Lobster wrote:
I'm now tiling the ceiling of my shower cubicle, into which there will
be a shower fan/light inset, so a 4" diameter hole is needed through the
tiles. This will affect 2 tiles only, and I've already cut out two
half-moons from these using a hand tile-saw but have yet to attach these
two to the ceiling. These are standard ceramic tiles, ~6mm thick.

Unfortunately however, the hole's a bit tight for the fan, so I need to
enlarge the diameter by 1 or 2 mm - the sort of task I'd normally do
using a file or rasp were I working in wood or metal. But what would be
a good way of abrading a ceramic tile without busting it? (It took a
long time to saw the hole, so I'd rather not have to do it again!)

You could always see how much meat there is in the fan housing, and see
if it could deal with a trim.