I've never used a spring joint for panels. I'm wondering if it is worth trying on my next panel glue ups that I'll be doing.
I can see a nice advantage of a slightly convex (gaps at the ends rather than the center) as it would seem to provide a tight joint with less clamps. However, it seems more effective way of doing this is with cauls.
I'm struggling to understand any advantage of the concave (gap in the middle). I've seen the indication of humidity expansion/contraction and such. I'm not following this reasoning though. Once the glue dries without a gap, it seems if there is uneven wood expansion/contraction would be the same issue if there was no spring joint used. I'm just not following the thinking and I'm curious if there are any studies done or case studies. It seems this is considered the more common spring joint. Or maybe I just have come across more of these on the internet.
I do wonder if creating a joint that is consistently slightly convex may be easier than trying to create a flat joint (which is my normal attempts). My "flat" joints will often end up either slightly convex or concave in areas. Granted these are small. But I have to pay attention to where these are to clamp it such that they are removed. This is the one thing that has my interest in these. But then I debate with myself if cauls are really the better answer.
Then I wonder if simply putting the joints together and running them over the jointer is the simpler and best method. I'm not that great with a hand plane. If I were I could definitely see just making a pass or two with a hand plane.
My conclusion that I haven't tested is to clamp my boards with the joints matching then run them over my jointer. The make cauls to help minimize the number of clamps needed.
I'm interested in your experience and thoughts. I have come up with things like this before and when I tried them, I quickly realize I'm struggling to get it all to work.