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.
Peachey Conservation 
How about using a dremel with the rotating sanding piece?
That can also be used for thinning leather. It gives a mess but is easy to yse and very precise
Yes, any type of sanding makes a huge amount of dust, which I try to avoid. Although the drum sander attachment is quite small, this makes it more difficult to thin a large area of leather evenly, at least in my experience. It think it is easier on binder’s board. But if you really want to sand it, I would use a belt sander. Ann Lindsey compared a number of methods on chrome tanned leather in 2002: http://cool.conservation-us.org/coolaic/sg/bpg/annual/v21/bp21-21.pdf
I use the dremel with sanding drum only when thinning the edges.
Yes, I understand.
I use a low angle block plane to bevel wooden boards, fairly quick, good control. Wouldn’t that work for laminated boards, as well?
Maybe, although low angle block planes are bevel up, so the included angle is often steeper than a bevel down spokeshave where the sole has also been lowered. Try it and let us know how it works!