Tap hole in bandsaw cast iron table

[Kevin Beitz]

Make sure the drills turning clockwise looking down....

[Ole Anderson]

If that is the drill bit you are using, it is the wrong type of drill bit. That type is designed for wood. Try to find bits that look like this:
Attachment 416159

Actually the Irwin Turbomax is designed for metal cutting in much the way Dewalt Pilot Point bits are. Not to be confused with brad point bits which are designed specifically for wood. I have found the pilot point bits work rather well in most metals.

[Osvaldo Cristo]

I am not a Metallurgist but I guess there is a wide variation on cast iron.

My limited experience on the subject had found one very easy to drill and one completely impossible for mere mortals...

[Tom M King]

Sometimes even in the same casting, there can be relatively soft areas, and harder than it seems like possible areas, depending on the care in the whole casting process. The engine block I had to rethread those large holes is was some very nice cast iron by (or for) John Deere. Google "drilling hard cast iron", and you'll find some interesting stuff. There are special drill bits made for drilling really hard cast iron, with designs like three carbide flutes, and an unusual looking grind. I just figure that if a Cobalt bit won't do it, that it's over my head.

[Jim Andrew]

Most of the steel used is recycled, and sometimes, old ball bearings get dumped in with other steel. I bought some 4" channel iron, and drilled holes in it, and found a couple holes where it broke my 1/2" drill bits. Started with 1/4", then 3/8" and finished with the 1/2".