One way of doing it is with a butt block, a piece of plywood which overlaps and is glued to both parts of the plank. A butt block is not only unsightly to some people but can also create a kink or "hard spot".
A scarf joint is the method that most boatbuilders use. Traditionally cut or planed in a long bevel, it has the advantage of creating a smooth transition between the sheets of plywood, and also increasing the bonding area for greater gluing strength.
The stepped scarf that we use is cut in a series of steps
that are 10 times as wide as they are tall,
making a 1.2" long scarf in 4mm
plywood. Not only is this joint very strong,
but it has two advantages over the
traditional tapered scarf:
- the edge is much
sturdier than the sharp edge of the traditional scarf joint
- the steps are self-aligning making the joint easier to assemble and giving the planks a more accurate shape