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Vacuum Bags

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Old 09-08-2012, 09:38 AM
  #1
LRFitch
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Default Vacuum Bags

Folks,

I have just assembled a vacuum bagging setup, and would like to use the system to sheet some balsa/foam wings and stabs for a pattern airplane I'm building. But I still need some bags to put the wings, etc. inside and seal. I know several composite suppliers sell bags, but I'd like to make my own if possible. Joe the Woodworker shows how to make them out of 300 mil vinyl. I don't think this is the stuff modelers use, so thought I'd ask and see what I can use and would be available in a small town. If you have a material and adhesive set you use, could you share your approaches?

Thanks ,
Larry Fitch
West Richland, WA
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Old 09-09-2012, 05:32 AM
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Default RE: Vacuum Bags

I use the thickest dropcloth plastic Lowe's sells and the cheapest white caulk to seal it off. When I skin the balsa to foam I use the same plastic between the balsa and foam shuck to keep any glue from pulling thru the wood and sticking the whole thing togeather.
When I do glass over the wing exterior I get some .005 thick clear plastic from an art store and use that for the finish barrier. I put some paper towel around the exterior to allow even pressure and give a weep area for the glue to go.
Works pretty good for me and is much cheaper than peel ply and custom bag material.
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Old 09-09-2012, 08:13 AM
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Default RE: Vacuum Bags

I'm with Vic, I use the same tarp material and calking. No need to let the calking dry either. Just remember to always use some type of breather from your vacuum nippel across the bag. If not you can easily end up with un-equal vacuum from one side of the bag to the other.
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Old 09-09-2012, 08:35 AM
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Default RE: Vacuum Bags

Gents,

Thanks for the responses. I take it you don't use a clear bag material, as all I can find at HD and Lowe's are white or black in color. Further for the caulking material do you mean a "silicone-type" material in a large tube that you dispense with a caulking gun? Will the caulk make a permanent seal on the bag. I was hoping to make a 4' X 3' bag or two permanently sealed on three sides that I could put the two wing halves in and seal shut with one of the temporary seal strips like I use on my smaller bags I bought from ACP for the skinny glider wings I have been bagging up until now.
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Old 09-09-2012, 11:11 AM
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Default RE: Vacuum Bags

Latex caulk works just fine. I don't get silicon anything next to something I am bonding. Think of your bags as throw away items. Use once and throw away. If you get into the habit of re-using them it will bite you sooner or later.
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Old 09-09-2012, 11:43 AM
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Default RE: Vacuum Bags

Yeah, sometimes I will use a bag more than once for a wing if everything cleans up well. But for tails and custom parts I only use it one time.

About the caulk, I use the absolute cheapest stuff I can buy. There is nothing permanent about the bag. It just needs to stop off air leaks till the glue kicks off after that it goes in the can. Usually I turn the bag over and let it dry and it falls off the bag. Don't worry about a special nipple to connect either, just build up a glob of caulk and set the line in it. The vacum will seal it off. Like SRT said running some kind of breather around the whole area is kind of important if you want to get an even squish.
When I do CF over a tail surface and want it to look good I use the .005 clear plastic with paper towel running right up the edge for a blotter. Then as the vacumn pulls down I help it along with a credit card thru the back to get the glue moving in the right direction.

It really is pretty simple considering the cool results you get.
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Old 09-09-2012, 12:36 PM
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Default RE: Vacuum Bags

Back in the day when I used to produce a lot of bagged wing I used the tube bags from ACP. I would attach the breather to the inside of the bag so I didn't have to fuss with it each cycle. I was often able to get 20 to 30 uses out of a single bag. You can see this setup with the attached breather in this very old video that I made: https://vimeo.com/2357551

I also use poly tubing for several application. You can get it in rolls in various thicknesses. I used the 4 mil for multi-use and the 1.5 mil for single use. I used an 24" impulse sealer to seal the ends and an ACP vacuum port through the bag. I would cut the bag longer than I needed and then cut one end just inside the seal with a scissors to open it. I could then reuse it by just sealing the open end again with the impulse sealer. The bag will get slightly shorter with each use.

You can also heat weld your own with poly drop cloth plastic using the technique shown in the video. This video shows it's use for bladder fabrication for molding but you can use the same technique to seal bags. You can go directly to minute 3 to see the sealing method. https://vimeo.com/35648020

If I'm bagging molds then I often use the caulk method. Wing molds can be rather heavy and difficult to slip into a tube style bag.

If you are doing vacuum infusion then the poly plastic and Stretchlon 200 is notorious for being slightly permeable and fouling the infusion. I'd recommend making your bag from Stretchlon 700 or 800 for infusion.


