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Discussion Starter #1 (Edited)
Here is the basic idea of a bookcase I'm looking to make, pardon my drawing skills.
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Let me be the first to say that the design is both weird and deserving of explanation. Each of the 5 shelves is solely attached to the frame of the bookcase by being cantilevered off the back wall of the bookcase, and each shelf is narrower on each side than the width of the bookcase. Those arrows in my drawing attempt to depict space between a shelf's edge, on either side, and the side walls of a bookcase.

Crazy design, right? But with some "method to my madness" it is my hope to be able to slide the following table, (albeit one I make, not this exact one) that itself converts into a bookcase, inside the bookcase in the above picture when the table is stored and not being used.

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Each of the shelves that comprise the table in its smallest footprint configuration on the right of the above picture would slide, of course with no contents on the (table's) shelves, into the bookcase--whose (bookcase) shelves may very well have contents. The table's shelves would sit immediately under each bookcase's shelves.

Ok..sure, the table legs are somewhat long, making for a deep bookcase--but such issues can be addressed so forget them for now.

At this point perhaps, if nothing else you appreciate the motivation behind the design of the cantilevered shelves bookcase with clearance on each shelf's sides in that the table, in its upright position, slides into the bookcase and into those gaps on either side of the bookcase's shelves.

With this background, my focus turns to how to best make the cantilevered bookcase shelves super strong. My idea is to buy two pieces of 3/8" ply for making a 3/4" thick overall bookcase. In one piece of 3/8" plywood I will cut slits where each bookcase shelf's center of height is, and stick one leg of metal angle brackets like these (forget the screws that come with the brackets) through the slit.
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I'd router out half the thickness of these brackets into the back of 3/8" piece to which I'd glue them. I'm thinking of using original Gorilla Glue to do this. Any thoughts.

The other piece of 3/8" plywood, also routed to half the bracket's thickness, would be glued to the backside of the already used 3/8" plywood panel. This "sandwich" would form the back wall of the bookcase. The bookcase's side panels would be 3/4" plywood.

With the installation of these metal brackets I could make bookshelves using the same sandwiching type method I used to attach the brackets, where the two 3/8" panels that make a shelf are the metaphorical "bread," and the portion of the metal bracket that is perpendicular to the back of the bookcase, the "meat," no differently, in principle, to how I made the back wall of the bookcase as described prior.

What are your thoughts on this design? I want shelves that are as strong as if those shelves attached to the sides of the bookcase like an ordinary bookcase.

Thanks in advance.
 

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First thing I would do is build a proof of concept - namely a one shelf experiment to see if the brackets will support the weight and not bow or or break the 3/8" sandwich back. Second I'd think about ways to keep the sides in place namely top and bottom support with leveling feet. Also the glued joint between back and sides strikes me as a weak joint. Perhaps a dado for the back wall into the sides.

Russ
 
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Discussion Starter #3
First thing I would do is build a proof of concept - namely a one shelf experiment to see if the brackets will support the weight and not bow or or break the 3/8" sandwich back. Second I'd think about ways to keep the sides in place namely top and bottom support with leveling feet. Also the glued joint between back and sides strikes me as a weak joint. Perhaps a dado for the back wall into the sides.

Russ
Thanks @Geeze. You've given me thought about using original Gorilla glue only in the areas that join metal bracket to wood, and wood glue for all other areas to bind my "wood sandwich," as well as using wood screws to "screw and glue" my wood sandwich.

And yeah, test first on scrap: smart.

Certainly, as it was always my intention, the side walls of the bookcase will be joined to the back wall, at minimum, with both "screw and glue," if not, additionally, some of the joinery joints (e.g. dado) you mention.
 

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Original Gorilla Glue is a brand of polyurethane glue. It is no different than other polyurethane glues. I use it on wood and metal, but only to glue small brass pen tubes into their holes in pen blanks. For that one purpose only, it is a good match for me.

Polyurethane glue is a strong adhesive, but not as strong as other glues. In addition, it foams. The foaming action can create clean-up issues. Even though it fills gaps, the foamed glue is mostly air and is not strong.

I think your best choice would be a good quality epoxy. In case it matters, I have been using G/Flex from West Systems. It was recommended to me by someone here. The advice was good - it has worked well for me.

If you want to try a one-part glue on a smooth joint (no big gaps) of mixed materials, consider Clear Gorilla Glue, which is a silane-based glue and unlike any other glue I have seen. It is not polyurethane and it does not foam. I think of it as a one-part epoxy. I continue to use it (because I paid for it, right?). Frankly, based on my experience, a good epoxy holds better.
 

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Discussion Starter #5
First thing I would do is build a proof of concept - namely a one shelf experiment to see if the brackets will support the weight and not bow or or break the 3/8" sandwich back. Second I'd think about ways to keep the sides in place namely top and bottom support with leveling feet. Also the glued joint between back and sides strikes me as a weak joint. Perhaps a dado for the back wall into the sides.

Russ
@Geeze: you've given me another thought:

Here's design two of the bookcase, again: pardon my lack of drawing skills:

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I've introduced sides to each shelf that not only aid in the strength of the shelf they connect with, but serve to confine the contents of a shelf, which may contain top heavy items like books, from occupying the space on either side of the shelf that would prevent the table, in its shelf position, from easily being removed from or inserted into the bookcase.

Thanks for making me thing more about this with your commentary.
 

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Discussion Starter #6 (Edited)
Original Gorilla Glue is a brand of polyurethane glue. It is no different than other polyurethane glues. I use it on wood and metal, but only to glue small brass pen tubes into their holes in pen blanks. For that one purpose only, it is a good match for me.

Polyurethane glue is a strong adhesive, but not as strong as other glues. In addition, it foams. The foaming action can create clean-up issues. Even though it fills gaps, the foamed glue is mostly air and is not strong.

I think your best choice would be a good quality epoxy. In case it matters, I have been using G/Flex from West Systems. It was recommended to me by someone here. The advice was good - it has worked well for me.

If you want to try a one-part glue on a smooth joint (no big gaps) of mixed materials, consider Clear Gorilla Glue, which is a silane-based glue and unlike any other glue I have seen. It is not polyurethane and it does not foam. I think of it as a one-part epoxy. I continue to use it (because I paid for it, right?). Frankly, based on my experience, a good epoxy holds better.
Excellent thoughts @Tool Agnostic . As your namesake may imply, you're not married to any particular tool, just the best one for the job.

I too can concur with the greater adhesion properties of epoxy. I recently epoxied these furniture insert nuts into wood and their held their better than any other gluing method I could find. Here's the build: Making T tracks directly into wood

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Epoxy it is!!! Thanks!
 

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Discussion Starter #7
Oh, and yes..I realize the top (shelf) of the bookcase can span the entire width of the bookcase, as the table, in its bookshelf configuration will in its entirety sit below that height. I drew it cantilevered though to better detail the design intention for all the remaining closer-to-the-ground shelves.....:)
 
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