Double glueing involves that after a joint has been glued and cured we apply a second application of glue in the corners to create a fillet. The fillet is made of the same glue.
Zor,
This is what you posted, and I didn't see anything after all about what I'd call 'double glueing', so my first post stands. Your technique is better termed a 'glue fillet'. Folks should be aware that glue of itself doesn't make a strong medium, especially when stretched to '5x'. Were that so, we could build the entire airframe from glue.
Let's not lose sight of the big picture, that there's a huge variety of glues available, and nearly as many techniques as builders. My oldest brother was a part-time luthier (builder of stringed instruments, he repaired guitars for rockers, a few big time), and he used horse-hide glue among others like Titebond. The horse-hide was the strongest by far, over 3,000 psi til failure IIRC, but I haven't seen any in over a decade.
For those who don't know, here's an image of a glue factory: