I'm building a book case out of melamine. The drawing below show the normal and exploded view. Dimensions are 110cm wide, 30cm deep, 126cm high (~43"x12"x50")". I'm worried about the stability of it, since it needs to support quite a bit of weight. The white panels are 3cm (1 1/4") thick, the "wooden" panels are 1.9cm (3/4") thick.

I have reinforced the side with steel rods and plan on adding washers and nuts on there (not shown in the drawing) to make the ends more sturdy.

I have a couple of questions:

  • In general, do you see any issues with the weight it needs to support? (the largest span is 45cm (17 3/4")). According to what I saw for melamine of this thickness, that should be fine
  • Do you see any obvious issues that could cause racking? I added the steel rods to prevent this
  • And my biggest issue: In the exploded view, where the red reference line is drawn and the horizontal cross supports connect to the upright support, I'm not sure which type of joinery to use. I don't want to add screws from the outside in. I thought about either dowels or pocket screws, but I'm not sure whether they will be strong enough to support the weight.

book case melamine

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    Sorry, have to check. When you say "melamine" are you referring to chipboard/particleboard with a melamine surface? Can you also please clarify what you mean by stability here. Most woodworkers (I think) are going to assume you're referring to resistance to racking, and/or tipping, when I suspect you're mostly concerned with resistance to sagging? Or is it a bit of both? – Graphus Nov 5 '20 at 9:16
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    Dowel joints are strong to hugely strong — matching or exceeding both M&Ts (!) and Dominos — so you should have no reservations about using them, if you can get the holes drilled to align accurately (although sloppy fit is no longer an absolute dealbreaker, since we can now restore lost strength by glueing using thickened epoxy). If no external fastening is acceptable they would be my #1 choice here, since the hold of the screws typically used in pocket holes would be an open question... one best not answered in the negative by a problem down the line :-) BTW assuming hardwood dowels here. – Graphus Nov 5 '20 at 9:23
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    "I added the steel rods to prevent [racking]" - Not to nitpick, but the steel rods won't add any strength against racking. To prevent racking you either need supports running from corner-to-corner or joinery wide enough that it won't twist. In this design the main anti-racking (left-to-right) support would be from how far apart the two dowels are joining the vertical pieces to the top and bottom horizontal pieces. I would also be very worried about racking front-to-back, which has very little support in this design. Anchoring it to the wall would prevent this though. – SaSSafraS1232 Nov 5 '20 at 17:14
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    Sagging could be an issue, but it all depends on the specifics — the quality of the material (it's far more varied than one would expect, and the full weight being supported by each shelf. There is obviously a potential for it to tip forwards, as with all tall structures like this, but it's simple to attach the uprights to the wall with tethers to obviate this concern. – Graphus Nov 6 '20 at 6:29
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    @AloysiusDefenestrate, it's not a 4" unsupported span — the Q specifies, the largest unpported span is a mere 17 3/4". Course this still does not mean there's no potential for sag, but my gut says it's not likely unless the books are unusually heavy. I've had many particleboard bookshelves in my life and very heavily laden with paperbacks (double stack, double row) an approximate span of 1m does most definitely sag, and this is less than half that. – Graphus Nov 6 '20 at 6:35

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