Fig. 37—Top edge arranged for trimming when trimming three edges.
As our machines are made to cut from left to right, the book back must be on the left.
Very often a book contains so many folded plates that it is considerably thinner in some places than at others. These thin places must be properly packed with paper or strips of board, otherwise the knife is sure to tear or jag, no matter how sharp it may be. This packing may be left in the book until the book is quite finished and then taken out.
If any fibrous matter has stuck to the bottom sheets through cutting on a much-used bed, it must be removed with a very sharp knife.
The trimmed volumes are "rounded," i.e., they are rounded and the groove made at the back to which the boards have to be fitted. For this reason the grooves must be made to suit the thickness of the boards to be used.
Fig. 38—Rounding the book.
To round a book, slightly damp its glued back, place it on a firm stone or metal bed, and knock it round with a hammer. Properly speaking the process is as follows: The left hand takes hold of the back of the book lying flat before the worker and works it into a round form, the right hand helping all the time by beating it along the back from one end to the other.
In this way each side is treated alternately until the back is evenly rounded. The rounding of the fore-edge should be equal to one-third of a circle.