understanding the correct speed for your cobalt drill bit
is one of the most important factors for clean, precise holes and longer tool life.
Why Drill Speed Matters?
Speed truly matters - and not just how fast your drill spins. Many users buy cobalt drill bits expecting great results-but without the correct speed, even premium bits can dull quickly or burn the workpiece.Drill too fast, and you'll generate excess heat. Drill too slow, and cutting efficiency drops. Finding the right balance is essential for clean cuts and extended tool life.
What Does "Speed" Really Mean?
In drilling, speed means how fast the drill bit rotates (RPM), while feed refers to how quickly the bit advances into the material.
These two work hand-in-hand to determine cutting performance - this relationship is often called "Speeds and Feeds."
Understanding Speeds and Feeds
Speed (RPM): Controls cutting temperature.
Feed (mm/rev): Controls chip thickness and tool pressure.
Rule of thumb:
- Too high speed → overheating and dulling
- Too low feed → poor cutting efficiency
Recommended RPMs for Common Metals
Below is a simplified Cobalt Drill Bit Speed Chart, showing typical RPM ranges when using High-Speed Steel (HSS), Cobalt, and Carbide bits.
These are general guidelines for handheld or benchtop drilling up to 10mm diameter.
| Material | HSS Drill Bits (RPM) | Cobalt Drill Bits (RPM) | Carbide Drill Bits (RPM) |
|---|---|---|---|
| Aluminum | 2,400 – 3,000 | 2,000 – 2,800 | 1,800 – 2,500 |
| Brass | 2,000 – 2,500 | 1,800 – 2,200 | 1,500 – 2,000 |
| Copper | 2,000 – 2,500 | 1,800 – 2,200 | 1,500 – 2,000 |
| Mild Steel | 700 – 1,000 | 600 – 900 | 500 – 800 |
| Stainless Steel | 200 – 500 | 150 – 400 | 100 – 300 |
| Cast Iron | 300 – 800 | 250 – 700 | 200 – 600 |
💡 Tip: Faster speeds can be used when drilling softer materials such as wood, plastics, or composites.
(Data reference: TTP Hard Drills, Speeds & Feeds Calculator)
Don't Forget Pressure, Lubrication, and Cooling
Even at the right RPM, improper technique can ruin your bit.
Cobalt drill bits are designed for slow-speed, high-torque applications, but they still need help dissipating heat.
✅ Apply steady pressure – Let the bit do the work.
✅ Use cutting fluid or coolant – Prevents heat buildup and prolongs bit life.
✅ Drill at low speed – Especially for stainless steel or hard alloys.
✅ Clear chips frequently – Reduces friction and avoids jamming.
Cobalt vs High-Speed Steel: What Does "Speed" Mean Here?
You may have seen product names like "High Speed Steel (HSS) Cobalt Drill Bits" on marketplaces such as Amazon. The word "Speed" here does not mean how fast you should drill-it refers to the material's ability to withstand high cutting speeds.
HSS: More flexible, better for softer metals and general use.
Cobalt (M35/M42): Harder, more heat-resistant, ideal for tough alloys.
Your choice should depend on what you drill, not how fast you drill.
At Ceres Tools, we manufacture cobalt, HSS, and carbide drill bits with precise geometry and consistent quality control. Whether you're cutting mild steel or hardened stainless, we help you match the right bit to the right speed - so every hole is clean, precise, and repeatable.
Quick Takeaway
To achieve precise and efficient drilling:
🌀 Use the right RPM for your material
💧 Always lubricate and cool your bit
⚙️ Apply steady pressure
🕳️ Start with a pilot hole for larger diameters
By mastering these basics, you'll not only protect your tools but also produce smoother, cleaner holes in any metal.
References
Machinery's Handbook, 30th Edition (Industrial Press).
Multimax Direct - A Lazy Guide to Using Cobalt Drill Bits
Reddit - Cobalt vs HSS Drill Bits Discussion Thread
Related Reading
If you're not sure which drill size to choose, explore our expert guides:
4mm Drill in Imperial – Do You Really Need a Metric Conversion?
3.5 mm Drill Bits FAQ – Expert Advice from a Professional Machinist
Together, these articles form a complete resource for machinists and DIYers looking to make smarter drilling decisions.