drills 8mm drill bit - Cobalt metal drill bits for drilling hard steel, cast iron, sheet metal & stainless, hardened heavy duty twist drills, 5% cobalt M35 jobber wood masonry

I initially struggled to get success with this drill bit, but turned out to be my fault. Using a 14.4V battery hand drill I could barely make a small indent into a 15mm thick flat wear bar (similar, but not the same as, Hardox 500) with Brinell hardness of HBW=500 +/-10% (= approx. HRC=47-56 Rockwell C scale). These drill bits are certified at Rockwell C=66 so should have no problem in this metal.Turns out my inexperience was to fault - I was trying too high a drill speed, and probably not enough downforce to get it going. I also blunted it by trying hammer action when all else failed (bad + stupid idea). In the end with a bit of trial and error I found a good technique to carefully re-sharpen it on my bench grinder, then slowed the drill speed right down and with firm force to get it going it the drill cuttings started to form and drill bit made it's way through ok, though I stopped several times to sharpen it again until I got a good profile that lasted longer. I think when you hear the squeaking sound you need to add more cutting paste/fluid. I also tested the TTP paste against some old (unused) Castrol magnatec engine oil and the TTP cutting paste definitely lasts considerably longer before squeaking begins.

Bought 4 x Cobalt M35 metric drill bits for metal by TTP HARD drills. 7mm, 7.5mm, 8mm and 10mm. None of these made any more than a slight mark on a high tensile steel bolt. I bought them based on the online video by TTP. An expensive waste of money- Very dissappointed.

Excellent bits they are capable of drilling really hard steee.