Bookcase Plinth

I'm looking at a bookcase design that has a platform constructed out of 2x4's, which is shimmed, and then the bookcase rests on top. The trim hides the plinth.
I'm not convinced of the utility of shimming the hidden plinth as opposed to just shimming the bookcase itself, then attaching the trim. If the platform is smaller than the perimeter of the bookcase, then the entire weight is supported by the bottom shelf, which isn't good. It really must be exactly the same dimensions as the bottom of the bookshelf and thus seems to add extra work without benefit.
Am I missing a potential benefit?
Thanks
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Greg Esres wrote:

It's easier to level the platform first. Typically only the front of the plinth is recessed. If the sides are supported by the bottom it'll be OK. Phil Brown
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Phil Brown wrote:
<<If the sides are supported by the bottom it'll be OK. >>
Couple hundred pounds of books supported by one shelf?
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Greg Esres wrote:

I like to do this when I'm building multiple unit built-ins and window seats. I can create a level base to install the boxes on, ala cabinet-style. My bases are strips of cabinet grade ply instead of 2x's, as I find the plywood more stable. I've never had to buy extra plywood to build the base, I always seem to have suitable leftovers, especially since the face veneer species doesn't really matter.
My ends line up with the outside uprights, the bottom shelf doesn't support the whole unit.
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Barry wrote: <<My ends line up with the outside uprights, the bottom shelf doesn't support the whole unit. >>
So if you were building multiple units, you would have a plinth whose structure mirrored the sides of the various units. In other words, if you had 3 book case units, you would have one plinth that supported all three, and you would have some cross members to lie under each of the cases sides?
I'd kinda be worried that any width deviation of the book cases would end up with the last case hanging off the edge. :-(
Thanks
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Greg Esres wrote:

Yeah.
and you would have some cross members to lie under each of

No. The long stringers carry the sides, as well as the shelf. There are a few crossmembers to prevent bowing.

Not if you're reasonably careful.
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The load of a bookcase rests on the 2(?) sides. I like to tie the two sides together with an apron under the bottom shelf. An easy way to stabilize this plinth is to create a four sided box. I like to cut the bottom of the sides at a slight angle so that the bookcase has to lean back against the wall, this causes the plinth box to have a different front and back . I still like to pin the top of the bookcase to the wall by some method, but a slight lean helps to compensate for carpet tack strip and load dynamics. ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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DanG wrote: <<I like to cut the bottom of the sides at a slight angle so that the bookcase has to lean back against the wall, this causes the plinth box to have a different front and back .

Why not just shim it that way?
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