still questions about drilling in hardened steel

[Cushing H.]

Glad you got holes in your blade.

Interesting experience. Went back to my bench to complete the rest of the blades, and noticed that there was steel melted into the flute of the drill bit. That bit would not cut again, and was toast after 2 holes (and a time delay after). Seems to me that doing this relies more than a little bit on heat. Run the bit until the steel below heats up and softens and the bit starts cutting. dont stop (keep the heat on) until the hole is through. I then did my best to wipe crud off of the tip with a wet paper towel, shift to the next hole as fast as reasonable. rinse and repeat. Got six holes done with that second bit. Last hole cut almost as well as the first. I will lay odds that now, with a time delay, the steel in the drill bit tip has hardened, and that second bit is now useless (would test - but I do not have any more blades to drill ). The flashing on the back of the holes was easily removed/taken down with a file ... so it does appear the steel there was locally annealed.

If this is the case ... that then makes sense of what others have said: dont use too high a drill speed (will burn the bit), not too slow (wont generate enough heat?), medium pressure, etc. seems to make sense in that light.....

 

[Natlek]

C Cushing H.
Something is wrong with that carbide drill bits , most likely not sharpened properly .Good carbide dril bits will drill hole in that hardened steel easy like razor sharp HSS-E dril bits will drill in wood , trust me .

 

[John hanway]

I use a dremel with aluminum oxide pointy bit till halfway then small medium large normal drill bits only because dremel bit wears out pretty fast but there cheap

 

[tkroenlein]

I use carbide twist drills (just like regular bit helix) running highest speed on drill press, 3600rpm I think, flooded in coolant and fed slow enough to produce "swarf." That is fine dust mixed in coolant. It seems to me that any time I feed fast enough to get a chip or curl, a shattered bit is soon to follow.