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I am building a movable narrow island / kitchen prep table out of plywood and would like to know what would be the strongest joint for it. It will be mostly supported by the cabinet box sides which are 48" long and 32" tall. The cabinet will be 16.5" wide. I think a 90 degree butt joint on the bottom will be stronger since the weight of the sides will be directly on the bottom board rather than transferring the side load through the pocket screws. The top will have a granite slab so there will be a lot of weight on the cabinet box. Ignoring any finishing or what looks better, what is going to be the strongest method between a 90 degree overlapping butt joint versus a pocket screw. I was also thinking of doing a rabbet joint on the bottom but then I would have to adjust the pocket screw a bit and do the rabbet which takes more time. Drawing not to scale, it will be much taller.

Additional info: I am filling the cabinet with drawers on each end. There will be a center vertical board in the middle to help stabilize and split the cabinet box.

Pocket vs. 90 degree butt

Updated: Here is the solution I chose

Rabbet Joint 90

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    While it is entirely possible that the second option would work fine in practice, with the screws used (not the generic type, the exact items), and the number of them, of course being important considerations. But your first option would be far preferable IMO, and in absolute terms I think it must actually be stronger. – Graphus Oct 19 '18 at 19:00
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    What @Graphus said: first option, all day, every day. (Especially since you've got stone on top.) The second version doesn't transfer loads to things that can carry them. – Aloysius Defenestrate Oct 20 '18 at 4:46
  • Regarding my debate with Ast Pace below, if you go with option 1 you will be fine if you do this neatly and esp. if you choose the right screws. But if you want to avoid even the possibility of a problem with screws used in this way simply switch to dowels instead, see this other current Answer. – Graphus Oct 22 '18 at 18:52
  • @jdv I did 18 minutes ago. Bottom image, it is very solid. I also did put a few longer through screws – Enkode Dec 12 '18 at 17:01
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You mention that the bottom is plywood, which leads me to think that the sides are plywood also. It is never a good idea to drive screws into the edge of plywood. Not even if the joint is not carrying a particularly big load as in option number one.

You should use solid wood gluing blocks to reinforce the joint. The blocks are placed in the corner and then screws should be driven into them through the horizontal plywood bottom and through the vertical panels into the blocks.

So, use option one with gluing blocks. The blocks have to be large enough to take the screws without splitting - pre-drill and use wood that's in the range of a 2x2

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  • Eees not dis seemple. While glue blocks are certainly an option they're hardly the most elegant reinforcement and I think they're more suited to utility projects. And even though it is much derided screws are very frequently used in plywood cabinet construction, and always have been, sometimes with tweaks to give greater security (e.g. cross-dowels or glue in the pilot holes) but sometimes not. – Graphus Oct 22 '18 at 12:51
  • @graphus we gave up on elegance when pocket screws were introduced by the OP. True, plywood cabinetry often employs screws, the screws are still anchored in solid wood and driven through the plywood. – Ast Pace Oct 22 '18 at 15:20
  • Thanks for the answer, I am planning on adding drawers to each end. This is not ideal but might be a solution. – Enkode Oct 22 '18 at 16:31
  • LOL About the second bit though, I actually did mean screws going into the edges of plywood not through its thickness, sorry if that wasn't clear. Screw length alone can make a big difference to the commonly supposed idea that you can't get a good hold screwing in at the edge, and the earliest plywood guides actually cover both screwing and nailing as means to reinforce the glued butt joints. – Graphus Oct 22 '18 at 18:46
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A lot of good points were commented but as a solution (much appreciated) I chose to use a 3/16" rabbet joint on the bottom board and then pocket screw and glue it in. The rabbet joint provided a nice grove to keep the the box square. The pocket screws I just used were 1" and the plywood is 3/4" so I had to be delicate with not over drilling them but I think that goes with most 90 degree pocket screw joint.

Pocket vs. 90 degree butt

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