: . . . "Why
: not just make a shiplap joint the length of the scarf."

Ya know, I think they call it a ship lap joint because it is used i ship building.

: That got me
: thinking. Why not make a stepped joint with just one step?

That would be a half lap joint.

: It doesn't make
: sense if you're cutting the joints with a plane, but it does if you're
: using a router.

True. Cutting across the grain of every other layer of veneer in plywood could get to be a problem with a handplane. An electric plane set up for rabbeting might do the job far faster than a cnc router.

: And, how many steps does it take to effectively mimic a
: bevel cut scarf joint?

rather than worry about mimicing the effect of a scarf joint, why not try to mimic the construction fo the plywood.

Every layer in the core is made up of layers of veneer which are butt joined together, and supported by being backed by the layers of veneer which are above and below them. For good strength the joints in the layers should not be in line with each other. Making a stair step joint, with each step being the thickness of that layer of veneer, you woudl effectively duplicated the conditions of plywood.

The wider the steps the better and stronger the joint, but with modern high-strength glues, even a 1/2 inch-wide step for each veneer layer should give a nice joint. With 3-ply wood you would have two steps.

If you simply routed out a piece so it was half its original thickness, you could use this for a half lap joint. For 3mm plywood, you owuld rout down 1.5mm, for example, and make the cut 2 inches wide. (that would be several passes. Usign epoxy for the adhesive gives you a bond which is much stronger than the wood around it. I wouldn't worry about flexibility or strss risers in wood joined this way. The resindoes a great job of filling gaps, and as it is stronger than the wood, cracks which might concentrate stresses are effectively filled in.

Then they are covered with glass fabric, so all the worries are buried under resin and glass fibes.

PGJ