#rightside-out

The solution to this sewing/topology puzzle (”How do I sew this inside-out, so that when I turn it rightside-out, it’s a bag?”).  

Teaching myself to sew is recalling my topology education!  How do I sew this together inside-out (so that the raw edges are hidden), and then turn it rightside-out to get a functional bag?  

I figured out how to do it yesterday--and then forgot, so I had to figure it out again.  But this time, I was smart and recorded the solution!  

This video is to introduce the problem.  I’ll post another one later, with a solution. 

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Where we're at: First, I sewed (essentially) two equally sized rectangles of fabric together to make a cylinder. Now I need to turn the cylinder into something isomorphic to a ball, but where one hemisphere is pressed into the other (to be concave), like a double-walled bowl.  I also need the right sides facing out by the end.  

A solution I rejected: sew all around the exterior of the fabric, but leave a gap; then pull the fabric rightside-out through the gap. This creates a large rectangle with all edges finished (ie: no raw edges exposed).  But then a new problem arises: because the raw edges are hidden, there isn't enough fabric available to make a strong stitch to hold the finished edges togther. So I don't want to use this method.

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There is an elegant solution that involves three seams (and one gap separating two of those seams). 

How did I do it?? 

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