A shop regular in Baltimore told me my case binding was too tight, and I'm still not sure if he was right
He said my signatures couldn't breathe in the spine and the book would crack in a year. I loosened my stitching gaps from 3mm to 5mm and now I think the boards feel flimsier, but he's been binding for 30 years so who am I to argue. Do you all leave more slack in the spine or keep it snug?
So the guy who has been binding for 30 years never made a book that cracked in a year himself? Look, there is a real thing here, which is that the spine should not be so tight that opening the book puts all the stress on the first and last sections. But 5mm gaps on every stitch everywhere is not the fix people think it is. What you actually want is a bit more give near the spine and a firm, even pull through the rest of the section, not uniform looseness all the way across. Loosening everything is why your boards feel floppy now, because the whole text block lost its backbone, not just the part near the hinge. Go back and check how the book opens at the middle and at the ends, and if the middle still lies flat and the ends do not crack, your original 3mm may have been fine all along.