Well it is done. A quick test run proved it would do the job but as grumpy expected it was a bit flexy but more so in the middle. The tube needs strengthening for long term durability.
[Linked Image]
[Linked Image]
I believed it was strong enough to cut the 5 or 6 branches I needed to cut and it has proved so.
Having finished this now I reckon the best long term option would be to use tbe powerhead and chainsaw attachment separated from their respective tubes and connect a single piece larger diameter tube between them with a straight single piece driveshaft running in the tube.