Homemade Vacuum Bagging
After searching the internet for tips on using vacuum bagging in boat building, I decided to give it a try. I found a discarded refrigerator out four-wheeling one day, so I liberated the vacuum pump from it.
The wiring wasn't obvious, so I had to do some testing to get it right and to make sure the outer shell of the vacuum pump wasn't 120vac HOT. :) If you are going to do the same thing, take it to a professional electrician otherwise you are gambling with your life.
The pump sits on rubber feet, and is very quiet. When bagging this paddle the pump got up to 140 degrees F while pulling the vacuum after about 2 hours. I might have to install a pressure switch to cycle the pump in order to keep it cool.
These bags are soda syrup bags. Soda syrup bags are rather inexpensive if you get them used from a fast food joint or almost any place that serves fountain soda drinks they are free. This bag is actually 2 bags in one. The outer bag seems to be mylar, and the inner bag some other type of plastic. The bag also has a corrugated piece of plastic that runs the length of the bag that allows the syrup to be sucked out. It also works to get air out of the bag when a vacuum is pulled in the bag. These two bags were rinsed out, and inflated. They have held this pressure for a little over 3 days. They are pretty tough, and I think can be used as flotation bags as well as vacuum bags. .
Soda syrup bags have a valve that has to be removed in order to clean it out. Once out, the valve needs to be disabled. After cleaning the disabled valve is reinserted in the bag. The valve itself has threads on the outside. It just so happens a cap from a 2 liter soda bottle screws on those threads. To attach the vacuum pump to the bag, I drilled a 1/2" hole in a 2 liter soda bottle cap, and pulled an automobile tire valve stem into the hole. Once the Schrader valve is removed from the valve stem, a vacuum can be pulled in the bag.
Here is a paddle blade fiberglassed, bagged, and under vacuum. The outer bag is wrinkled, but the inner bag is sucked flush to the paddle.
I cut the bottom out of the bag so I could put it over the blade of the paddle. I ran a band of packing tape around the edge of the outer bag to reinforce the open end of the bag. Then I wrapped the shaft of the paddle with plastic wrap. Once the blade was fiberglassed I put it in the bag, and using packing tape sealed the open end of the bag and around the shaft.
Here is the paddle in the bag with a vacuum on it.
Here is the pump running with 23 inches of mercury, that's about 11 psi. To get the same pressure with weights, I'd have to pile about 1700 lbs of stuff on top of the blade.
When I recovered this pump the exhaust was broken off flush to the cannister. I was able to put a plastic adapter in the hole, and attached the clear hose to that. Oil exhausts along with air, and I didn't want to lose the oil, or get it all over everything. The loop traps the oil, or at least most of it, and the tissue paper loosely stuffed in the end traps some of the aerosol oil. I've sewn an "X" in the end of the exhaust hose with safety wire to keep the tissue paper from being blown out.
This is a shot edge on to the paddle. It's kind of hard to see, but the bottom of the bag is pulled up against the blade too. Ya gotta love how vacuum works. :)
Here is the the paddle after 5 hours in the bag. It looks like the inner bag did have some wrinkles in it.
The epoxy did not stick to the bag. The bag pulled off quite easily.
My technique leaves a lot to be desired. There are places where the epoxy filled the wrinkles of the bag. I hope to improve it for the next blade.
THE NEXT BLADE
After seeing my first blade, Chris Ostlind suggested I try a peel ply and some "Monkey Fur" as a breather material. The combination of the two ensures even pressure and draws off excess resin. So I decided to try it. Well not exactly, I had some stuff in my Fiberglass box that I think I was told long ago was peel ply, and although I didn't have any "Monkey Fur" but I did have some polyester pillow stuffing. So what the heck.
Here is the second blade bagged up. After wetting the blade applying and impregnating the fiberglass I wrapped in peel ply shoved the whole mess in to the bag and jammed the polyester pillow filling in. I didn't get the "Monkey Fur" stuffed all the way in the bag, but it looks like it's working
After removing the bag, I pulled back a corner of the peel ply. I've pulled most of the polyester fill off. The rest you see here is stuck to the peel ply by the epoxy being wicked up through the peel ply.
Using the peel ply and breather method produced no wrinkles, but the fiberglass seems a little dry in a couple of places. I think that's because I didn't use enough fiberglass to start with, not as a result of the process.
There is one more paddle to go, so that's two more blades to play with. For the next one, I'll use the two layer bag with out peel ply. I'll put the polyester fill between the bags, and pull the vacuum on both. The excess resin won't get wicked out, but I should get fewer wrinkles than the first attempt.