Sounds like you are installing them right. The hacksaw blade may be making the slots a little bigger than ideal, but I don''t think that would cause them to fail at the hinge line.

It is pretty well accepted these days that a CA hinge will fail at the hinge line from overstressing caused by the very high deflections and constant surface movement of 3D flight, OR from high vibration levels, such as in a twin or when using a gas engine.

Could one of those be your problem?

Jim