Serious question, the guy at the paper shop in Baltimore told me never to crease a spine before sewing
I was picking up some sheets at a supply shop on Charles Street about 3 months ago and the older guy behind the counter watched me fold a signature with my bone folder and he said I was doing it backwards. He claims you should never crease the spine fold before sewing because it weakens the paper and the thread should set the shape instead. I learned the other way in a workshop years ago, crease first so the signature sits flat, and it has worked fine on maybe 40 books for me. So which side is right here? Do you crease first or let the thread do the work?
Folded plenty of signatures flat before sewing and thought that was just how it was done, till a bookbinder showed me how creasing the fold actually breaks the fibers right where the thread needs to grip. Letting the thread pull the shape means the paper stays strong at the spine and the section still opens fine once it's bound. Took me a few books to trust it but now I crease after sewing, not before, and the old guy was right.