Vacuum bagging without a bag

[Jurgen]

Time to fix that broken boom, but not necessary to put it in a big bag.
Just rob that kitchen, it just takes bakery paper, paper kitchen towel and this very thin food film (the sticky stuff to put the sandwiches in).

I first aligned the fuse perfectly & temporary glue.
Time to glue the fabric under vacuum:
- rolled the whetted kevlar layer around the fuselage breaking line;
- rolled a piece of perforated (used a thick needle for that) bakery paper around the kevlar, it bounds zero to epoxy;
- rolled thick layer of kitchen towel around the brown paper to absorb the squeezed epoxy coming trough the perforations of the bakery paper.
- rolled some vacuum towel around for distribution of the vacuum;
- embedded the whole bunch in this plastic for storing food in. I used 2 layers as this foil is so darn weak and easy to punch trough. 2 layers handle better and are ideal strength.

The plastic has the tendency to stick on itself like hell and can be wrapped around very easily, only a few tapes needed around the vacuum tube and fuse to make the set 100% air closed. No silicone and pressure nipples needed.

Tomorrow I'll open the kitchen experiment to examine the result :)
Jurgen.

[Jurgen]

Nice:
the perforated bakery paper did a wonderful job, lots of epoxy squeezed trough into the paper towels

not so nice:
although I wrapped the kevlar close around the boom, some squeezing bulges did form. If I hit them flat then the tissue will be harmed there. But there's no choice, an extra thin glass layer will cover the total.

[target]

I still think your idea has a lot of merit, even though you didn't get perfect results.
Great Idea!

Target

[Jurgen]

Thx Target

because there's no hassle with silicone you better have some try setup first without epoxy-ed layer, just to see if things work out.

Over the break I had 1 layer of carbon strips, later the kevlar mentioned before, later the glass. I dare to hope this is strong enuff.

At the end realised that for such a small job the vacuum might be skipped if one is careful with applied epoxy.

But it was fun to experiment. It was the first time I used my scratch build vacuum system. In front an industrial explosion proof pressure switch, large and heavy as hell :) but for free. It was actually an overpressure switch (copper connection) but I managed a nipple at the other side of the membrane so it became an under pressure switch. Now it actually works too well as the hysteresis (on-off difference) is quite small.
Jurgen.

[target]

It looks like your vacuum system could use a reservoir if it doesn't already have one.

T

[Jurgen]

Yes it has, you see alot of connections on my fridge pump, one of them goes to a metal 20 liter vessel (670 oz.)
I tried to do with and without the tank to observe the difference. There was difference, but less than I expected although it is a big vessel.
Jurgen.

[MarkusN]

What I did in a similar situation: added a time relay behind the pressure switch. As soon as the switch kicked in, the pump would run for the time specified on the relay.

That took care of the hysteresis issue.

[Jurgen]

Markus, great minds think the same ;)
I searched for some time relay for free but didn't found one so far, new prices are rather expensive, and if money has to go over the desk then I might prefer a serious circuit like this one (at the end of the page):
http://pierre.rondel.free.fr/
We'll see what comes out of this.
Jurgen.