The Enemy: Work Hardening
Stainless Steel (especially 304 and 316 grades) has a nasty property called Work Hardening. As you heat it up with friction, its crystal structure changes and it becomes harder.
If you run your drill too fast (High RPM) and don't apply enough pressure, you are just rubbing the metal, creating heat. You are literally hardening the steel while trying to cut it. Moments later, your drill bit glows red and dies.
The Titanium Coating Myth
Many DIYers buy "Gold" drill bits labeled "Titanium", thinking they are made of Titanium. They are not.
They are usually cheap High Speed Steel (HSS 4241) with a microscopic layer of Titanium Nitride (TiN) paint.
The problem: The moment you start drilling stainless steel, that coating wears off the tip. You are left with soft, cheap steel against hard stainless. It's a recipe for failure.
Why Cobalt is King (M35 vs M42)
For stainless steel, you need Cobalt Drill Bits. Unlike coatings, Cobalt is melted into the steel alloy itself.
- M35 (5% Cobalt): The industry standard. Enhances "Red Hardness" (ability to stay hard at high temps). Best value for pros.
- M42 (8% Cobalt): Even higher heat resistance. Harder, but more brittle. If you use a hand drill and wobble, M42 might snap. Best for drill presses.
RPM Guide for Stainless
Slow Down! You must drill stainless at 50% the speed of mild steel.
| Bit Size | RPM (Mild Steel) | RPM (Stainless) |
|---|---|---|
| 3mm (1/8") | 2500 | 1200 |
| 6mm (1/4") | 1200 | 600 |
| 10mm (3/8") | 800 | 400 |
| 13mm (1/2") | 600 | 300 |
