Book trimming is one of the final steps in thermal binding or perfect binding. Trimming cuts of the unfinished edges of the book to create a perfectly square book. Customers prefer a clean cut with no damage to the book's cover. Book trimming machines are different from typical guillotine paper cutters because they are specially designed for cutting books without damaging the spines.
Trimmers come in several main varieties. There are full sized three-knife trimmers that have a dedicated knife for each cut. There are also single-knife trimmers that use a single knife and rotate the book for three cutting cycles. As you can imagine, three-knife trimmers are much faster but more expensive. Single knife trimmers cost considerably less but have a lower throughput speed.