Secure the ply to the waste board (you can add a sacrificial wasteboard to save damaging the main one, since through holes will be bored), avoiding tool paths.
Carve the ‘Top’ side (http://easel.inventables.com/projects/E9_B6qXc9qOYPxGpKFK82g).
Remove the ply and turn it over.
Insert 6mm dowels (or similar pins) into the two alignment holes that were bored into the wasteboard.
Align the flipped ply, using the dowels, and secure it.
Carve the ‘Back’ side (http://easel.inventables.com/projects/yWDbkEVnXPXk2ReA8kyrOw).
Make copies of the easel files and add text and/or logos to a depth of <1mm. Delete the boomerang paths, and then carve your designs on the boomerang.
A light sanding will relieve all the sharp edges, and a coat of polyurathane will add protection.
This size and weight boomerang works well when there is no wind. Try experimenting with size and thickness to make ones that work in other conditions.
It’s taking me a while to get the hang of flying, but I have sent the boomerang over 50m away, and caught it on it’s return about a dozen times, with about 3 hours of ‘flying time’.