Hope this is the right place.
I have a cnc machine with an adjustable bosch router. I need to cut a couple of 1 1/2 inch holes in two 1/4inch thick bathroom tiles to take a shower mixer. Unfortunately I only have two tiles left of the right colour so can't afford a mistake. I have done some experimenting on similar, different coloured, tiles with various types of cutter. The glass drills seem to cut the surface but any metal cutters glow red at the slightest provocation.
Is there anything I can put in to grind through this material? Time is no problem as I can set it to cut in the smallest steps and leave it, although any lubrication would have to be by hand.