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Old 12-02-2012, 03:10 PM
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Default RE: Vacuum Bags


Quote:
ORIGINAL: vicman

I use the thickest dropcloth plastic Lowe's sells and the cheapest white caulk to seal it off. When I skin the balsa to foam I use the same plastic between the balsa and foam shuck to keep any glue from pulling thru the wood and sticking the whole thing togeather.
When I do glass over the wing exterior I get some .005 thick clear plastic from an art store and use that for the finish barrier. I put some paper towel around the exterior to allow even pressure and give a weep area for the glue to go.
Works pretty good for me and is much cheaper than peel ply and custom bag material.
Im going to try some vacuum bagging in the near future. Are you saying the paper towel goes between the bag and wing surfaces. If so how do you get the paper towel off the wing when dry. I know peal ply is made to peel away from the glassed wing. Do you sand the paper towel away?
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Old 12-02-2012, 03:39 PM
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Default RE: Vacuum Bags

The idea is to put a thin price of plastic sheet over the balsa sheeting ( I use 2 mil mylar ) then the paper towel. This way any adhisive that gets pulled through the sheeting will not get to the paper towel. Peel ply could also be used but adds to the cost of the project.
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Old 12-02-2012, 04:01 PM
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Default RE: Vacuum Bags

And the same is applied when doing glass over the wing exterior,is this correct. One other question can I glass a balsa built up wing on both sides and place it in a vacuum bag without crushing it or warping it when its placed under vacuum?
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Old 12-02-2012, 04:12 PM
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Default RE: Vacuum Bags

No, it will crush. When glassing a built up sheeted wing just apply the cloth and resin then blot out the excess resin with paper towel or you could get creative and lay down a sheet of peel ply. With the peel ply method you would squeege it down flat and then go over it with a hair dryer. This will wick the excess resin up into the peel ply.
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Old 12-02-2012, 04:36 PM
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Default RE: Vacuum Bags

Ok thanks glad I asked, would have sucked to try it and find my wing flat as a pancake. So basically I could do a solid surface like a fin or rudder a solid stab or a foam wing that was sheeted or glassed could be put in the saddle and done using mylar and paper towel to wick up the excess epoxy.
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Old 12-02-2012, 04:41 PM
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Default RE: Vacuum Bags

If you are glassing the exterior of a solid peice or a foam wing using a vacuum bag then the process would be to glass the part add a sheet or peel ply, breather and then in the bag it goes.
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Old 12-02-2012, 05:12 PM
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Ok thanks again
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Old 12-05-2012, 09:21 AM
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Default RE: Vacuum Bags

One thing I found useful, if you've ever had your house tented for termites - they used to give out "nylofume" bags to put your belongings in. I had some extra of these and they work great for "small" parts together with the ACP tube bag clips. bags are like 2'x3' and sealed at one end.
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Old 12-07-2012, 05:50 PM
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Default RE: Vacuum Bags

Quote:
Are you saying the paper towel goes between the bag and wing surfaces. If so how do you get the paper towel off the wing when dry.
Sorry it took this long to reply, I've been ooc.
Hopefully this picture describes what I was trying to say.
I have tried putting paper towel over the thin plastic (others use mylar) to get an even breathing layer only to end up with an imprint of the towel on my parts. Now I just do as the picture shows and it works just fine. The finish is very smooth.
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Old 12-08-2012, 12:58 AM
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Default RE: Vacuum Bags

I've use the clear plastic film used for weather proofing your doorwall. It's 8 mil thick and I found it at Menards. You need mastic tape (which is kind of like a putty tape) which I bought at a fiberglass shop. I built a bag big enough for a homemade windsurfer in.

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Old 12-08-2012, 09:10 PM
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Default RE: Vacuum Bags

I think the plastic film material is actually vynl

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Old 12-08-2012, 09:53 PM
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Default RE: Vacuum Bags

Dunno, I get it from a craft store. It works extremely well and gives a great finish.
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Old 12-21-2012, 10:48 AM
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Default RE: Vacuum Bags


Quote:
ORIGINAL: wyowindworks

Back in the day when I used to produce a lot of bagged wing I used the tube bags from ACP. I would attach the breather to the inside of the bag so I didn't have to fuss with it each cycle. I was often able to get 20 to 30 uses out of a single bag. You can see this setup with the attached breather in this very old video that I made: https://vimeo.com/2357551

I also use poly tubing for several application. You can get it in rolls in various thicknesses. I used the 4 mil for multi-use and the 1.5 mil for single use. I used an 24'' impulse sealer to seal the ends and an ACP vacuum port through the bag. I would cut the bag longer than I needed and then cut one end just inside the seal with a scissors to open it. I could then reuse it by just sealing the open end again with the impulse sealer. The bag will get slightly shorter with each use.

You can also heat weld your own with poly drop cloth plastic using the technique shown in the video. This video shows it's use for bladder fabrication for molding but you can use the same technique to seal bags. You can go directly to minute 3 to see the sealing method. https://vimeo.com/35648020

If I'm bagging molds then I often use the caulk method. Wing molds can be rather heavy and difficult to slip into a tube style bag.

If you are doing vacuum infusion then the poly plastic and Stretchlon 200 is notorious for being slightly permeable and fouling the infusion. I'd recommend making your bag from Stretchlon 700 or 800 for infusion.


Thanks for that. I've been trying to come up with a way to make a bladder for some time now. I can see this as a good method to possibly get glass tape into the back end of the fiberglass planes without using a thick mixture of silica and epoxy.

Tim
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