On June 28 2006, " wrote:

Never used such a large core drill, but with a 45mm I always go
striaght in with guide bit and core as one. I can't see why you wanted
to pilot the guide bit right through first.

The plan was that I could then cut from either side if one prooved too
difficult (just above a shelf) as it was a big lump of brick flew out of
the outside so I had nothing left there to guide the drill core anyway.

I have used plenty of metal cutting hole saws up to 75mm and know that
the guide drill is paramount to cutting a clean hole in metal but this
is my first attempt at brick cutting.