Selecting the best drill bits for drilling stainless steel?

Stainless steel can be a nightmare if you don't have the right tools. I remember ruining a whole sheet of it once before I learned the secret. Want to avoid the same frustration?

The best drill bits for stainless steel are cobalt bits with a 135-degree split point. They resist heat better, stay sharp longer, and cut more efficiently than standard HSS or titanium-coated bits.

Let me share what I've learned after years of working with stainless steel. These insights will save you time, money, and a lot of headaches.

Is it better to drill stainless steel fast or slow?

You might think faster drilling saves time, but with stainless steel, that thinking can backfire. I learned this lesson the hard way on an important project. What speed works best?

Drilling stainless steel should be done slowly with consistent pressure. Slow speeds (around 300-400 RPM) prevent work hardening and excessive heat buildup that makes the material more difficult to cut.

The relationship between drilling speed ¹and success with stainless steel is something I've studied extensively in my production facility. When drilling too fast, the friction creates tremendous heat that not only dulls your bit quickly but actually changes the material properties of the stainless steel. This phenomenon called "work hardening" makes the steel tougher and more resistant to cutting as you drill.

[1]Finding the right drilling speed is essential for achieving precision and prolonging bit life in stainless steel applications.

I've found the sweet spot is typically between 300-400 RPM for most stainless steel applications. At this speed, the cutting edges have time to remove material without generating excessive heat. Using cutting oil further reduces friction, extending bit life significantly. In our tests comparing slow versus fast drilling speeds, bits lasted 3-4 times longer at slower speeds, and the finished holes were more precise with less burring around the edges.

Remember that consistent pressure is just as important as speed. Let the drill do the work without forcing it, and you'll get much better results.

Are cobalt or titanium drill bits better for stainless steel?

I've spent thousands on different drill bits over the years, trying to find the perfect match for stainless steel. Between cobalt and titanium, there's a clear winner, but the reason might surprise you.

Cobalt drill bits outperform titanium bits for stainless steel. Cobalt bits contain 5-8% cobalt blended throughout the metal, providing heat resistance up to 1100°F. Titanium bits only have a surface coating that wears away quickly on tough stainless steel.

The difference between cobalt and titanium bits becomes apparent after drilling just a few holes in stainless steel. In our manufacturing facility, we conducted extensive testing comparing M35 cobalt bits (containing 5% cobalt) and M42 bits (containing 8% cobalt) against titanium-coated HSS bits.

The results were striking: the titanium coating, while initially very hard, began to wear off after just 5-7 holes in 304 stainless steel. Once this happens, the underlying softer HSS material dulls quickly. In contrast, the cobalt bits maintained their cutting edge much longer - in some cases, a single M42 bit drilled over 50 holes before requiring resharpening.

The key difference is that cobalt is alloyed throughout the entire bit, not just coated on the surface. This means even as the bit wears, fresh cobalt material is exposed, maintaining the bit's heat resistance and hardness. We found the M42 cobalt bits, though more expensive initially, provided the lowest cost per hole when working with stainless steel.

That said, for very occasional use, titanium bits might be adequate, but for any serious work with stainless steel, cobalt is the clear winner.

What is the trick to drilling stainless steel?

There's a simple trick to drilling stainless steel that changed everything for me. Before I discovered it, I was constantly fighting with dulled bits and ragged holes. Want to know the secret?

The trick to drilling stainless steel is using a pilot hole, applying cutting fluid, maintaining consistent pressure, and clearing chips frequently. These steps prevent work hardening and ensure clean, precise holes without damaging your bits.

From my experience running a drill bit manufacturing company, the most important trick is the comprehensive approach to the drilling process itself. Start with a center punch to mark the exact drilling location, preventing the bit from "walking" across the hard surface. Then drill a small pilot hole (about half the diameter of your final hole) which reduces the resistance for the larger bit.

Cutting fluid is absolutely essential - I prefer sulfur-based fluids specifically formulated for stainless steel, as they form a barrier between the bit and material that reduces friction dramatically. Apply it generously and frequently throughout the drilling process.

The pressure you apply matters tremendously. Too little and the bit rubs without cutting, generating heat. Too much and you risk breaking the bit. The ideal pressure allows the bit to cut continuously without stalling. I teach our customers to listen to the sound - a consistent cutting sound without squealing indicates proper pressure.

Finally, the "peck drilling"¹ technique has saved countless bits in our workshop. This involves periodically retracting the bit to clear chips and allow cutting fluid to reach the cutting edge. With stainless steel, I recommend retracting every 3-4mm of depth to clear chips and reduce heat buildup.

[1] Learn how peck drilling can save bits and improve the quality of your drilling work.

By combining these techniques, even tough stainless steel becomes manageable to drill, with clean holes and extended bit life.

Conclusion

For drilling stainless steel successfully, choose cobalt bits, use slow speeds with cutting fluid, maintain consistent pressure, and regularly clear chips. These practices will give you clean, precise holes every time.