Could this be the cause?
I used breather top and bottom.
Phil Barnes wrote:
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The breather is in contact with the lower foam
bed. The core and mylars lie in the lower bed and so are not in
contact with any previously used breather.
As you know from my video, I place the cores in the mylars, then the mylars go inside a release film/breather envelope, this then goes in the bag. The beds are outside the bag. I can't tell for sure from your post, but it sounds as if you might be putting the beds inside the bag or perhaps are not using the top bed at all. If you are not using the top bed and are placing weights directly on top of the vac bag, this could cause dents to appear in the wing. Many years ago I tried putting bricks directly on top of the vac bag without using the top foam bed. The weight of the brick and the uneven surface of the brick caused dents in the top of the wings.
If you continue to have mysterious problems then I would recommend that you follow the procedures in the video as closely as you can. If that produces good results then you can start changing one thing at a time if you want to go back to your own methods. It sounds as if you are doing quite a few things differently from my methods. One or more of those things are producing unexpected and unwanted results. You likely are encountering a problem which I have never encountered since I have never used those methods.
I never get any of these defects in glassed balsa parts, even with very
light, soft balsa.
This makes me think about something that melts the foam. I do know that unmixed epoxy (or more likely, the hardener) will melt foam. Could there be a chance that you are not mixing the epoxy thoroughly? Little lines of unmixed epoxy perhaps melt little trenches in the foam core.
These defects sometimes appear just over the foam,is
sometimes over the foam and the uni. Since the glass surface in the 'dent'
smooth, well wet-out and well bonded to the core, it's getting someconsolidation
pressure in the bag. That's why I suspect trapped air or volatiles of some
sort.
I'm not sure I totally understand this but this does not sound like melted foam is the problem. It does sound like trapped air although I have never personally experienced a "trapped air" problem other than the lifted paint problem that I described earlier. Once again I would suggest following my procedures from the video more closely. I only use a squeegee for layups on layups that only use glass. I use a foam roller to spread epoxy on all carbon and Kevlar layups.
Perhaps I'm just crushing the foam with too much pressure for 150?
Too much vacuum on softer foams can cause the entire core to get compressed a few thousandths of an inch. It can also cause tips or leading edges to get crushed in odd ways when the mylar extends past the foam and cannot conform readily to the curves. There is no reason suspect excess vacuum as a cause for thin lines or depressions in the center areas of the core.
Phil
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