Recently I found myself looking for ways to reduce the weight of rocket components such as fins and centering rings without losing strength. The solution appearred to be foam cored composite materials but all of the literature I read indicated the need for a complicated vacumm setup; something that I neither wanted or could afford. After looking at a number of other websites I decided to purchase a Food Saver at a local Kohls store (it was on sale). The Food Saver is intended for vacumm sealing of foods to extend the period of freshness. The one I purchased came with rolls of bag material in both 8" and 11". You can also purchase the bags pre-made but due to the odd sizes that we tend to work with it seemed best to buy the rolls and create the bags as needed.
Creating a Part
I will detail the process of creating a fin; the process is typical of most parts you might make. The first step is to create the core. For lightweight structure I use 1/4" foamboard as it is very light and the paper skin makes bonding easy. When I cut out a component like a fin I bevel the edges using a matt knife. This gives me 45' angles and allows the edges of the fiberglass to seal well. On parts like centering rings this isn't necessary because the ring will be bonded to the tube.
After cutting out the core I will cut a piece of cloth, usually fiberglass or carbon fiber, that is a little more than twice as large as the object to be made. This helps create a good edge. Place the piece of cut cloth on a larger piece of polyethlene film (like the stuff the home stores sell) so you can apply the resin. I use epoxy resins from either West Systems or Mr. Fiberglass but there are a number of other choices around. I use a slow epoxy to allow a longer than normal working time. Apply the epoxy a little heavy to ensure you get a good bond.
Place the foam core in the middle of the wetted cloth and then fold the polyethlene film over the core. This way
you don't have to touch the wet cloth directly and it is easy to squeegee out the air. Make sure the core is centered on the cloth and that as
much air as possible is squeezed out. The next step is to apply the peel ply and the breather fabric. You will need a piece of peel ply cut that
is slightly larger than the fiberglass cloth and a piece of breather that is slightly larger than the peel ply.
Peel back the top layer of the
polyethlene film to expose the top half of the laminate. Lay the peel ply on top of the wet cloth. Match the edges with a slight overlap so that
when you are finished you will have a little ectra peel ply all around. Now flip the part over, peel off the remaining polyethlene film and finished
wrapping the peel ply around the core and the cloth.
Once you complete this step you should have a part that is not wet on the outside. This makes it much easier to handle. One quick note here: when you put on your safety gloves put on two sets of gloves. That way if you accidently get resin on a glove you can quickly remove the glove and not be without protection. Anyway, lay the peel ply coated part inside the breather fabric. You now have a sandwich of materials ready for the vacumm.
Usually when I am going to make some parts with the Food Saver I plan to make a number of parts at one time and I make all of the right size bags before I start. You will need a bag that is a couple inches longer than the part. I usually buy the Food Saver bags as a roll. Another option is to buy premade bags. Whatever method you choose to use is fine, just make sure you have enough of the right size bags plus a couple of spares available. By available I mean out in the open and easy to get to. The wife loves it when I get epoxy resin on a cabinet door because I was one bag short! The next step is to slip the layed up part into the vacumm bag. Work slow and ease the part into the bag ensuring that the layers stayed straight and smooth. A wrinkle here can mean more sanding later.
Now all you have to do is slip the open edge of the bag into the Food Saver, push down on the lid, and hit the button. I find it is helpful to have a couple of extra sets of hands during this part, particularly a set of clean hands. Epoxy resin on the Food Saver is as big a hit as the epoxy on the kitchen cabinet with the wife. Now just store the part where it can cure flat. On really thin parts I will place them between sheets of glass to keep them smooth and flat. Once the resin has cured you can cut open the bag with a utility knife and peel off the peel ply exposing the finished part. Don't be in too big of a hurry or the edges will come apart and ruin the piece.
When working with epoxy resin it is very important to protect yourself from contact with the resin. Long term exposure will cause bad dermatitis. I know this from experience. When I was young I built a large boat with West System Epoxy and rarely wore gloves. Now any unprotected contact with epoxy resin causes a bad painful rash that takes days to go away. Protect and Enjoy!