0

I was thinking about making a pantry cabinet using 3/4" plywood. To join them, I was considering using mortise and tenon joints between the sides and backboard. I couldn't find any youtube videos of anyone making mortise and tenon joints using plywood and so I'm guessing it's a bad idea. Are the plys too thin to make a strong tenon?

If I wanted to make a cabinet using only joinery / with no nails, then what joints should I he using? Rabbets and dowels?

  • Why punish yourself, do dado’s or use solid wood ! – Alaska Man Jul 13 at 8:32
  • 1
    A slightly different approach to this would be to glue different pieces of plywood together, leaving room for the mortises and creating tenons. That way you don't have to remove layers of plywood. So, in those cases rather than using 3/4" plywood, use 1/4" plywood and glue 3 boards together leaving space for the mortises and on the other ones, making sure the tenon sticks out – Kenneth Jul 13 at 12:05
  • "Are the plys too thin to make a strong tenon?" It's not that the plies are too thin, it's that there are plies to begin with (remembering that each ply is at 90° to the next, so there's an inherent weakness to small/narrow projections of ply). Why even envisage M&T's with ply when other options abound? Just look at how plywood cabinetry is usually done and picking an option is undoubtedly the easiest approach here, although aesthetic choices can trump other considerations [contd] – Graphus Jul 13 at 15:44
  • So if you want to stick with M&T you can, but it would generally be best to do what almost amounts to a captured finger joint.... which then suggests the option of using finger joints (box joints) to start with. Finger-jointed corners are quite common in plywood with users who don't mind the exposed plies in the finished item (or where they're painting) and additionally this is likely to make for the absolute strongest box possible in the material because of the huge glue surface area and the mechanical interlock of the joint. – Graphus Jul 13 at 15:49
  • @Graphus I'll look into the finger joints. I should have mentioned in the original post that the reason I'm using plywood is due to cost. I wasn't able to find reasonably priced boards near me. When I looked for plywood cabinets on YouTube, all I found were pocket screws. For the sake of learning I'd like to avoid pocket screws. – Huckle Jul 13 at 16:16
3

Plywood doesn't really work with traditional joinery. Because it is made from alternating plies or other composite construction it is hard to make a snug tenon fit. Further, many of the joints will be mostly end-grain. Both of these issues make tight glue joints nearly impossible with those sorts of joint. And, though the outside ply will readily work well with PVA glues, the internal plies themselves may be constructed with glues and additives that do not work well with PVA. This generally makes for an ill-fitting, weak joint that does not take advantage of how PVA glues work.

You'll find most plywood construction is made with biscuits, dowels, or pocket screws. That is, most plywood construction makes use of fasteners for aligning and providing some additional stiffness.

Depending on the application, you might get away with finger-joints if that was a construction detail that appealed to you. It may not be tremendously strong, though. It may depend on the rest of the construction and the type of plywood. But it is generally a reasonable option for many.

Finally, I suppose you could experiment with what boat-builders do with plywood. They tend to use mechanical fasteners as well, but where they don't, they often use epoxies and other special adhesives with lap-style joints to provide strength with flexibility. A special case, maybe, but it points out one of the first major industrial uses of plywood materials.

| improve this answer | |
  • Good Answer. But finger joints are tremendously strong in ply, certainly far stronger than many alternatives, including my personal favourite which makes use of dowels in some manner (even when used a little unconventionally with some dovetail/toenail component). Obviously it does depend on the quality of the plywood, but that also applies to nearly all other common joining methods using the material...... possible exceptions including internal glue blocks and epoxy fillets which bypass the internal structure. – Graphus Jul 14 at 15:57
  • Certainly the times I've used finger-joints is in box construction, where the structure itself supports the joint well. I guess you get at least one side of really good adhesion, and if the cuts are clean perhaps the edges of the plies act a little like a biscuit and swell up. I've never felt that confident on any plywood joint that involves end-grain and glue only. Oh well, I can modify my answer a little to reflect that instead. – jdv Jul 14 at 17:00
  • "I've never felt that confident on any plywood joint that involves end-grain and glue only." Oh yes, totally. Even using the very best ply made a simple end-to-face butt joint cannot be particularly strong. – Graphus Jul 15 at 8:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.