The sides are just under 2mm thick (they're not structural, but sides that thick are tough enough to keep an acoustic guitar in one piece, and any way, anything over 2mm is tough to bend - I use a hot pipe).
The back is another matter. What kind of fool would plan to make a 12-piece back, you ask? This kind obviously!
Partly aesthetics - it's a wide circle, and it would look pretty dull if it were completely plain.
And partly available wood - I could cut a two-piece back with the join down the centreline, but it's hard work resawing a 7 inch wide plank, and would still look fairly dull.
So instead I cut 12 triangles, each of which is slightly over-size.
I glue three together, glueing them face down to some stout printer paper, to make quarter backs. The joints are end grain to end grain, so they are very weak. The paper is pretty good as a reinforcement, and will anyway be removed later.
Then I trim one side to make the whole thing closer to a right angle, and glue to a second quarter back to make a half back.
You will see that each quarter is still a little more than 90 degrees, but I'll plane the open side back to a straight line before joining the half backs. The final result won't have exactly equal segments, but I'm hoping that won't be noticeable!
Here's the visible outside of the back once it's assembled:
The inside is reinforced with brown paper (although it looks grey in this pic).
Some segments are dangerously thin at the rim, so I'll laminate some mahogany inside before I glue up, to give me a reasonably even rim. Then the final challenge will be to sand the back without sanding through the thinnest parts! Livin' on the edge, me.
And once shiny, it looks pretty much OK:
