[NSRCA-discussion] Vacuum Bagging - More Info

[Robert Campbell]

I've just rejoined the discussion list and noticed a great discussion on vacuum bagging.  I also have the low cost ACP vacuum bagging system and I love it.  I've done wings for a couple of sport models and a few EDF kits and am very happy with the results.

Someone posted that the ACP system draws a 3 psi vacuum.  That seems about right.  If you do the math for a 200 sq in wing panel, that's equal to stacking 600 lbs on top of your wings!  And, the pressure is perfectly distributed, ensuring a solid bond between the skin and the core.

One trick I started doing a few years ago is using polyurethane glue (Gorilla or Elmers Pro Bond) instead of epoxy.  My technique is to edge sand the skin sheets and then tape then together on the outside of the skin.  I then apply the glue to the inside of the skin and take an old credit card to squegee off the excess.  I leave just enough glue to make the skin appear damp.  I then place the skins on the core, wrap with breather cloth and insert into the bag.  I then place the assembly back into the cradles and add some weight (2 large books are enough) to stabilize the assembly.  Once I'm happy with the alignment of the cradles, skins, and cores, I start the pump and let it run 18 to 24 hours.  The next evening I have a very light, perfectly skinned wing.  The bond is extremely strong because during the curing process, the glue soaks into the skins and it foams and works its way down into the core.  The glue also seeps into the butt joints of the skins and bonds them with virtually no ridges on the outsides of the skins.

I've become a firm believer in vacuum bagging.


Rob
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