---
title: "Which drill bit should I use for stainless steel?"
description: "A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting. The ranked options, the technique that changes the outcome,"
url: https://atoneplace.net/which/drill-bit-stainless-steel/
site: "At One Place"
---

# Which drill bit should I use for stainless steel?

**Which drill bit should I use for stainless steel?: A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting.**

Austenitic stainless steels work-harden aggressively: the deformation from a rubbing or skidding bit transforms the surface into a much harder layer, so the moment you stop cutting, the material becomes harder than the bit and the hole is effectively finished. This is why the technique is the opposite of instinct — slower speed and more pressure, never pausing to check progress mid-hole. Stainless also conducts heat poorly, so everything the cut generates stays in the cutting edge, which is what kills plain HSS. Run at roughly a third of the speed you would use in mild steel, keep flood or repeated lubrication going, and once a spot has been glazed, move to a fresh spot or grind the hardened layer away.

## The options, ranked

*Ranked best-first for the stated job. The third column is why the others exist.*

| Option | Good at | Bad at |
| --- | --- | --- |
| Cobalt (M35 or M42) bit | Retains hardness at the temperatures stainless generates, which plain HSS does not. | Brittle, so it snaps if the drill is allowed to wobble or the work moves. |
| Solid carbide bit | Cuts the hardest grades and holds an edge longest. | Needs a rigid setup — a drill press, not a hand drill — and shatters if it flexes. |
| Standard HSS bit | Will get through thin 304 sheet if it is sharp and well lubricated. | Blunts quickly, and once the surface is work-hardened it stands no chance. |
| Step bit | The most forgiving option for stainless sheet, avoiding the grab at breakthrough. | Thin material only. |

## Technique that changes the outcome

1. Run at about a third of mild-steel speed: often 300-500 rpm for small bits
2. Push hard enough that swarf comes off continuously, and keep pushing
3. Use a dedicated cutting fluid or heavy oil, applied constantly
4. Pilot-drill in one go rather than in stages that let the surface harden
5. Clamp the work solidly; any chatter hardens the surface and snaps a cobalt bit

## What goes wrong

- Pecking and pausing, which is exactly what work-hardens the surface
- High speed under the impression that it will cut faster
- Continuing on a spot that has glazed over — grind it back or start elsewhere

> Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.

## Other drill bit questions

| For | Use |
| --- | --- |
| Tile | A spear-point carbide or diamond bit in rotary mode only — hammer action shatters tile, every time. |
| Metal | An HSS twist drill, ideally with a 135° split point, run slowly with firm pressure and cutting fluid. |
| Concrete | An SDS-plus carbide bit in a rotary hammer — a normal hammer drill will get there eventually and blunt several bits doing it. |
| Masonry | A carbide-tipped masonry bit in hammer mode for brick and block; step up to an SDS rotary hammer above about 10 mm. |
| Porcelain tile | A diamond core bit, cooled with water, at low speed — carbide spear points do not cut porcelain. |
| Wood | A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom. |
| Plasterboard (drywall) | Almost none — an ordinary HSS or brad point bit in rotary mode, and the real question is which fixing goes in the hole. |
| Glass | A spear-point carbide or a diamond bit, run slowly under water — and toughened glass cannot be drilled at all. |
| Plastic | An HSS bit ground to a shallower rake, or a plastic-specific bit, at low speed with a backing board — acrylic especially will crack. |
| Hardened steel | Solid carbide in a rigid setup, or soften the spot first — HSS and cobalt cannot cut anything much above 50 HRC. |
| Aluminium | A sharp HSS bit at high speed with a wax or paraffin lubricant — the problem is aluminium sticking to the bit, not hardness. |
| Large holes in wood | Spade for speed and roughness, auger for depth, Forstner for a clean flat bottom, hole saw for big diameters in thin stock. |

## Common questions

### Which drill bit should I use for stainless steel?

A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting.

### What should I avoid?

Pecking and pausing, which is exactly what work-hardens the surface High speed under the impression that it will cut faster Continuing on a spot that has glazed over — grind it back or start elsewhere

## Related pages

- [Which drill bit should I use for tile?](https://atoneplace.net/which/drill-bit-tile/)
- [Which drill bit should I use for metal?](https://atoneplace.net/which/drill-bit-metal/)
- [Which drill bit should I use for concrete?](https://atoneplace.net/which/drill-bit-concrete/)
- [Which drill bit should I use for masonry?](https://atoneplace.net/which/drill-bit-masonry/)
- [Which drill bit should I use for porcelain tile?](https://atoneplace.net/which/drill-bit-porcelain-tile/)
- [Which drill bit should I use for wood?](https://atoneplace.net/which/drill-bit-wood/)
- [Which drill bit should I use for plasterboard?](https://atoneplace.net/which/drill-bit-plasterboard/)
- [Which drill bit should I use for glass?](https://atoneplace.net/which/drill-bit-glass/)
- [Which drill bit should I use for plastic?](https://atoneplace.net/which/drill-bit-plastic/)
- [Which drill bit will go through hardened steel?](https://atoneplace.net/which/drill-bit-hardened-steel/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)