It took a $60 buckram order arriving wrong to figure out I'd been measuring covers wrong since 2021
I've been cutting cover boards by adding 3mm to the text block on every side and calling it good, which seemed fine until a customer brought back two books from my spring batch with covers that stuck out past the fore edge like little porches. What tipped me off was a stack of buckram I ordered pre-cut at 9x12 for a run of 10 octavos and half of them came up short at the hinge, so I sat down and actually measured the gutter allowance instead of eyeballing it. Turns out my 3mm should've been 5mm at the spine and 3mm elsewhere, and I'd been squaring the whole thing wrong because I never checked the square on my bench (it was out by a hair, enough to throw off a 9 inch board). I re-cut 14 boards last Saturday and every cover sat flush for the first time in 4 years. So what's your actual spine allowance and do you measure it or just trust the jig?