Cutting with a saw several kerfs or channels across the back of the book is the next operation, and this is to allow of sewing. In order to do this, the book (either one or many) is screwed up in the lying press, either between pressing boards or backing boards, which are placed slightly below the level of the back to allow the cut to be made. If a lying press is not available, an ordinary carpenter's bench will answer the purpose. The back or the book is, according to its size, now divided into a certain number or spaces, mostly equal; but owing to a common optical illusion, in order that all the spaces shall appear to be or the same size, the bottom space must be about ½ in. larger than the others. At the points of division lines are drawn across the back of the book, and these lines mark the bands or cords on which the book is to be sewn, through, for ornamental purposes, books are often marked up for, say, five bands and only sewn on three, the dummy bands being fastened on when the book receives its cover. In flexible work the back is not sawn in except for the kettle stitch or catch­ing stitch, the bands or cords being outside the sheet, the thread being sewn around them. In the other kind, the back is sawn across at the places marked, the cut for the kettle stitch being very shallow, only deep enough, in fact, to take a chain stitch or single thread. Octavos are generally sawn for five bands; larger or smaller books have more or fewer bands, according to size, because in the larger books the number of leaves in a section are few, and the thread has less substance to hold on to than in the smaller books.

The twine or string used for the bands varies in size according to the size of the book; it is named after it, and is sold by that name. In the case of large books, where the cord is thick, a plan that has been successfully adopted is to use two pieces of thin cord instead of one thick piece. This method has much to recommend it.

The cuts, which are made with a tenon saw, should be perfectly level, should not be deeper on one side than on the other, and should be just large enough to receive and hide the cord. If the saw has a thin blade. it should be inclined just a little alternately to the right and to the left, so as to widen the bottom of the kerf. Fig. 32 shows the saw kerfs.

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