Simple Vacuum Bagging

I have been making small fiberglass parts for a while now and I find that often the wet glass does not want to lay down properly around the curves of my moulds.

I was shying away from vacuum bagging due to the complexity of all the supplies needed if using parts from Aircraft Spruce or other fiberglass supply places.

Eventualy I decided that I need to make this work one way or another so I just ordered a small vacuum pump from Surplus Center and a large box of thin garbage bags. (thin bags contour and stretch better)

In this example project I am building fairing covers to close off the air conditioner condenser air inlet and outlet on the bottom of the airplane for use in the winter time and also to use as a speed test to see how much speed I am loosing due to inlet/outlet drag.

Here is the drawing of the external shape that I need.



Tracing it onto 1/4" Foam. This is the thickness that I need to clear the fins on the skin transition louvers.


Tapered the ends by sandding to make the shape I need.



Glued to a piece of smooth wood to make the plug. I am making the plug and will then make a mould to use to make the final 2 parts.



Mould smoothed up by smearing with micro and sanding. sanding. sanding...



First layer of glass. I used a very thin layer of glass here to help make a smooth surface on the mould



You can see in valleys of the plug that the glass does not want to lay down very well. This is the reason for vacuum bagging.



Another layer of glass



This is a thick layer of glass strand mat that I am using only on the mould for rigidity. The final parts will not have this layer.

This is a piece of regular aircraft fabric the same thing we use for "peel ply". Think of this as a lyer seperating the epoxy from the absorber.

One of the reasons for vacuum bagging is to draw out as much of reisin form the part as possible to reduce weight. We use this layer as a seperator between the riesin and the absorber. More on that latter.



Here is the abrorber. I just use cheap paper towels.



Now we want to hook the hose up inside the bag but we dont want it to get stoped up by the garbage bag sucking into it so just use a small piece of papertowel in the end of the hose and set this on the absorber. Think of the little piece of paper towl as a channel for the air to travel through as the bag closes in around the part.



Cheap little pump I bought.



Here the pump has just been started.



You can see that the bag is doing its job and pulling the glass parts up tight against the plug.



Here I am pulling the absorber (paper towels) and the peel ply layer off of the part. this was after about 8 hr of cure time.



Here is the mould.



Now the mould is sprayed with PVA as a release agent and ready to start the actual part layup.



Here is the first layer of glass used for the part. Again I used a very thin layer of glass first to help make the surface irregularities smaller so there is less finish work. Then I put down a layer of thicker glass followed by these strips of glass to thicken the area that will have the attachment screws.

Covered the strips with a final layer of medium thickness glass.


Again a layer of peel ply and the the paper towels and ready to bag.





Now the layers of the part are beeing bagged against the mould.



Here is the part fresh from the mould. Ready for sanding and filling pin holes then primer and paint.





This project was used as a deminstration of vacuum bagging. On a part this small most of the time I would just use the plug to make the part and then finish the rough side but by going the extra mile and makeing the mould you can have a lot smoother part when finishd with less finish work.

Excellent description of a simple way to do this.

Dave

Simple vacuum bagging

Fantastic series of photos and description. Its easy and nothing to be afraid of.

The time spent setting up the materials in advance is more than made up for by the lack of frustration during cloth wet-out if you didn't bag it, and by the higher quality parts.

We use polyester quilt batting for the absorber.

Also, the peel ply must be fine-weave polyester fabric. Epoxy doesn't bond to polyester. Go to a yardage store and buy the cheapest interfacing material that is polyester.

One added tip. In between the peel ply and the absorber, we use a "perf-ply" which is porous to allow resin through, but does not allow the resin-saturated absorber to get bonded to the peel ply. This makes everything easier to strip off the part. We make our own perf-ply by taking a very light-weight polyethylene drop cloth and, while it is still folded up in its package, we drill 1/8" holes through it on a 1" grid. (note, hole spacing is not critical, just eye-ball a reasonable grid of holes) Because it is all folded up, you are making many holes with each drilled hole. Then unfold the drop cloth and you have a big sheet of perf-ply with holes on 1" spacing. cut out a piece to cover your part.

Mold lets you make more than one!

Wesael said:

t by going the extra mile and makeing the mould you can have a lot smoother part when finishd with less finish work.

Click to expand...

Also, you can make more than one! Its worth the time investment as soon as your friend wants one too, or you goof the part up and need another one, or....

Excellent example.. Thank you sir for taking the time