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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: YEMX on December 11, 2020, 02:49:57 PM

Title: Vacuum Bagging
Post by: YEMX on December 11, 2020, 02:49:57 PM
Not sure where else to put this- Mods, feel free to move if needed.

I'd like to discuss vacuum bagging- not vacuum infusion.  Just simple vacuum bagging so I can get better results with my foam core stocks...  I want to use the bag to hold the fiberglass tight to the core, so I don't get bubbles and as an added bonus, possibly less finishing work.  I'm more concerned with less bubbles. 

The idea in my head is to simply have a stock with a peel ply against the stock with a breather layer on top of the peel ply, on both sides of the stock, then put it into a vacuum bag, and turn on the vacuum pump to ensure the fiberglass is pressed tightly against the foam.  The trick is, I would like to be able to create a re-usable vacuum bag.  Is this possible with epoxy?  I know this technique is used in wood working, with the reusable bag, but wood glue isn't epoxy.  I'd like to try to make this process pocket friendly.  Though- I'm not sure any kind of composite build is pocket friendly. 

I just want to get the thoughts of anyone out there who has experience with this.  Youtube can only take me so far. 
Title: Re: Vacuum Bagging
Post by: HunterWhite on December 11, 2020, 03:08:40 PM
The radio control glider guys did a lot of foam core wings that were vacuume bagged. It may be worth looking at that process. It was good for a lot of home brew designs. Cut the foam with hot wire or CNC machine, then bag.

Hunter
Title: Re: Vacuum Bagging
Post by: YEMX on December 11, 2020, 04:18:06 PM
I'm hoping it reall is as simple as vacuum bag material, seal tape, peel ply... 
Title: Re: Vacuum Bagging
Post by: Madd Hatter on December 11, 2020, 04:23:22 PM
As long as the resin doesn't contact the bagging material, you should be able to reuse it. The biggest problem I can see is getting the sealant to separate from the bagging film. It takes a real practiced hand to do that. As far as using peelply to act as a release of the breather and the part that just won't work. Peelply is great for giving you a bondable surface but isn't a release. I've always used TX1040 and TX 1080 teflon coated pooris armalon  http://5.imimg.com/data5/AM/LO/UR/SELLER-3517851/ptfe-coated-glass-fabric-250x250.jpg (http://5.imimg.com/data5/AM/LO/UR/SELLER-3517851/ptfe-coated-glass-fabric-250x250.jpg) as a release between the part and bleeder. You basically will need a pooris release, bleeder to allow the in traped air a pathway to the vac. Another problem you're going to find is getting the bag totally conformed to the part. Bagging a gun stock as opposed to bagging a R/C wing is 2 different things.
Title: Re: Vacuum Bagging
Post by: wolverine on December 11, 2020, 04:41:34 PM
yes it will work.  when i had my model shop, i made carbon fiber hoods for the local late model stock drivers using vacuum forming.  the thicker the material, the stronger the vacuum will be needed.  use a heavy plastic and spray it with a release agent before laying it on the epoxy soaked glass.  if done correctly, the vacuum will pull the epoxy into the glass while removing the air.  i had to experiment to find the right epoxy and cloth combination.  too much epoxy and you have a heavy item and it will develop too much heat while curing, burning off the release agent.  too little epoxy and the bond won't be strong enough.  use the least amount of epoxy as possible.  this will create the lightest and strongest item without heat causing cracks and warpage. 
Title: Re: Vacuum Bagging
Post by: YEMX on December 11, 2020, 04:45:01 PM
Oh for sure- a stock has so many more contours to contend with.  I wonder if I could just use spray release on the bagging material?  Hmmm.

Title: Re: Vacuum Bagging
Post by: YEMX on December 11, 2020, 05:43:06 PM
Also, at least for my stocks, I'm not trying to do a "true" wet lay-up.  My current process is:

paint a layer of epoxy over the stock, wait 2-3 hours until it's tacky, then over in fiberglass.  Let it completely set THEN do 3 or more layers of epoxy. 

For now, I'd only be using the vacuum bag for that initial stage.  So there will for sure be some epoxy bleed-through, but it's not as much as a "true" wet lay-up.  Thoughts?
Title: Re: Vacuum Bagging
Post by: Back_Roads on December 11, 2020, 05:49:00 PM
 That is what I was thinking release on the bag, some plastics do not bond to epoxy, one can test that before beginning a project. One thing that could be a hang up to the bag releasing would be a wrinkle that overlapped into the cured epoxy.
Title: Re: Vacuum Bagging
Post by: YEMX on December 11, 2020, 06:15:17 PM
Hmmm... So maybe peel ply, breather ply, with some release agent on the bag layer?  That should work, yeah?  I've got a vacuum pump on order  ;D ;D
Title: Re: Vacuum Bagging
Post by: Eddie_E on December 11, 2020, 07:11:24 PM
There are a few companies that make a bag seal that uses a solid rod and a C-shaped rod for a seal. I have used it many times on R/C airplane wings and it works well. Epoxy really doesn't bond to most plastics, but I have one or two that required me to start the peel with a knife, so I started wiping a little part all wax before bagging. I would guess a little lemon pledge on a paper towel would work just as well. I was doing inside out paint jobs, so Part All was my choice. Make sure you pull around 20 HG on a gun stock. The little mini pumps that run at 12 HG won't pull tight enough on the curves. This is where I bought the seals, bagging tubes, pump and bag fittings. https://store.acpcomposites.com/quick-lock-seals
Title: Re: Vacuum Bagging
Post by: YEMX on December 11, 2020, 08:18:10 PM
I really like that ACP Composites website- very nice lay out!  So here's what I'm thinking- since I'm not doing a traditional wet lay-up, I could layer up the stock like this:

