Dadoes in both sides of 3/4" ply?

We still haven't settled on our book storage plans. Now I'm considering a design that would involve shelves on both sides of a wide cabinet divided in the middle, but not in line with each other. The cabinet would be 54" high by 48" wide, with a vertical divider a little off-center. To one side of the divider there would be 4 shelf spaces each 12" high. On the other side would be 3 shelf spaces, each 18" high. (all numbers approximate, I know the thickness of the wood will change the exact dimensions). The dadoes on opposite sides of the divider would then be about six inches apart.
All shelves would be fixed. There would be a face frame, and a back. I'm wondering if I should simply make the cabinet as two separate boxes, joining them together after both are assembled. That would give me a double-thickness center divider, but there would be a 1x2 covering the seam anyway. This idea appeals to me because I think it will be easier to handle two smaller, simpler units than one large one. But if do decide to make the cabinet as a single unit, is it OK to make dadoes in both sides of the center divider, as long as none of them are in line with each other?
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On 12/11/12 9:26 PM, Greg Guarino wrote:

Dadoes on both sides of a sheet of plywood would be fine.
However, if it's easier to build two cases, do it. It's not that much more material and there's nothing wrong with it, if the design calls for a center divider. IMO a bookcase that is wider than it is tall looks odd and.... sideways.... so a divider is nice, esthetically.
I'm starting a build-in bookcase project that will be 64" wide x floor to ceiling. I'm breaking it up into two 32" wide cases for two reasons-- sheet goods are 48" and who in their right mind would try to build a single case that big. :-)
--

-MIKE-

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On 12/11/2012 10:59 PM, -MIKE- wrote:

My "design" (more of a half-assed idea so far) was based on two factors: the size and the weight of the books to be stored. These bookshelves will hold books mostly, rather than the usual bric-a-brac. The spaces available are 4' wide, but I don't feel quite right about shelves 48" long. Plus, some of the books are very tall, but most are not. Thus I'll need some tall shelf spaces and some less so.
I was originally going to make the lowest shelf tall and the rest shorter, but if I need a divider anyway, I think it will add some visual interest to break it up the way I described.
IMO a bookcase that is wider than it is tall looks odd

These bookcases will actually sit atop a set of existing cubbyhole units that span a whole wall. The two new bookcases will be placed at either end, with a TV in the middle. Assuming all goes well (and I live long enough, given my less-than-efficient woodworking methods) I may complete a faux built-in with a "bridge" over the TV between the two units. Anticipating the obvious question, yes, I will be anchoring the units into the wall as well.
That is, until the plan changes entirely. We'll see.
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"Greg Guarino" wrote:

---------------------------------------------------------------- No problem structurally; however, you are going to be busier than a one armed paper hanger in a wind storm trying to get everything aligned before your adhesive fires.
You are going to want the longest open time adhesive you can find.
I'd use epoxy with a slow hardener which will give you about 30 minutes open time at 75F.
A good helper will be a big help.
Have fun.
Lew
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On 12/12/2012 2:16 AM, Lew Hodgett wrote:

That's an oldie. My Dad's version was "a one-armed paper hanger with an itch". And yes, I now recognize that the choice is between building separate units and bursting a blood vessel in my temple. I'm leaning toward the former.

I've only used regular yellow wood glue, for wood anyway. I have used two part epoxy for other things. Is there epoxy especially for woodworking?
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Greg Guarino wrote:

No but there are various hardeners which cause the epoxy to set up slower/faster.
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dadiOH
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"Greg Guarino" wrote:

-------------------------------------------------------------------------------------
------------------------------------------------------------ There are lots of epoxy suppliers out there.
There are only 3-5 manufacturers of part A; however, there are litterly hundreds of part B suppliers which is where all the black art of formulation gets involved.
WEST Systems probably has the widest distribution.
I have a preference for System3.
http://tinyurl.com/bx584yx
Epoxy is basically an adhesive, it works very well gluing wood together.
You want standard laminating part A resin and the slowest part B hardener for this project.
You will make life easier at assembly time by toe nailing shelves into grooves at assembly time, then clamping at final assembly.
When using a router for dado grooves, easiest solution is to make two passes using a jig.
Leon has a jig he developed for the purpose.
Maybe he will post details again.
Lew
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Greg Guarino wrote:

Sure, you have our permission to do that. Mine at least.
For that matter - should you want the shelves in the same plane - you can cut the dado all the way through except for a few inches at each end and notch the shelves appropriately.
A variation on notching the shelves would be to make rabbets...on one shelf, make a 3/4 x 3/8 rabbet on the top; same on the other shelf but at the bottom. Rabbet size depends on ply thickness but the goal is to have one shelf rabbet resting on the other.
Still another variation that comes to mind would be to make a series of half through slots, each maybe 2" long from each side but staggered so that none go all the way through. Then cut fingers on the shelfs.
One of the joys of woodworking is that with a fertile mind one can come up with all sorts of ways to complicate things. :)
--

dadiOH
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On 12/12/2012 5:27 AM, dadiOH wrote:

Definitely. A novice like me can come up with some really "special" ideas. Trust me.
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Perfectly OK to make dadoes in both sides of the center divider, even if they are in line with each other, as long as you fill them with shelf.
--
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On Wednesday, December 12, 2012 3:02:53 AM UTC-8, Swingman wrote:

I'd add a caveat, there ought to be LONG GRAIN extension of the central ply through the thinned region. It's possible to orient the plywood so that thinning it leaves only/mainly one ply, with grain parallel to the shelf. That's gonna break REAL easy. Maybe won't survive attempted assembly.
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On 12/15/2012 4:54 PM, whit3rd wrote:

OK, which ply is the "central" ply?
Most, if not all plywood has an odd number of plys by design, specifically to mitigate warping.
It's possible to orient the plywood

Not so sure about that, especially if the dado fits what's going into it.
> Maybe won't survive attempted assembly.
That's a pretty strong statement ... got anything to back it up with?
Literally thousands of this type joint under my belt and have never seen, or heard of any instance, of that happening.
All that means nothing in the greater scheme of things, basically, I'll continue to take my chances that, providing everything fits as spec'ed, it ain't gonna happen. :)
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