minifhncc wrote:So, in what applications must one balance a stack?
As I understand it, there are several reasons for balancing the stack.
One reason is to prevent an overlifting attack. Short drivers allow the short key pins to be lifted all the way out of the plug, so that they no longer prevent the plug from turning. In some cylinders, long drivers paired with long key pins could result in the cover of the pin chambers coming off, releasing springs and pins from the cylinder. Some locks use set screws to prevent this.
Some manufacturers recommend balancing in order to prevent more sophisticated attacks involving analysis of the pin stack, especially the weight.
Also, short drivers paired with very short key pins will sometimes result in both pins sitting completely in the plug, below the shear line. Not only does this not prevent the plug from turning, but it allows the springs to cross the shear line, sometime resulting damaged springs and cylinders, and a nasty jam of the plug. If you are pinning Schlage-type cylinders for picking practice and choose to use zero pins, be sure to use long drivers to prevent this frustrating problem.