Box joints for hanging cabinet

Here's Norm making a medicine cabinet using box joints. You'll need the required belt sander and brad nailer.

I don't see why you couldn't use a brad or a nail or a screw in the box joint. I've done it with pegs in both box and dovetail joints in drawers when I was concerned about wear over years of use. There are so many ways to join wood in an application like this and so many variations that could be applied to each that one could spend a lifetime trying them all out (if you work as slowly as I do, anyway). Here is an old-school way of doing pegged box joints although using rectangular ebony pegs is kind of out there if you are looking for simple:

Done properly is is very pretty, you must admit.

They are and aren't. If you glue a couple of pieces of wood together and then bust the joint, it will fail in the wood. However if you take the same two pieces, hang them by a hole in one and hang a weight on the other, so the glue is loaded in shear, you may find that after a while they have come apart. It's called "creep"--slow movement of a joint loaded in shear under continuous stress.

A tightly fitting, correctly glued box joint should be stronger than the wood around it. I don't see the necessity of additional reinforcement.

Assuming that the joint is fitted well and the glue involved is guaranteed to never creep under constant load then reinforcement is not needed.

I don't see the necessity of security blankets but if it makes the OP feel better about it, what is the harm? I back my computers up to three different destinations and keep copies of my data in a bank vault. Necessary? Maybe not but it lets me sleep better at night.

Even if it creeps- how long would it take for 12 inches of 3/4" box joints on a 3/4" stock to creep enough that you can even see a gap? Considering the number of faces glued to each other, I suspect that would take centuries.

This cabinet is going above a toilet. Those glue joints may need to support multiple rolls of toilet paper. If the OP uses 2-ply paper, there will be substantial sheer force on those joints. The creep might be an issue in a relatively short amount of time, maybe a couple of eons at most. ;-)

It's hard to be sure that a cross-grain joint (box joint) won't be stressed, internally, by wood movement in addition to a constant load stress. That makes it a little less certain than a dovetail (where some wood could do brittle breakage), and a lot less certain than a dado (where a 12" shelf has a half inch under its dado socket) that must make a 12" long check that splits 6 square inches of wood faces.

For what it's worth, old box joints do NOT stand up; hide glue gets eaten by fungus, in about 150 years...

I doubt he is building how I do. :~)

I think pegging of the joint is best described in your last sentence. I think for any other reason may be overkill. There is a LOT of glue surface in a box joint, triple, IIRC.

I don't use glue that is guaranteed not to creep. In 40 years of serious woodworking I have never had an issue with creep. I only see it when gluing 2 pieces of wood that expand in different directions. The joint is still rock solid but now, 10 year, later I can feel the joint.

Glue creep is IMHO something that happens but is not an issue for an application like the OP is concerned about. Kinda falls under the assumption that clamping too tightly will starve a joint of glue. Again nothing I have ever witnessed. The strongest glue line is a thin glue line.

Agreed but one could have 5 different destinations and be even safer. You learn what is necessary and what is not with experience.

I would be more concerned with the 2 ply paper sheer resistance to a middle finger poking through. ;~)