Greetings. I wonder if someone can educate me a bit more about quality drill bits. I have recently learned the term "high speed steel" can mean several different alloys. In the US it tends to mean M2 which has 6% tungsten, 5% molybendum, 4% chromium and 2% vanadium. It can also mean T1 which means 18% tungsten, 4% chromium and 1% vanadium, though T1 is much less often used because of the relative expense of tungsten.
In China, unless otherwise indicated, "high speed steel" seems to be "4341" or "4241" meaning 4% tungsten, 2% or 3% molybendum, 4% chromium and 1% vanadium. They generally rely on the titanium nitride coating to make up for the inferiority of the steel alloy relative to M2.
M35 adds 5% cobalt and M42 adds 8% cobalt to the alloy to make bits more suited for drilling in hard metal.
To their credit, the Chinese manufacturers are at least honest about what alloy they use. It's like pulling teeth to get this info from the major brands.
There is also the question about how the bits are made, roll forged, edge ground or fully ground, the latter being the best. One question I have is whether one can visually distinguish between the processes. All bits I know to be roll forged seem to have a raised ridge above the flutes. They have also been black oxide bits, perhaps because black oxide is the least expensive coating.
Would love to hear what the machinists and metallurgists out there can add to help in choosing quality drill bits.
Thank you.
In China, unless otherwise indicated, "high speed steel" seems to be "4341" or "4241" meaning 4% tungsten, 2% or 3% molybendum, 4% chromium and 1% vanadium. They generally rely on the titanium nitride coating to make up for the inferiority of the steel alloy relative to M2.
M35 adds 5% cobalt and M42 adds 8% cobalt to the alloy to make bits more suited for drilling in hard metal.
To their credit, the Chinese manufacturers are at least honest about what alloy they use. It's like pulling teeth to get this info from the major brands.
There is also the question about how the bits are made, roll forged, edge ground or fully ground, the latter being the best. One question I have is whether one can visually distinguish between the processes. All bits I know to be roll forged seem to have a raised ridge above the flutes. They have also been black oxide bits, perhaps because black oxide is the least expensive coating.
Would love to hear what the machinists and metallurgists out there can add to help in choosing quality drill bits.
Thank you.