Three grades, and the choice is not really about price. It is about what happens to the cutting edge when it gets hot, and how hard your steel is.
The three grades
| Grade | Use it on | The trade-off |
|---|---|---|
| M2 HSS | Mild and structural steel | Cheapest. Typically hardened to 65-66 HRC, often TiN coated. The only grade that resharpens |
| M42 cobalt (8%) | Stainless, duplex, high-tensile, anything that work-hardens | The cobalt holds the edge when the tip runs hot. Suppliers quote up to 30% more life than plain HSS |
| TCT (carbide-tipped) | Hardened, abrasive or weathered steel. High volume | Runs much faster. Suppliers claim 4-10x the life of HSS. Does not resharpen the same way |
Those life multiples are manufacturers’ own figures comparing grades, not brands, and there is no independent standard behind them. Treat them as direction, not measurement.
The speed difference is the part people miss
Carbide is usually sold on how long it lasts. In stainless, the more useful argument is how fast it runs.
| Diameter | HSS, rpm | TCT, rpm |
|---|---|---|
| 12 mm | 240 | 530 |
| 22 mm | 130 | 230 |
| 32 mm | 90 | 200 |
| 50 mm | 60 | 130 |
Recommended speed in stainless. Start at the low end of any range and work up.
530
240
230
130
200
90
130
60
0 rpm
Roughly twice the speed, in stainless, for the same hole. If you are drilling stainless in volume, that is a throughput argument before it is a tool-life one.
Why stainless is its own problem
Stainless work-hardens as you cut it. If the feed pauses, or the cutter spins without biting, the steel directly under the teeth gets harder than the teeth.
The cutter is then finished – and it will look like a quality problem when it was a technique problem.
Constant feed pressure and a sulphur-based or dedicated stainless cutting fluid do more for cutter life here than moving up a grade.
The resharpening question
An HSS cutter body can usually be reground several times on a standard tool grinder. Carbide-tipped cutters do not: the correct repair path there is replacement tips from the manufacturer if the body is sound.
If you have grinding capability in-house, or a supplier who does, that changes the arithmetic considerably – you are spreading one purchase over several lives. Worth asking about before you decide the cheaper grade is false economy.
A simple way to decide
- Mild and structural steel, ordinary volumes. HSS. Anything else is spending money on capability you will not use.
- Stainless, duplex, high-tensile. Cobalt at minimum. Carbide if the volume justifies it.
- Weathered, hardened or abrasive steel, or high volume of anything. Carbide.
- You genuinely do not know what the steel is. Say so when you enquire. It is a normal answer and it changes the recommendation.
Not sure which steel you are on?
Tell us what you are drilling, how thick, and how often. We will tell you which grade fits – and we will say so when the cheaper grade is the right answer.
Email info@neweratools.com or call +65 6241 0908.