Drilling will have a lot to do with cracking. You must have 1 3/16" from the edge of the hole to the pin and the MB(i believe with some companies) in order to be covered by warranty. Some customers come in and have specific layouts that compromise the integrity of the ball and void the warranty. I make sure to remind them of what the layout will do to the warranty. Also chipping the pin deep in the hole may compromise the integrity as well. Which is why companies ask to drill out the pin or mb(if mb is drilled in) if a gripping or weight hole is within that area.
Thin shelled balls, gluing of grips and slug, and shell hardness will make cracking more likely. The harder the ball the more likely the ball is to chip and crack, which is why plastics and weaker balls chip and crack. It is also key to glue the grips and slug to the cover and not the filler. With thinner shells, its a little harder to do.
One of the big reasons i throw Storm/Roto is I like the shell thickness and the "marked" MB instead of drilled like per say Ebonite, C300, and some Brunswick Asyms. That doesnt mean that they roll any better than any other company but it's definitely a plus in my book. I've seen some C300 pieces crack because of the drilled thumb being to close to the MB. My Total NV cracked from the MB all the way round to the fingers. It just raises your chances.
Laying balls on the floor during down time can increase you chances if you have a concrete pad under your carpet or hardwood. The concrete is quite a bit colder than the house temp, which can leave you scratching your head.
Just somethings to consider.
