Drilling Guide
Drill Bit Types Explained: HSS vs Cobalt vs Carbide
Three tool grades, three very different speed and durability profiles — here's which one actually earns its price for your material.
The drill bit material sets the ceiling on how fast you can cut and how much abuse the edge can take before it dulls. Choosing the wrong grade either wastes money on unnecessary carbide, or wastes time babying an HSS bit through a material it isn't suited to.
See the speed difference for your setup
Switch drill type in the calculator and watch the RPM recalculate instantly.
The three grades, side by side
| Drill grade | Relative cost | Practical speed vs HSS | Toughness | Best materials | Rigidity needed |
|---|---|---|---|---|---|
| HSS | Low | 1× baseline | Most forgiving of shock | Mild steel, aluminium, brass | Secure manual or machine setup |
| Cobalt (M35/M42) | Medium | About 1.5× in this calculator | Tough, but less forgiving than plain HSS | Stainless and alloy steels | Stable setup; avoid flex and runout |
| Carbide | High | About 4× in this calculator | Hard and wear-resistant; brittle | Cast iron, abrasive alloys; harder steels with suitable tooling | Rigid machine, low runout, controlled feed |
Speed ratios are simplified calculator assumptions, not maximum ratings. Actual practical limits depend on the alloy, coating, geometry, coolant and machine; use the drill manufacturer’s data rather than applying a fixed multiplier to every job.
Carbide vs cobalt drill bits
Cobalt HSS (M35 or M42) is usually the more forgiving choice on a pillar drill or manual mill, particularly for stainless steel. Carbide can support higher cutting speeds in a rigid machine, but a flexible setup or interrupted entry can chip its edge. Choose by workholding and tool guidance as well as material. Compare starting RPM in the drill speed chart, then enter your settings in the drilling calculator.
HSS — the workshop default
High-speed steel is the standard, affordable choice for most jobs. It holds an edge well enough for mild steel, aluminium and brass, and tolerates a bit of vibration or an imperfectly clamped workpiece better than harder, more brittle tool grades.
Cobalt — for tougher materials
Cobalt drills add a cobalt alloy to the steel, which keeps the cutting edge hard at higher temperatures. That lets them run roughly 1.5× faster than HSS and resist the heat buildup that causes rapid dulling in stainless steel and other tough alloys. See the speeds and feeds guide for exactly how that multiplier changes your RPM.
Carbide — speed and volume
Carbide holds an edge far longer than HSS or cobalt and can run several times faster, but it's brittle — a poorly secured workpiece, excessive vibration, or an interrupted cut can chip or snap a carbide drill that an HSS bit would shrug off. It earns its cost in production runs and harder or more abrasive materials where tool life and cycle time matter more than upfront cost.
Frequently asked questions
What is the difference between HSS and cobalt drill bits?
Cobalt drills contain a cobalt alloy that keeps their hardness at higher temperatures than plain HSS, allowing roughly 1.5× faster cutting speeds and better performance in tougher materials like stainless steel.
When should I use carbide drill bits?
Carbide runs several times faster than HSS and holds an edge far longer, but is more brittle and less tolerant of vibration. It suits high-volume production and harder or more abrasive materials.
Are cobalt drill bits worth the extra cost over HSS?
For stainless steel and harder alloys, yes — the extra speed and heat resistance usually pay for themselves in tool life. For soft materials like aluminium, standard HSS is usually sufficient.