The aluminium tube used to make the carbon wing joiner rod took a lot longer to dissolve in caustic soda than I had thought. Thanks Mike for the suggestion to put Dremel grooves on each side almost right though - even then it took two days to get through the grooves!
The calculation I used was 40% carbon 60% resin (very pessimistic) and when wet out it was way too easy to pull through the tube. I increased the carbon to 50% by area and it was much tighter so I left it at that.
Clearly not quite enough carbon as you can see - next time it's 60% carbon and if that isn't a really tight fit then add a bit more!
Just to make it a full house the motor I installed to power my vacuum pump had a faulty nameplate. It says it's S1 duty rated, i.e. continuous running but this was incorrect leading to massive heat build up and bad smells! It was set to run for half an hour then wait an hour as the vacuum regulator switch is giving problems. (It was not pressing foam but a wing mould so the very high vacuum was ok).
Oh well, the wing is next, just after the vacuum pump is re-built and a quick trip to the Berg next week!
Anyone know where to get a proper vacuum switch – Festo’s one is nearly R1000 while Joewoodworker.com’s sells one for only $25 but won’t ship to South Africa!?