a tally sheet.
Testing Methodology
We drilled 5/16-inch (8 mm) through-holes in 12 mm thick 4140 pre-hardened steel (28-32 HRC) at 2,500 RPM and 6 IPM (0.0024 IPR), with flood coolant at 8 percent concentration. Each bit was clamped in the same 3/8-inch hydraulic chuck with less than 0.0002 inches of runout. We peck-drilled with a 1xD peck depth to keep chip evacuation consistent across all tests. A fresh coolant charge was mixed for each bit to eliminate any variable from coolant degradation.
A hole was considered a failure when it exceeded +0.002 inches on diameter (checked every 10 holes with a pin gauge set) or when the bit physically broke. We also tracked three qualitative metrics: hole quality (burr formation and wall finish), walking tendency on entry, and heat discoloration of the chips and workpiece.
The Five Contenders
Brand A: Budget HSS-Cobalt Set ($28 for 13-piece) — A big-box store staple with 5 percent cobalt content and a standard 118-degree split point. Gold oxide coating.
Brand B: Mid-Range Cobalt Set ($52 for 13-piece) — An industrial supplier brand with 8 percent cobalt (M42 grade), 135-degree split point, and no additional coating. Bright finish.
Brand C: TiAlN-Coated HSS Set ($45 for 13-piece) — Standard M2 HSS with a titanium aluminum nitride PVD coating. 135-degree split point.
Brand D: Solid Carbide Jobber ($18 per bit) — A single solid carbide bit with a 140-degree split point and AlTiN coating. The most expensive option by far.
Brand E: Premium M42 Cobalt Set ($74 for 13-piece) — Industrial-grade M42 with 8 percent cobalt, 135-degree split point, heavy-duty web thinning, and a parabolic flute design for improved chip evacuation.
Results
| Brand | Holes Before Failure | Failure Mode | Hole Quality (1-10) | Walking (1-10) | Heat Discoloration |
|---|---|---|---|---|---|
| Brand A (Budget Cobalt) | 92 | Gradual dulling, oversized at hole 92 | 5 | 6 | Moderate blue chips after hole 50 |
| Brand B (Mid-Range Cobalt) | 165 | Corner chipping, gradual tolerance loss | 7 | 8 | Light straw chips throughout |
| Brand C (TiAlN HSS) | 68 | Coating failure, rapid softening | 4 | 7 | Heavy blue discoloration after hole 40 |
| Brand D (Solid Carbide) | 311 | Catastrophic fracture on hole 311 | 9 | 10 | Minimal, silver chips throughout |
| Brand E (Premium M42) | 285 | Gradual wear, oversized at hole 285 | 8 | 9 | Light straw chips, no blue |
The Winner: Brand E (Premium M42 Cobalt)
The Brand E premium M42 cobalt set is our clear winner for the vast majority of shop applications, and here is why. While the solid carbide bit drilled 26 more holes, it failed catastrophically — no warning, no gradual wear, just a sudden snap on hole 311 that left a broken bit embedded in the workpiece. We spent 15 minutes carefully extracting it with an EDM sinker. In a production environment on a manual mill or drill press, that kind of failure can damage the workpiece, the holder, or the operator’s confidence.
The Brand E M42 bit, by contrast, showed textbook predictable wear. Holes 1 through 200 were virtually identical in quality. From holes 200 to 260, we noticed a slight increase in burr height on the exit side. By hole 270, the pin gauge was starting to feel looser. At hole 285, we exceeded our +0.002-inch tolerance. That kind of gradual, predictable degradation is exactly what you want in a production tool — it gives you time to plan your tool change instead of reacting to a disaster.
The 135-degree split point combined with the heavy web thinning meant the Brand E bit self-centered almost as well as the solid carbide. Walking was less than 0.003 inches on a center-punched start, compared to 0.008 inches for the budget Brand A set.
What Surprised Us
The TiAlN-coated HSS set (Brand C) was the biggest disappointment. At $45, it is priced to suggest serious performance, but the underlying M2 HSS substrate simply cannot handle the temperatures that build up in 4140 steel. Once the coating wore through — which happened around hole 35 to 40 based on the color change in the chips — the bit degraded rapidly. By hole 68, it was pushing material more than cutting it.
We were also surprised by how well the budget Brand A cobalt set performed for its price point. At $28 for a 13-piece set, getting 92 holes in pre-hardened 4140 is respectable. For occasional use in a maintenance shop or home garage, it is hard to argue against the value.
Buying Recommendations
For production shops drilling steel or stainless daily: Brand E premium M42 cobalt. The predictable wear pattern and 285-hole life make it the clear choice. At roughly $5.70 per bit, the cost per hole is under two cents.
For dedicated CNC operations with rigid setups: Solid carbide (Brand D). If you have a stable spindle, a hydraulic chuck, and through-spindle coolant, the 311-hole count and superior hole quality justify the $18 per-bit cost. Just plan your tool changes based on hole count, not wear observation.
For occasional use and maintenance work: Brand A budget cobalt. Ninety-two holes for $2 per bit is excellent value when you are drilling a handful of holes a week.
Skip entirely: TiAlN-coated HSS (Brand C). The coating creates a false sense of premium performance over a substrate that cannot back it up in demanding materials.