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Wednesday, July 2, 2008

Time to do it again!

In the time honoured Jart tradition of learning new and fun stuff - sometimes you have to do it again!

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’s sells one for only $25 but won’t ship to South Africa!?


Evan Shaw said...

Never nice to have problems, but it's how we learn. Hope it works out next time.
Maybe this will help!
After the carbon has been pulled through and cured, try heating the Alli tube up in an over (maybe 100 degrees max) and then quelching in cold water to break the bond. Then push or tap the carbon out. I have managed to make several joiners that way with thick walled Alli tube. Never with thinned walled though. Call me if you need help.
Good luck

Evan Shaw said...

I made my vacuum switch from a vacuum advance and retard thingy from a car distributor and a micro switch. I think it was from an old VW Passat. I'll see if I have a photo somewhere, so I can post it!
Cost? a few bucks and lots of clambering around a scrap yard!