Pros and Cons of Cobalt vs HSS Drill Bits in Metalwork often decides whether your holes are clean, fast, and repeatable or slow, smoky, and costly. If you have ever glazed a bit on stainless or snapped a tip in cast iron, this guide will save you time and money. Pros and Cons of Cobalt vs HSS Drill Bits in Metalwork What each term really means in your toolbox Cobalt drill bits are high speed steel alloys with 5–8% cobalt added (commonly M35 or M42). The cobalt raises hot hardness and helps retain a sharp edge under heat. Standard high speed steel drill bits (HSS) are versatile and tough, ideal for general fabrication, wood-to-metal brackets, and mild steels. In short: cobalt favors heat resistance and hard metals; HSS favors toughness, affordability, and everyday use across softer metals. Where each bit type shines in practice Use cobalt for stainless steel, hardened steels, spring steel, and abrasive alloys where heat builds quickly. Choose HSS for mild steel, aluminum, brass, and short-run jobs where cost control matters. In job shops, cobalt excels on production runs of tough materials; HSS wins for prototypes, light fixtures, brackets, and field work. Both are available with split points and coatings to improve starts and chip flow. Key drawbacks you should expect Cobalt can be more brittle, so side-loading and misalignment risk chipping. It also costs more up front. HSS loses hardness faster when overheated and dulls sooner in tough alloys, increasing downtime. Using the wrong speed or skipping fluid can negate any advantage—especially on stainless, where work hardening punishes both bit types. Material science basics that drive performance Composition and alloying differences (M35/M42 vs HSS) M35 contains about 5% cobalt; M42 around 8%. More cobalt boosts red hardness and edge retention at elevated temperatures. Base HSS (without cobalt) remains a strong, tough tool steel, but its hot hardness ceiling is lower. For users, that means cobalt handles heat cycles better, while HSS absorbs shock and misalignment with less chipping risk. Heat resistance, red hardness, and edge retention Red hardness describes a tool’s ability to stay hard when red-hot. Cobalt alloys maintain a cutting edge longer at high temperatures, so they keep drilling rather than rubbing. Better edge retention reduces regrinds and preserves hole quality. HSS edges soften faster under heat, which is why lubrication and correct feeds are critical for longevity. Brittleness vs toughness: why it matters Toughness helps bits survive imperfect setups: handheld drills, wobbly fixtures, or off-center starts. HSS usually wins here. Brittleness increases with cobalt content, so machine rigidity, proper pilot holes, and straight alignment matter more. If you clamp well and drill on a press or mill, cobalt’s hotter hardness advantage shines without frequent tip chipping. Performance in real metalwork scenarios Stainless, cast iron, mild steel, and tool steel use-cases In stainless, cobalt drill bits cut cleaner and resist work hardening, especially when paired with a 135° split point and cutting fluid. In cast iron, both work, but cobalt edges last longer in abrasive microstructures. For mild steel and aluminum, HSS provides low-cost speed and acceptable life. In tool steels (annealed), cobalt maintains edge integrity for more holes per grind. Speed, feed, lubrication: dialing in the recipe Drop RPM for hard metals and keep a steady feed to avoid rubbing. Use cutting fluid or paste on stainless and tool steels to cool, lubricate, and clear chips. Peck drilling helps deep holes. Even with cobalt, running too fast overheats the edge. For softer metals, modest speeds and consistent feed keep HSS performing well with minimal chatter. Hole quality: walking, burrs, and precision Split-point tips (often 135°) reduce walking and lower thrust, improving accuracy. Proper clamping and center-punching also help. Burrs grow with dull edges and excessive speed; sharp bits and fluid minimize them. For reaming or tapping afterward, cleaner entry/exit holes cut rework. Both HSS and cobalt benefit from rigid fixturing to hold tolerance. Cost, longevity, and shop ROI Upfront price vs lifespan over time Cobalt costs more per bit but often costs less per hole in tough metals due to superior edge life. HSS has a low entry price, ideal for small batches, field kits, and casual use. For repeat stainless jobs, cobalt’s durability repays quickly; for mixed materials and occasional drilling, HSS keeps budgets lean. Sharpening potential and maintenance intervals Both types can be resharpened. Cobalt holds geometry longer but needs careful grinding to avoid overheating the cutting lips. HSS grinds quickly and is more forgiving. Using a jig or dedicated sharpener keeps angles consistent and extends service life, lowering total tooling cost. Calculating total cost per hole Track holes per grind, grinds per bit, labor time, and scrap rate. Add consumables like fluid. If cobalt delivers twice the holes in stainless with fewer rejects, its higher buy-in is justified. In mild steel, HSS may deliver the best cost per hole, especially in low-volume shops. How to choose the right bit for your job A quick decision matrix by material and volume For stainless, tool steels, or frequent production: choose cobalt. For mild steel, aluminum, brass, or occasional work: choose HSS. High-volume runs favor cobalt’s consistency; one-off or on-site repairs favor HSS economy. Match the decision to material hardness, part count, and your setup’s rigidity. Geometry and coatings: split points, 135°, TiN, and more A 135° split point reduces thrust and walking, especially on stainless. Coatings like TiN, TiAlN, or black oxide improve chip flow and heat shedding. They are helpful but not magic—correct RPM and feed remain the keystone. Select parabolic flutes for deep holes and consider step drilling on large diameters. Safety and best practices to extend tool life Clamp the work, use eye protection, and avoid side-loading. Apply cutting fluid on ferrous metals, especially stainless. Keep speeds appropriate: slower for hard alloys, faster but controlled for soft. Back the bit out to clear chips. These habits protect both cobalt and high speed steel drill bits from premature failure. Care, storage, and troubleshooting Sharpening angles, jigs, and when to retire a bit Maintain a consistent point angle (118° for general use, 135° for harder metals) with equal lip lengths and correct clearance. A bench grinder with a jig or a dedicated sharpener is ideal. Retire bits with burned margins, deep chipping, or uneven wear that repeated grinding cannot correct. Avoiding work hardening and heat damage Use steady feed and adequate lubrication on stainless to prevent rubbing. If you see blue chips or hear squealing, reduce speed and increase feed slightly. Peck to break chips on deep holes. Even with the Pros and Cons of Cobalt vs HSS Drill Bits in Metalwork in mind, technique is the ultimate life extender. Common failure modes and quick fixes Walking: switch to a split point or center-punch first. Chatter: clamp better and reduce RPM. Burned edges: slow down, add fluid, and resharpen. Chipping on cobalt: improve alignment and reduce side pressure. For background on geometries and types, see this drill bit overview. For more comparisons and practical picks, explore our in-depth category page: Tool Reviews & Comparisons. The Pros and Cons of Cobalt vs HSS Drill Bits in Metalwork come down to matching material, speed, and budget—choose accordingly. Want more tools, tips, and trusted gear? Explore all our expert guides and curated picks HERE.
