Unpopular opinion: stop gluing your spine linings before rounding, I wasted 3 years doing that
I used to glue my mull and paper lining on flat before rounding, thinking it would hold everything tight. Two years back I was working on a 400 page rebind for a guy in Portland and the spine cracked right at the hinge after one month. I sat there staring at it and it hit me, the lining had no give, so all the stress went straight to the joint. I tried rounding first and linings after, just 3 books as a test, and the difference in how the text block opens is night and day. Now I round, back, then line, and I have not had a hinge fail in 18 months. How are you all doing your spine work, lining before or after rounding?