I had to join sheets of ply for two long tables recently and made up this jig. I usually do this process by hand but this was a bit quicker. It would be nice to do it on a vacuum bed as my bench is'nt so flat and neither was the ply but it got me close then I adjusted by hand planing. I allowed a little extra width in the sheets for the inevitable misalignment. I cut both boards at once so you know the angle is the same - a habit left over from doing this by hand.

I used a big 32mm bit and made a carriage for my router that slid along in between the straight edges, which slid up and down the 6:1 angle guides mounted on the side of the bench. See images of the tables (the two longer ones) on this page table all-ply designed by usethings