This seems like a stupid question, but I cannot figure it out ...
I have a couple of masonry hole saws (carbide tips) that I am using to drill holes through a cinderblock foundation wall for various purposes. I have a mandrel for the hole saws. It accepts a 1/4" pilot bit.
But since I'm using it for masonry, the pilot bit needs to be a masonry bit. So I bought a 1/4" masonry bit. But guess what ? The shank of masonry bits is usually smaller than the carbide tip at the end of the thing that does the actual cutting. So my 1/4" masonry bit drills a 1/4" hole, because the carbide tip is 1/4" wide, but the shank is a bit less.
This means that when I put it into the 1/4" hole in the mandrel, it is actually off-center. Worse, it's at an angle, because of the way the set-screw pushes on the side of the shank. The result is that the carbide tip of the pilot bit wobbles. For the 10" bit I'm using (to get through to the other side of the cinderblock) the wobble is quite bad.
Question: how do I source a masonry bit that has a round shank of exactly 1/4" diameter ? This is not something that is spec'd. Am I missing something ? This seems like a silly problem that many people have to deal with.