Is it drillers fault, that almost every ball that he drills will crack about finger holes?

Does he bevel the edges slightly before installing grips? Also putting the glue down further below the coverstock line will help. As The glue dries it won't flash the coverstock it will flash the core material.
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Billy Ray
Track Pro Staff
Owner Rays Pro Shop
At The Playdium
"Let Us Help You Become More Competitive"

I use a brush bottle of super glue and only apply a thin film all the way around the holes, about 1/2" below the surface.  It's probably not a total of over one drop.  And when you use a drop the glue spreads out and up when the grip is pressed against the side of the hole, bringing the glue all the way to the surface frequently.  I also bevel the hole and don't have any problem with finger holes cracking on balls I drill.  --  JohnP

It is only necessary to glue the finger grips on two sides. That is all it takes to hold the grips plus it makes it easy to remove the grips when replacing them. I use Loctite Super Glue Gel and put the smallest drop I can on two sides and I put the glue down in the filler area and not on the cover stock at the top. By doing it this way, I have never had a cracking problem around the holes caused by the glue and I have never had a grip come loose either when putting only a tiny drop of glue on 2 sides of the grip.
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"Whenever I feel the urge to exercise I lie down until the feeling passes away."

Brick

Just to add a couple of things to what has already been posted. If the drill bits become dull from a lot of drilling, which will cause the balls to crack due to the heat generated while drilling a ball. And some drillers do not use enough lateral pitch on both finger holes to keep the holes from coming together at the bottom of the hole. This will cause a crack sooner or later.

jodyk24