Now these: Stackable Ball Corners
I've chosen these because to me they seemed the natural ending for the corners, also the are very strong and once fitted they are attached not to the Ls but to the alu sheets making the structure stouter in my opinion.
Because the "Balls" have rounded ends and our case has sharp corners we need to file or "munch" with pliers a few mm in order for the Balls to seat properly. The result will look like this:
apply a ton of sealant (remember, this is the bottom, we want it to be waterproof) here:
push it in place and be ready with the drill. don’t worry about the sealant coming out, it means the inside is full: good.
Now the tricky bit is to make sure all 3 sides of the corner ball are siting flat against the case otherwise we will have problems later bridging those gaps, you can use a hammer and bang right in the middle of the corner ball to sit it properly.
Rivets: I have noticed that my 7mm rivets are just long enough to catch the alu sheet, I didn’t have any others at home but I would have preferred to use some longer ones, 10mm probably but not longer than that otherwise they will bother us on the inside of the case once finished.
Now with your finger, wear a latex glove if you can, clean the surplus of sealant pushing it into the gaps around the ball corners, at the end it will look like this, ( once dry we will cut the surplus neatly):
At this point I left the cases a couple of days for them to dry because I didn’t want to get into more sealant and I didn’t want to damage the seals themselves.
As info: working at a temperature of 13/14 degrees it took 2 days before I could cut the excess of sealant neatly but in a warmer and drier place (I live by a river close to the Venice lagoon... quite humid here...) it may have taken less time.
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Then found the proper alu profile (see picture), I added an edge to the case
This step can be skipped as it doesn’t make the case more
waterproof or stronger, I done it just because I though it would have been nice
to have a smooth edge. If you think u want it as well u will have to find the
correct alu profile before starting the sawing process and make your calculation
as this should not overlap the Ls, you will have to leave some clearance at the
top for the new profile as shown in the pic below.
I didn’t cut the profile in four pieces but I made 3 deep cut half way through and then bend it around the edge of the box, like this: