Photo: My trial-and-error hollow cube blocks, pinned to my draperies.
I'm working on my One Block Wonder quilt, and since I am so anxious to get started on this right away, I don't at the moment have patience to order and wait for the second book (OBW Encore) that tells the details of how to make the hollow cube. I played around with my scraps for a few hours (actually a lot of hours - buying the book would have been better, but I would have either had to take a trip into town or wait almost a week for it to arrive in the mail) -- and I finally solved most of the issues. Hurrah!
I made three trial blocks. The very first one, not pictured, was so bad that it now resides in my wastebasket. The one on the above left, which I thought I had so carefully measured, was too large, but the last one was just right. It basically involves cutting an inch off one side of the triangles and sewing inch strips back on. However, I plan to get the book anyway, because it has lots of variations, and probably has streamlined the process better than I've been able to figure out.
One thing I learned about sewing the OBW strips together is that the little eartags of fabric are wonderful for matching up seams. Match the ears, and voila! the seams are matched. No pinning required -- a good thing, since all my quilt pins disappeared when I mopped and shined my floor. That little mystery has lasted five days so far.