Flooring Tile - Cut Square Hole in Ceramic Tile

This one has me stumped so I'll probably be searching for a tile store to do the cut for me but I wanted to ask here for advise.

I have one tile in a bathroom floor that needs a square cut out of it for a floor vent. 18" tile, the hole is about 5x10". So I made my marks and took it to the wet saw (cheap HD version) to make my plunge cuts. First two tiles cracked before I could complete one cut. So I chalked it up to a cheap saw/blade and moved to the grinder. I went and picked up a brand new diamond blade, made my marks and began cutting. I had more luck, but five tiles later still could not complete the hole. They all kept breaking.

For some more detail, I would cut the square outline, then an "X" in the middle. On both sides. Sometimes the tile would break during the "X" cut, sometimes on one side, sometimes the other...no rhyme or reason. I tried with the tile sitting flat on my workbench or sitting on a 2x4 frame so the middle was open underneath. No change.

Any tips for doing this cut?

I like to drill pilot holes in the corners of the cut first. This prevents stress fractures.

Try drilling the holes first, then use your wet saw or rotozip type tool.

I usually make these cuts with my 4" grinder and diamond blade.
and once and a while with the wet saw which is harder but can be done.
sounds to me like your tile is brittle.

Two shops that do cut tile refused to do an inner cut like this. I found a shop that has a water jet so I dropped off a tile there. Hopefully that'll work ok.

Still frustrated I couldn't get it done.

water jets are awesome. i am sure it will work

Tile broke for the water jet shop as well (they tried two tiles, broke in the same place.) Now I don't feel so inadequate. Just have to figure out what plan B is. Maybe epoxy what they ended up with, or do "U" cut and create filler piece for fourth side, I don't know. Should be a fun weekend.

you might just try letting them waterjet it and where it breaks super glue it back together.
I know it isn't the best way, but you might not even see the small crack where it broke naturally one done.