Thanks guys. The power of the web, we can share these ideas in an instant - I still find it amazing
I source the ply from a local timber supplier, Turners Timber in Fyswick. I believe they get it from BrimsPly in Sydney. They call it "bending ply" and is 1.8mm thick 3 ply Hoop Pine, comes in 4X8 size sheets. So with 3 layers of ply you get a light weight UTA with 9 laminations and less than 6mm thick
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Here is a link to Dave Gaults website where he describes the ply tube fabrication process much better than I could. This is where I got the idea from, thanks Dave
http://users.tpg.com.au/users/daveg/Tube.html
I found a cutoff from the 8" mirror box and the attached images show how the Jarrah corner pieces fit. I also sanded one corner so you can see the colour difference. There are additional bracing pieces glued on the inside to provide additional rigidity and strength. I did make a couple of test pieces first. When subject to the breaking test, the glue joins remained intact and the wood gave way.
Mark, this is the Upper Tube Assembly - tube component, yes, the diagonal cage. Re overlap there are 3 thin layers of plywood and the joins are placed about 120 degrees apart.