Often the sewing thread in one or two signatures will break while the rest of the text block sewing is sound.
In this case, tipping or hinging the separated signature(s) into the book is not the best option because those methods do not give enough support to so many pages. Also, hinging-in pages adds several layers of thickness to the spine of the text block. The extra thickness can put stress on the case hinges and interfere with the pages opening easily.
Resewing an entire text block takes time and practice and should only be attempted when the book is to have lasting importance. Before resewing a text block, study the sewing structure.
Open the text block to the center of a signature and look at the sewing threads. Books sewn by machine usually have double threads and no sewing supports (tapes or cords). This kind of sewing is called unsupported sewing because only the sewing thread and glue hold the signatures together. Most manufactured books are constructed with unsupported machine sewing.
Text blocks that are sewn by hand usually have single sewing threads sewn around tapes or cords for support. Some manufactured books are also sewn on tapes or cords. This type of sewing is called supported sewing. Supported sewing is always stronger than unsupported sewing because the tape or cord helps support the signatures.
The link stitch is used to repair a text block sewn using unsupported sewing. In unsupported sewing, the signatures are linked to one another only by the sewing threads.
The lap-link stitch is used to repair a text block that is sewn on tapes or cords. This is called supported sewing because the tapes or cords provide the supporting connection between the signatures so there is no need to link the signatures to one another.
Work through the instructions at least once before attempting them in the book you wish to repair. Fold pieces of paper to create signatures, punch sewing holes and number them so the directions are easy to follow. Save the practice signatures to serve as a model for future reference.