We install hundreds of shower doors every month, and most of the time the installation process goes smoothly. We are in and out and you are able to use your new glass enclosure after a short wait for silicone to cure. On rare occasions, we run into the issue of tile cracking during installation. So yes, it does happen, but not often at all, and there are things you can do or watch for to help prevent this.
The main reason for a tile to chip or crack is because it was installed improperly to begin with. If the tile does not have a solid backing of mortar/thin-set and there are air pockets or voids, it can crack when we are putting pressure while drilling. Be sure your contractor (or you if you’re a DIYer!) takes their time and utilizes the proper backing and mudding, especially along the wall where the door will be hinged, or anywhere the glass will be secured.
Also, some tiles and solid surfaces are stronger and harder while other material can be very fragile. We have years of experience though and usually have no problems drilling into any material you decide to use as long as it was installed properly. We will even install on glass tiles (although it is not recommended). The issue is not necessarily from the drilling aspect, but the pressure and force that are applied at the hinges and the fact that we need to secure the door snugly to carry the weight of an 80-lb door.
If you are still early enough in the tile selection and design process, may we suggest a solution that both looks great visually and will make your shower door installation significantly easier. Choose a smooth/flat/solid material as an inset border where the glass will attach to the wall. This works well if you want to use glass tiles, stone, or other materials with a lot of texture. The shower shown here used a border because of the uneven texture of the stone and the surface not being smooth, but this technique can be used for glass tile as well.
If a tile does happen to crack or break during installation, we will immediately stop the install and notify you of the problem so you can have it fixed, and then we will finish the installation after it has been replaced and the mortar has had time to completely dry. I would like to reiterate, tiles do not crack often — otherwise we would not be in the business of installing shower doors and drilling into tile daily. But it can and will happen from time to time, so it is better to address the reasons it could happen and the steps we will take if it does happen.