I saw those shelf mounts as well and decided to add them to a cabinet I made for my fiance. I varied the design a little bit, but the concept’s the same. ๐
I made a .pdf that shows the dimensions I used to make mine.
In the first pic, I used a dovetail saw to cut the four segments, then chiseled the waste away at an angle. I used my router plane to channel out the slots for them to sit in the sides. After I fit the first two in, (the second pic) I realized the shelf wouldn’t sit in there without a better recess, so I chiseled across the piece to give room for the shelf to sit. After I did about six of those like that, I decided to break out my scroll saw and made quick work of the rest of them (24 in all).
The third pic shows the top half of the cabinet. I hadn’t made the lower half at this point. Now, I keep forgetting to take pics of the completed project. Maybe one day I will ๐
Hope this helps ๐