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Stainless steel is harder to drill than mild steel, and it punishes a dull or overheated bit quickly. The choice usually comes down to cobalt bits or standard high-speed-steel bits with a titanium coating. For repeated holes, thick stock, or unknown stainless, cobalt is the safer buy. For occasional holes in thin sheet, a sharp titanium-coated bit can work—if you keep it cool and don’t expect the coating to make an ordinary bit indestructible.
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The short answer
Choose a cobalt drill bit set for stainless steel you’ll drill more than occasionally, especially when the material is thick or the grade is unknown. Cobalt bits are made from high-speed steel alloyed with cobalt; the alloy runs hotter without losing hardness as quickly. The cobalt is part of the bit, not a surface layer, so sharpening the cutting edge does not remove it.
A titanium-coated HSS bit set is a reasonable lower-cost choice for a few holes in thin stainless sheet. “Titanium” usually means a thin titanium-nitride coating on a high-speed-steel bit. It can reduce friction when new, but it does not turn a basic bit into a cobalt bit. Once the cutting edge is ground or the coating wears through, the underlying steel determines performance.
How the bits compare
| Feature | Cobalt HSS | Titanium-coated HSS |
|---|---|---|
| Construction | Cobalt alloy throughout the bit | HSS core with a thin surface coating |
| Stainless performance | Better suited to repeated holes and tougher stock | Can handle occasional holes in thin stock with careful technique |
| Sharpening | Can be sharpened and used again | Can be sharpened, but sharpening removes coating at the edge |
| Cost | Usually more per bit | Usually cheaper as a general-purpose set |
| Main failure risk | Overheating, dulling, or chipping from poor technique | Coating wears; the HSS edge overheats or dulls on stainless |
Cobalt is not immune to bad technique. A cobalt bit can burn up, work-harden the steel, or snap if it rubs instead of cutting. Its advantage is a more heat-resistant cutting edge—not permission to run the drill at full speed.
Choose by the job
For a bracket, sink, exhaust component, or other part with several holes, cobalt is worth the extra cost. It is also the better choice for stock around 1/8 inch thick or more, though thickness alone does not determine difficulty: stainless grade, work hardening, and whether the workpiece is supported all matter. For just one or two holes in thin sheet, a sharp titanium-coated bit is acceptable if you can control speed and pressure. If it stops cutting cleanly, don’t keep forcing it; switch to a fresh bit.
Look for cobalt HSS marked M35 for a practical general-purpose choice. M42 contains more cobalt and can tolerate higher heat, but it is also harder and more brittle; for hand-drill work, M35 is often the more forgiving pick. Avoid assuming that a set advertised as “titanium” is suitable for stainless just because it contains many sizes. Check that it is HSS and treat it as a budget option, not a specialist stainless-steel bit.
Drilling technique matters more than the label
Secure the workpiece in a vise or clamp it firmly. Do not hold a stainless part in your hand while drilling. Mark the hole, then use a center punch to keep the bit from wandering. For holes larger than about 1/4 inch, start with a smaller pilot hole—roughly 1/8 inch is a useful starting size—then step up. A pilot hole helps the larger bit cut without wandering, but it does not excuse running it too fast.
Use a cordless drill in low gear, or a drill press if available. For common bit sizes in stainless, a slow range around 300–800 rpm is a sensible starting point; use the lower end for larger bits. The exact safe speed depends on diameter and the material, so watch the chips and adjust. Apply steady pressure so the bit cuts and produces small chips. If you see smoke, hear squealing, or get a polished spot with no chips, stop. Those are signs of excess heat or rubbing, and stainless can work-harden into a tougher layer that makes the next attempt harder.
Use cutting oil or a lubricant made for drilling metal. Add it at the cutting point and reapply as needed. For a deep hole, drill a short distance at a time and withdraw the bit to clear chips and let heat escape. Let the bit cool if it becomes too hot to touch safely; don’t dunk a hot bit in water, which can risk thermal damage. A sharp bit, low speed, firm feed, and lubrication are a better combination than simply buying the most expensive set.
Common mistakes and what to buy
The most common failure is running a small cordless drill at high speed with light pressure. The bit rubs, the edge overheats, and stainless hardens where you need to cut. Another is using a worn bit because it “still looks fine.” A dull edge needs more force and heat, increasing the chance of a snapped bit or a ruined workpiece. Replace a cheap bit that no longer cuts; sharpen a cobalt bit only if you can maintain the correct cutting angle.
If you’re buying one set for workshop use, choose a cobalt set covering the sizes you need, and keep cutting oil nearby. If the budget is tight and the job is a couple of holes in thin sheet, use a sharp titanium-coated set you already own before paying for cobalt. But don’t buy a large titanium-coated assortment expecting it to replace cobalt for repeated stainless work. For a hole that must be clean and accurately placed, clamp the work, start with a punch mark, and use a drill press when practical; the machine helps control alignment, but it cannot compensate for a dull bit or excessive speed.