I tried this to make a sketchbook from watercolor paper, and I only used 3 signatures with 2 pages each – because that was all the watercolor paper I had left. Once I've filled this, I'm sure I'll make more! I might also do some sketchbooks with different kinds of paper.
I did another sketchbook in A5 size, 8 signatures with 8 sheets each. The weight of the sketchbook or tension of the binding was apparently too much for the cover to handle – the back cover tore around the holes in several places.
I think I'm going to either use much sturdier cardstock for the covers of future sketchbooks in this size – or use a different method to make a harcover with coverboard instead of cardstock. I'm thinking about repairing the cover around the holes with the same pink duct tape I used for the stripe on the cover.