First, hacksaw blades are not easy to drill through. I searched and searched and burned up a handful of various drill bits before I found one that could consistently drill through the blades I use (Stanley brand). I finally arrived at Dewalt Split Point Titanium Coated bits. Other titanium bits couldn't even make a depression in the metal, the split point is the only variable so I assume it made the difference. I also tried cobalt bits with no success. This was all done on a drill press and oil lubrication. After about $25 in destroyed drill bits I was beginning to think it couldn't be done with conventional tools. So ya, long story short... blades are hard to drill through.
The post is really old (and it was about tension wrenches, not drilling per se), but thought that I'd pass along a method to drill through very hard steel easily, especially thin and hard steel. With a propane torch one could anneal (take to red heat then set it aside to cool down own its own) the whole thing, but the assumption here is that one likes the heat treatment already in the steel and one wants to preserve it. The key is to anneal the metal in just the area where the hole needs to go. Take a bolt with the head hacksawed off and ground smooth, or some other round piece of metal the size of the hole to drill. Chuck it up in a drill press and set the belt to high RPMs.
Turn it on and press down. Don't stall the motor, just press down. The spinning round metal gets hot and will heat up the thin metal very nicely in just that area. It only takes a few seconds. The area will be discolored--that is a good thing.
Then chuck up the drill bit, set the belt for the right speed, center punch the steel, and the bit goes right through. A person can put on a drop of oil (basically any sort of oil will help) on the spot to drill as well. Showing it on a hacksaw blade here, but have used it before on industrial steel-cutting bandsaw blades.
