Why Coatings Matter More Than You Think
A drill bit coating is not cosmetic — it is a functional layer that reduces friction, increases surface hardness, and extends tool life. The right coating can double or triple the number of holes you get from a single bit. The wrong coating wastes money without adding performance.
Here is what each common coating actually does, and when to specify it.
Bright Finish (Uncoated)
Bright finish means the HSS surface is polished but has no additional coating. The steel itself does all the work.
When to use it: Low-volume general purpose drilling in soft materials — aluminum, wood, plastic, mild steel. Bright finish bits are the lowest cost option and are easy to resharpen since there is no coating to damage.
Limitations: No heat protection beyond the base HSS grade. Chips tend to stick more in soft metals like aluminum.
Black Oxide
Black oxide is a chemical conversion coating (iron oxide, Fe₃O₄) applied through a steam tempering process. It creates a dark surface layer that reduces friction and provides mild corrosion resistance.
When to use it: General-purpose metalworking, especially in steel and cast iron. Black oxide reduces chip welding and provides about 50% longer life than bright finish in ferrous metals. It is also the most affordable coating option.
Limitations: The coating is thin (1–2 microns) and wears off relatively quickly under heavy use. It does not significantly increase surface hardness.
Amber (Bronze Oxide)
Amber coating is a variation of oxide treatment that provides similar benefits to black oxide with slightly better lubricity. The distinctive gold-brown color makes it easy to identify.
When to use it: Similar applications to black oxide. Popular in the North American market for jobber-length twist drills. Provides a good balance of performance and cost for general metalworking.
TiN (Titanium Nitride)
TiN is a PVD (Physical Vapor Deposition) coating that deposits a thin layer of titanium nitride onto the drill surface. It increases surface hardness to approximately 2,300 HV (Vickers) — roughly three times harder than uncoated HSS.
When to use it: Medium to high-volume production drilling in steel, stainless steel, and cast iron. TiN reduces friction by approximately 40%, allows higher cutting speeds, and typically delivers 3–5× the tool life of uncoated bits.
Cost consideration: TiN-coated bits cost 30–50% more than black oxide, but the extended tool life makes them more economical in production environments. The gold color also makes it easy to visually track wear.
TiAlN (Titanium Aluminum Nitride)
TiAlN is the premium PVD coating for high-performance drilling. It achieves surface hardness of 3,300+ HV and maintains performance at temperatures up to 800°C — significantly higher than TiN (600°C).
When to use it: High-speed CNC drilling, dry machining (no coolant), stainless steel, hardened steels, and abrasive materials. TiAlN forms an aluminum oxide layer at high temperatures that actually improves lubricity as the bit heats up.
Best pairing: TiAlN on M35 or M42 HSS creates a combination that handles the most demanding drilling applications short of carbide tooling, at a fraction of the cost.
Coating Comparison at a Glance
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Matching Coating to Application
Aluminum and non-ferrous metals: Bright finish or TiN. Avoid TiAlN — the aluminum content in the coating can cause chemical affinity with aluminum workpieces.
Mild steel and cast iron: Black oxide for low volume, TiN for production.
Stainless steel: TiN minimum, TiAlN preferred. Pair with M35 or M42 HSS.
Hardened steel (>30 HRC): TiAlN on M42 HSS. Consider split-point geometry to reduce thrust force.
Wood, plastic, composites: Bright finish is sufficient. Coatings add cost without meaningful benefit.
JacoTools Coating Capabilities
We offer all four coating options across our full range of twist drills, step drills, and hole saws. Our coating is applied after final grinding to ensure uniform coverage and proper adhesion. Every coated batch is tested for adhesion, thickness, and hardness before shipping.
Need a specific coating on a specific HSS grade? We can customize. Reach out at info@jacotools.com.
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