I am making a box out of 3/4 ply and want to use routed joints for the corners.
Are there any issues with lap joints on plywood?
Hi Bryan; not too sure what your def. of a lap joint is. I recommend a drawer lock bit for routered corners in ply. Depending on the direction of the ply you may have to score the outer layer to minimize tearout, but it makes a real nice mitred corner and is rather easy to set up the bit on a router table.
One concern is that there might be tearout if I cut part way through a layer of the plywood. It seems better to have a joint that limits the depth of cut to one of the ply layers.
Need more information, Bryan. The type of joint that is best suited will depend on what you are making. If your are making a box and the joints will be vertical, then the drawer lock bit or finger joints will be better.
If you are making a flat joint, similar to rail/stile or picture frame, then a half lap should be fine. Try to ensure that you route to a depth that hits the lamination between two plies, as close as you can, and doesn't take off any significant portion of a ply.
Also check to make sure that the plywood itself isn't junk like so much of what we get these days. It does no good to do a nice strong glueup on the lap joint if the laminations between the plies above or below are crap or one or more of the plies is just soft punk.
The box 25x50inX8in deep and will have vertical joints. I like the drawer lock bit but since it cost $45 (from Lee valley)I would like to use one of my existing standard bits so a box joint could be done. I want to use the router to build experience using it.
The box will in fact be an apron around the top of a mobile work table. The table top is a loose fit inside the apron so that it can be reversed for different uses.
The appearance is not an issue but since I will be using the apron (box) for clamping on all four sides I want it to be 90 deg to the top.
The legs will be made from scrap 2X's (I have a lot to use up) and there will be a sub deck for power tools underneath and perhaps some shallow drawers under that.
A good strong corner plywood joint for a box where esthetics is not involved is a half lap joint together with screws. The mating piece is bored for a cross dowel where the screws go. So....you bore for the cross dowels,glue them in and sand both sides smooth, pre-drill for the screws, counter sink for tapered plugs, slap on the glue, run in the screws, viola a very strong plywood corner joint, glue in the tapered plugs, sand smooth & it don't look half bad.