Board beveling and its applications in bookbinding
Cutting devices in the graphic industry (guillotines, board cutters...) produce 90 degree cuts by default. But what about 45 degree angles?
A powerful bond
45 degree edges (bevels) can be found in joinery/cabinet making, picture framing, mirror making and more. The reasons are often aesthetic, and in some cases technical, particularly when they are used for joining.
The diagram below shows two ways of connecting boards in box making 1) the conventional way and 2) using bevels. It only takes a quick look to realise the superiority of option 2. We can see that with beveled edges, the contact surface between the boards is increased, meaning a stronger bond. We can also see that the problem of weakness due to cardboard delamination, (illustrated in the middle diagram) doesn't apply to option 2.
45 degree angles also produce wonders in the world of hinging. The diagram below shows hinges made with 1) regular boards and 2) beveled boards. In the first scenario a very substantial gap is needed between the two pieces, and the heavier the boards, the wider the gap. This means less support, and problematic turning in, especially with non stretchy materials like paper or vellum. This also means that with such a construction the top piece will have a tendency to sink in over time as no support is offered by the spine piece.
Like magic, all of these issues are fixed with beveled edges: the spine piece naturally supports the top piece, the gap needed is minimal (regardless of board thickness), turning in is facilitated and the result is often a crisper and neater looking edge.