In my world, 0.4" is not thin at all. Shop sawn veneers are usually 0.125" and guitar parts are routinely 0.08". Your wide belt sander is your friend. I would think 10" lengths should be fine, just butt them end to end while running them.?
My sander has a .125" limit switch, so I have a variety of carrier boards for thinner material. They are just MDF with a hardwood strip glued/screwed on the end to stop the piece from becoming a projectile. It will happen without this.?
Jason Holtz J. Holtz Furniture 3307 Snelling Ave. South Minneapolis, MN 55406 612.432.2765
-- Jason J. Holtz Furniture 3307 Snelling Ave. South Minneapolis, MN 55406
Jason Holtz