This is a really straightforward method for hanging floating shelves. I use it for hanging mantels as well.
The carcass is made of red oak with a continuous grain at the corners (cut from one board). Unnecessary, but fun. It could be made from oak plywood as well.
The shelf/mantel is hollow except for a few support members spaced appropriately. Also, these members do NOT traverse the full depth of the shelf. This allows the shelf support to be inset into the shelf carcass. Study the photo showing the back view.
The shelf support mechanism can be constructed of 3/4” material typically. I use poplar quite often as it is light and sufficiently strong.
Support arms should be cut 1/4” less than the depth of the opening in the shelf. This allows for easy installation and also the ability to place shims on the self supports in the event the shelf needs to be leveled. Arms are attached using pocket holes.
If a shim is required, use masking tape/blue painters tape to affix the shim.
The beauty of this method is that shelf supports can be constructed and placed on the wall easily by attaching the shelf support mechanism to studs/nailers with appropriate length screws.
This is our shelf…we can do anything we want to with it.
Once the shelf support is installed, slide the shelf on, check for level and adjust as necessary. Note: the shelf support mechanism should not be as long as the opening in the shelf to allow lateral adjustment.
A single screw can hold the shelf to the shelf support by screwing through the shelf bottom into a shelf support arm.
Enjoy creating your floating shelves without being restricted by various floating shelf mechanisms.