Cutting the edges is performed with the plough at the lying press. The operation is termed cutting in boards. The plough knife should be carefully ground and whetted, or good work cannot be done. The head or top of the book is cut first, the back being towards the operator. A cutting board is placed behind the book, and a straight runner along the millboard and level with its edge; the book is then placed level in the press, which is screwed up tightly. When the head has been cut, the tailor bottom of the book is treated in a similar manner.

These operations are simple enough, but cutting the fore edge or front of the book presents more difficulty, as it is necessary that the curved back should first be rendered flat. This is an operation that requires considerable care, and if the amateur cannot obtain a little personal instruction on this point he is likely to spoil many books. The operator holds the book in his left hand, permitting the boards to fall back flat, and passes a piece of string once or several times round the book. He then pushes a couple of pieces of thin beveled iron termed trindles (see Fig. 38, p. 57) between the book and the boards at the head and at the tail. Taking the book between the palms of his hands, the operator now beats the back of the book quite flat on the cheek of the press, the cord and trindles helping to keep the back flat. Having made the book flat, and having marked the front edge of the book back and front, the operator places a cutting board level with the mark at the back of the book, and another cutting board, or a long, straight runner, a little below the line on the front (or right hand), and, striking out the trindles, lowers the book into the cutting press, the millboards hanging down.. The distance below the mark at which the runner is placed must be equivalent to the desired square for the board at the fore edge. When the volume is in the press, if it has been kept level, the runner must be level with the right-hand cheek, and the other cutting board must stand up for the distance of the size of the square above the left hand cheek. When the book is correctly fixed, the press is screwed up tightly, and the front edge of the book is cut with the plough as before. When the book is taken out of the press the back will resume its convex shape, and the fore edge should present a regular concavity.

As the cutting of the edges of the book is a very important operation, the following points must be remembered. The edges must be square with the printed lines on the page, and should not be trimmed more than is necessary. The margins of white paper on a page must bear a certain proportion to each other. The printer, when preparing the pages for printing, settled the margins for the page, and fixed also the proportions. The binder cannot improve on this arrangement, but he can spoil it altogether by bad cutting. The white paper at the top of a page, measured from the type (excluding the headline) to the edge of the paper, and the white paper at the front of a page, measured from the type to the edge of the paper, should be of equal width; the white paper at the bottom of the page, measured from the type to the edge of the paper, should be about one-fourth more than the front or the top margin. Thus, if the front margin and the top margin are each 1 in., the bottom margin should be 1 ¼ in.; the back margin in such a case would be ¾ in., and as this margin cannot be trimmed, the width of it compared with the other margins shows at once whether the book has been properly cut. It will be readily understood now that good and accurate folding is of the greatest importance, because the cutting of the edges of a book magnifies any errors committed in folding. The trained eye, however, is a better guide for mar­gins than the measuring tape. The book covers must be absolutely square to the paper, as the paper is to the print; the covers must not overhang the book too much, and the amount of overhang must be in the same proportion (the difference, of course, is only enough to be just perceptible) as the margin is to the printed page.

Books bound in cloth or in other cheap styles have their edges cut on the guillotine, as the use of the plough is too expensive for cheap repetition work.

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