During your school days, did you ever have standardized tests that featured drawings of various, increasingly complex, two dimensional shapes from which you were to determine what the shape would look like when folded into a three dimensional vessel? I liked working out these questions, but was never convinced they measured anything of significance. Regardless of their value, designing sewn fabric boxes is giving me flashbacks.
For the third construction method I'm testing, I decided to work it out with paper models. I couldn't quite mentally grip what each dimension of the flat shape would become in the finished box. (Let's be generous and chalk up this failure of imagination to decades away from standardized testing? Thanks.)
Once I made a model, I understood the construction, but I still didn't have a formula to work out how the dimensions of the starting flat pieces contributed to the finished dimensions of the box. So I cut the box apart, labelled each dimension, reassembled it, measured it, and worked out a formula.
This is pretty much what it comes down to. But, oh! Seam allowances! They threw me for a loop. Had to make another model to figure that out. If you can make sense of my notations above, the seam allowances calculated are for a box with a raw (not hemmed) top edge. For a hemmed opening, add 2z to the y dimension. And, to be perfectly accurate, 2x = perimeter of box opening (a 3 inch square box will have an opening perimeter of 12 inches).
After working these up with fabric, and assuming they work, how about a tutorial?
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