On Nov 14, 4:17 pm, "dean" wrote:
Ok I know i can drill a whole load of little holes in a circle and then
knock it out, but is there such a thing as a 4" drill bit that will do
this more easily?

Drilling holes around the circumference is the easy way to do it. You
don't need additional tools and expenditures and it's almost as quick
as a core bit. If you have a 4.5" angle grinder with a diamond blade
you can clean up the hole to make it rounder. It'll make more dust
that you'd believe, but it will do it just fine.

R