Since the ribs have been bent to the proper shape and edges trimmed to the correct angles, the lute back can be assembled with tape to hold the ribs together during gluing.
Here you can see several ribs being glued and taped together. The foamcore template is useful to have something to hold the ribs while the glue dries
Once you get several ribs glued together, it's easier to just continue assemble "free-form" withour the template. As each rib gets added, the bowl becomes quite stiff.
Oh what a messy glue job :)
After a little cleanup you can add the reinforcing paper strips, glue in the neck block and add the bottom reinforcement.
Go here to see how to make the neck block.
Go here to see how to add the bottom reinforcement.