How to design a flight case if you want to stack several identical ones on top of one another? Using 4 stackable ball corners (medium or large) and 4 normal ones, is a good start. You can put the 4 stackable ones onto the top corners of your case and the 4 normal ones on the bottom corners. The cases will be easy to stack if you have several identical ones: the normal ball corners on the top case will then slot nicely in the ‘dents’ of the stackable corners on the bottom one.
But practice has shown this is mostly not enough. After all a case is not perfectly ‘straight’ most of the time, meaning that in reality two of these cases on top of each other will still be a bit unsteady, in spite of the theory. A construction with 2 or 3 of these cases will usually not be very stable at all. And if the bottom case has any handles or butterfly latches on the top of it as well, the instability is only going to get worse.
So we at flightcase-brico.com usually recommend to combine stackable ball corners with rubber feet. In practice this means that you put 4 normal ball corners, 4 stackable ball corners and 1 set of rubber feet on every case you want to stack. The feet will make sure the cases can be stacked more stably; the dent in the stackable ball corners that they don’t bump into the normal ball corners that are stacked on top of them.
We consider this a general rule which we wanted to give you as a nice tip.