Vacuum Bagging

I've recently had an epiphany of sorts related to vacuum bagging. Ever curious since I heard the Cozy Girrls were doing something they called Lo-Vac, I looked around on the internet and educated myself on how it was done. Following that, I shopped around for a system. I settled on a unit/kit from Aerospace Composite Products. I have since done my landing brake and elevator bottom skins with it and I am hooked. It works great. No bubbles, no wrinkles, less stress about recesses and corners, quicker layups, lighter layups, more strength, better glass to resin ratio, the list goes on. Check out the pictures and text below, it's quick lesson in how it's done.
	This is the pump assembly I purchased from Aerospace Composite Products. While made for the hobby/model industry, it is a very nice system. I comes with a pump rate for continuous operation, an vacuum pressure setting valve and a reservoir. The reservoir prevents resin from getting into the pump and, if you have a good envelope set up that doesn't leak much, can keep the pump from running at all for the duration of the cure. You also get tubing, clamps, power cord, etc. I'd recommend this to anyone considering doing any bagging.
	The kit I bought also comes with a device they call the EZ-Vac connector. It is made up of four parts, the connector itself, with small channels milled into it to allow the air to pass through even when the bag is tight, a washer for inside the bag, a ridged washer for outside the bag and a nut to hold the pieces together. You slip the connector with the black washer on it into a 3/16" or so hole in the bag before you close the end. Then add the ridged washer and nut from the outside and tighten.
	The kit also came with some bagging material, 9' of 18" wide nylon specifically, and two Quick Lock seals. The quick locks are used by placing the bagging material between them then snapping the inside piece into the outside piece.
	The bagging material is open on either end but the edges are sealed. You can buy larger bags and more of it. For the record, I have done several layups in this bag with these clips. The only parts you HAVE to throw away (people complain about the consumables prices for vacuum bagging material) is the peel ply and paper towels. Since most of you are peel plying anyway, the only added consumable cost is the paper towels, and they're not very expensive!
	To make the vacuum bagging envelope, start but putting one Quick Lock seal on one end of your envelope. This is just a simulation for the picture, of course, you would not get a very big part into this envelope. You can see the roll of vacuum bag to the left of the seal that's on the bag. I just unroll as much as I need then put on the seal at the right spot.
	You then add your part, some paper towels and the EZ-Vac connector. I have been using two layers of peel ply, followed by two layers of paper towel. I use enough paper towels to reach the connector to serve as an air channel. Keep the connector a good distance away from the layup to prevent epoxy from wicking through the peel ply and into the connector or vacuum tubing.
	Add the other quick lock seal and you're ready to pull a vacuum. I usually have to tighten the nut on the connector with pliers, but, be careful not to rip the bag or over-tighten and stretch the bag out from under the washers and cause a leak. Occasionally, the hole for the connector gets damaged a bit. If you put it close to the end of the bag, like this, and it does get damaged or distressed enough to not be able to get a good seal, you can cut off a couple of inches of bag for the next layup. That way, you haven't ruined the whole bag and can still re-use it. Sure, it's a bit shorter, but, that's better than buying a new bag.
	Now hook up the vacuum pump and turn it on. Sometimes you have to watch the vacuum get pulled to 1) be sure your envelope is sealed (if the vacuum gauge never shows a vacuum you have a leak) and 2) make sure the bag is flattening the way you want it with no big wrinkles in a spot you don't want them. If this happens, I turn off the pump, take the tubing off of the connector or open one of the seals to let air bag in, re-adjust the bag then try to apply the vacuum again. If you have a good envelope, the vacuum pump will do its magic in less than a minute and then the vacuum will be maintained. I have even gone so far with some layups as to unplug the pump. I simply check the vacuum gauge and if it's still showing good vacuum I know there's no need for the pump to run.
If the steps above don't explain the vacuum bagging process well enough for you, follow this link. That will take you to the Top Skin section of the elevator construction. I did a photo series including just about every step of the vacuum bagging process.