Drill Bit for Steel Education

[theoldwizard1]

HOLD ON

You will get info on good and bad drills, and it tells you a lot.

The most probable reason they are not drilling is that they are NOT SHARP. In my experience, I would say most big box brands need to be sharpened out of the box. Don't buy more drills - spend your money on a drill sharpener like Drill Doctor. You will always have sharp drills.

Under 1/4", just buy new drill bits !

 

[vanapplebomb]

I've never had a HSS bit that'll cut anything harder than mild steel. For any kind of hardened steel, I go cobalt.

Depends on the grade of HSS.

M2 is slow going above RHc 40, and poops out at about RHc 50 or so depending on the temper. One exception is on a material like flame hardened grey cast iron. M2 will still blow through that no problem even though it can be RHc 50, or even a bit north of that.

M35 and M42 have more cobalt, which allows you to drill faster in hard(ish) materials, but even M42 is pretty limited in effectiveness above RHc 50. Anything above that is carbide territory.

I almost always use M2 twist drills for general steel work. With coolant, they blow right through moderately hard (RHc 35-40) 4140 ChroMo steel, no problem. I use M42 for center drills, S&D bits, reamers, countersinks, and stuff like that… but all my number, letter, and fractional drills less than 1/2” are M2.