Through-tenon vs half-lap joints in plywood furniture
The short answer: a half-lap lets two parts cross each other, each with a slot that takes half the other's width. A through tenon is a tab on one part that passes right through a hole in another. Both need no screws or hardware, and a CNC cuts them easily in plywood.
Half-lap joints
Each of the two parts has a slot, and the slots meet so the parts lock into one plane, flush on both sides. They are the joint of a bookcase, where every shelf crosses a side, and of crossed table legs. They are simple, quick to cut and quick to assemble, and they keep the parts square.
- Good for: shelving, crossed legs, dividers and any grid.
- Watch out for: the slot weakens each part where it is cut, so keep them away from the middle of a long span.
Through-tenon joints
A tenon on the end of one part goes through a mortise in another and shows on the other side. In the benches, chairs and tables here the leg tenons go through the top or the seat, and a stretcher passes through the legs held by wedges. The joint has a large glue area and resists racking.
- Good for: legs to top, stretchers, and any joint that takes stress.
- Hidden option: on tables you can choose a clean top, where the tenons go into pockets underneath and nothing shows on top.
Wedges
A wedge driven into a tenon spreads it and locks the joint without glue. It also lets you take the piece apart for storage, and tap the wedge in again if the joint loosens.
Glue or no glue
For furniture that takes daily stress, such as a chair, glue every tenon and clamp until it dries. For furniture you want to take apart, leave it dry and choose a slightly looser clearance. A fit test tells you which clearance suits your board.
What changes with a CNC
The router leaves rounded inside corners, so the files add dog-bones where a square corner has to seat. Slot widths come from your real plywood thickness: see why 3/4" is not 3/4".
Frequently asked questions
Which joint is stronger?
It depends on the piece. Through tenons give a large glue area and resist racking; half-laps are simple and let parts cross each other. Both work best glued.
Can I take furniture apart if I glue it?
No. Leave a joint dry if you want to disassemble it, and choose a looser clearance for those parts.
Do wedges need glue?
Not necessarily. Wedged tenons stay tight by themselves and can be tapped in again if the joint loosens.