I had to drill several 3/8" holes into very hard concrete. I purchased a Bosch LBH008 drill bit, but since I hadn't received it, I bought a cheaper $3.60 Makita drill bit that drills incredibly slow. Not only that, but the whole building can hear it since it's the very hard concrete used for the actual building (it's for a fence).
So today I received the new bit. Is it worth switching to this new bit or will it be as slow as the $3 bit I bought three days ago?
I'm using a Craftsman hammer drill.
Best Answer
Neither bit will do well in a standard drill. You need hammer action to chop through concrete with any sort of speed. A hammer drill (conventional drill with hammer action) will work for a few holes with some patience. If you need to bore many holes or to work quickly, a rotary hammer is a must, and they only accept SDS bits with the larger, slotted shaft base.
That said, the bit itself isn't terribly important with respect to shape. Even worn hammer bits do well if the carbide cutting blades are still attached. They fail when the blades break free of the bit shaft at the weld. At that point the metal in the shaft mushrooms over and you're done.
In short, either bit will do poorly or well depending on the tool that's driving it, and it's just a matter of durability. To get maximum life, spin fast and push slow. Allow cooldown after every few inches of cut.
Since you're using a relatively light-duty hammerdrill, I suggest purchasing a 3/16" bit and start each hole with that. 3/8" is rather large without a rotary hammer and you'll be at it for quite a while.