Designer binders, conservators who replicate wooden boards with laminated museum board, and others sometimes have to create a bevel or chamfer in book board. Often this is accomplished by sanding, which is at best a very slow process, and at worst an easy way to create a disgusting amount of dust. A downdraft table and PPE is recommended.
Beveled book boards were very common in the nineteenth century. Various contraptions were invented to do this, including a specialized board shear that cut at 45, rather than a 90 degrees, a jigged foot clamp and large chefs knife, and a machine that used a woodworkers jack plane running in a track. Large production shops sometimes had a board beveling machine with a rotary blade, but most of us are not so lucky.
As the video below illustrates, it is also possible to bevel binder’s board quite efficiently with a modified 151 spokeshave, a tool which is usually used to thin leather over large areas. Note how much I skew the spokeshave, and how it is in motion when I start the cut. Also listen to the sound: this is what a properly adjusted sharp blade sounds like. Even after spokeshaving, it may still may be necessary to refine the board edge a bit with some coarse sandpaper.
If you are laminating your own boards (de rigueur for high end work), it is a good idea to paste a few layers of colored paper to the level you intend to bevel, in order to judge how deep you are spokeshaving. Since binder’s board is quite abrasive, an A2 or PM-V11 blade is a necessity. And the blades do wear more quickly than when shaving leather. It would be smart to dedicate one blade just for board.