Recently there have been a number of people asking where to get larger sheets of ply. They can be difficult and almost always are very expensive to get. I know that the experienced woodworkers here know this technique, but I thought it would be a handy thing for some of the newer builders to see. If someone would like to document scarfing ply, that would be great. There are several ways to stretch your plywood, here's one method.
This technique uses a router and if you don't have a router....well, you're going to need one anyway as it's a real versatile tool. Pick up a 3 wing cutter. Shown is an 1/8" one but they are also available in 1/4". It will cut a 1/2" slot into the edge of the ply. The 1/4" one will cut a 9/16 wide slot.
Adjust the cutter so that it is approximately cutting in the middle of the ply. I mark the side that I rout from so if it's not dead on, the sides will mate up fine anyway. Rout all the slots for the matching pieces.
I cut splines out of baltic birch ply. It's a true 1/8" ply so it's a dead on match to fit the slots. I rip them just a hair under 1", if there is any crud in the slot or they are too wide, the ply will want to sort of kink at the joint. A little narrower takes care of any of that. Baltic birch is also stronger than a lot of the cheap plys available when using small pieces.
Glue it all up, make sure to butter the sides of the spline really well and the edges on the ply sides. Weight and clamp, watch too much end pressure with a clamp however. I use epoxy as it gives me more working time, however Titebond works well also.
It's a real easy/quick way to make up whatever size sheets you want. For a woodie...I use a lesser substrate, then laminate up the nice thin veneer ply over it, making sure that the joints don't fall on top of each other. I've done this on 5 trailers so far and it works great for me. I made some 6'4" x 11' ply this evening. Doug