Tip: Drilling Hardened Steel With Masonry Bits

This was actually a tip that I got from a comment on my “Making A Knife” video that I dismissed as something that wouldn’t work. I normally try to have a more open mind, but thought that there’s no way you could get a masonry bit sharp enough to drill into hardened steel. Well, I stand corrected and it’s a good example of how we can discount an idea based on what we think is correct, when it’s always better to take the time and try it first.

The bits I’m using for the test:

the two masonry bits

One is a regular, cheap masonry bit that I’m pretty sure I’ve never used. The second is a high quality SDS bit that I cut the thickened shank off of to use in a regular drill. The SDS bit has been used many times and is very dull.

To do the sharpening, I have a 7″ tile cutting blade set up in my table saw:

the tile cutting blade
tile cutting blade in table saw

This blade is not ideal for sharpening carbide, as the diamond particles are a bit too large to do a good job. It’s all that I have right now and I figured it will be good enough for a quick test.
Since I would like to make a circular saw sharpening jig at some time in the future, I will be getting a proper grinding wheel for that purpose, and that can be used for this as well.

Here’s a close up of the tip after “sharpening”. Not perfect, but it didn’t have any problem drilling through the 1/4″ thick hardened steel chisel I used for the test:

close up of the drill bit tip
the holes drilled into the chisel

The second, unfinished hole is from the SDS bit. I stopped after it was clear that it wasn’t going to finish and I believe I could have done a better job of sharpening that one. Still, it did make it more than half way through the chisel.

More or less just to verify the test, I drilled into a wrench:

the hole drilled into the wrench

The thinner bit that I used made it three-quarters of the way through the wrench easily before losing its edge.

I made a video of the test:

In conclusion I’ll say that it definitely works, and possibly a lot better than demonstrated here if the right grinding wheel is used to get a cleaner cutting edge. Also starting with a new, unused bit will make a difference. The bits I used were worn out and used in a hammer drill, which would make the carbide more prone to breaking.