: I've practiced on two scrap pieces, making a top and bottom scarf to use as
: guides for when I do several pieces clamped together. I was surprised at
: how easy it was to do with a block plane. The tip to run the plane down at
: a 45 degree angle was great - from Chris K's kayak book.

: The only "problem" I had was that it's really hard to avoid cutting
: all the way through that bottom layer of veneer, creating a feathery
: looking edge instead of a straight line. Will that just blend in and not
: be noticeable? Is it more important to get it really, really thin so
: there's not a bump than to keep a straight pretty line?

You want to get that edge as thin as possible to blend it in with the top of the other side and leave NO ridge showing above the flat surface. If you have that ridge and then sand it off, you will leave some of the inside veneers and glue line of the plywood exposed and ruin your whole day. Just don't feather too far or you will shorten one piece and leave a gap at the joint which will agian expose some of the plywood edges. It sounds like you are doing just fine.

: Also, is it possible to plane too much so there's actually a little give if
: you pinch the joint? Maybe the epoxy will fill that up if you go too far?
: Otherwise, I would think it would be weak.

If you are keeping the bottom surface of the plane on the material, you should not have hollows in the joint. It will be perfectly flat. On the other hand, some plywoods may have a tendency to cup a little after you cut them. This would be because the inside wood may have a little more moisture and want to dry and curl, or just the grain in the plys curving. When you put the joint together with glue and then weight it down, that should all be taken care of. The biggest problem to be avoided will be alignment of the joint so that your plywood planks are straight and not scewed a little. Get the alignment right and the overall length ( if the panels are precut ) and the joint will take care of itself.
Hope this helps!

Rehd