non-porous release film, breather cloth, outer bag...  This way, the epoxy would still get pulled through the fiberglass, but I should be able to re-use the breather cloth and outer bag for a few stocks...  Again- all I need is to set the fiberglass into place, with no bubbles.  That's the goal.   
Title: Re: Vacuum Bagging
Post by: YEMX on December 12, 2020, 09:11:24 AM
I've been watching a few more videos- I guess my idea of using vacuum bagging on the first layer is called "de-bulking"...  It's used to get a perfect bubble-less first layer (usually using a mold) for subsequent layers to stick to.  Nice.  Also- someone mentioned this on my Elan re-hash build thread- cutting the fiberglass (or CF) so that the grain is 45* away (against?) from the surface you're working, will net better conformity to curves and such.  I also learned that my idea of laying fiberglass in the hard to reach areas (inside trigger well, inside of thumbhole) is what professionals do, and is also what de-bulking is!  I'm getting more excited about this vacuum bagging stuff every day!
Title: Re: Vacuum Bagging
Post by: Madd Hatter on December 12, 2020, 01:36:01 PM
I really like that ACP Composites website- very nice lay out!  So here's what I'm thinking- since I'm not doing a traditional wet lay-up, I could layer up the stock like this:

non-porous release film, breather cloth, outer bag...  This way, the epoxy would still get pulled through the fiberglass, but I should be able to re-use the breather cloth and outer bag for a few stocks...  Again- all I need is to set the fiberglass into place, with no bubbles.  That's the goal.   
Non porous release won't let the ply debulk (aka remove trapped air) the ply(s). 34 years working with aerospace composite layups. What release were you planing to use? I've used FEP for most of the years. You could perforate a non perf release to allow an air path. You also could just use a piece of blanket for a breather. I used to use N10 as a breather but we were also curing the part or laminate in an autoclave at temps between 250f and 400f using up to 125 psi. You are using room temp cure resin and just vac for your parts so you don't need anything fancy. It's too bad you live on the other side of the country.
Title: Re: Vacuum Bagging
Post by: YEMX on December 12, 2020, 01:54:46 PM
Non porous release won't let the ply debulk (aka remove trapped air) the ply(s). 34 years working with aerospace composite layups. What release were you planing to use? I've used FEP for most of the years. You could perforate a non perf release to allow an air path. You also could just use a piece of blanket for a breather. I used to use N10 as a breather but we were also curing the part or laminate in an autoclave at temps between 250f and 400f using up to 125 psi. You are using room temp cure resin and just vac for your parts so you don't need anything fancy. It's too bad you live on the other side of the country.

Oh- okay.  So I should use a porous peel ply, to make sure it debulks properly?  No idea on what release agent- I was thinking wax, or some release agent I have from Smooth On?
Title: Re: Vacuum Bagging
Post by: Eddie_E on December 12, 2020, 06:44:38 PM
I used to use 2 layers of paper towel before the breather cloth to absorb the excess epoxy without killing the breather cloth. I used some soft while upholstery padding from a fabric store for breather. It's used as the top layer over foam in upholstery before the cloth.
Title: Re: Vacuum Bagging
Post by: YEMX on December 15, 2020, 11:45:26 AM
Vacuum pump came in today!! 
Title: Re: Vacuum Bagging
Post by: YEMX on December 16, 2020, 05:37:00 PM
So supposedly this vacuum pump does 29" Hg.  Something that has been in the back of my mind, and also popped up in a discussion via PM- I wonder if this is TOO much vacuum for the foam I'm using?  I'll do a few tests to really find out, but now I'm really thinking about deformation due to too much vacuum...  Thoughts?
Title: Re: Vacuum Bagging
Post by: Blutroop on December 16, 2020, 06:01:54 PM
I can’t talk on how it’s done now but over 20 years ago I worked for a guy that was certified to repair sailplanes using Kevlar and carbon fiber.
He would make lightweight seats with vacuum bagging and burlap.. I kid not.

Anyways the part that might interest you was how simple his reusable setup was. A vacuum pump, two Pieces of plastic, and green sticky putty like teachers used to hang paper on walls as the seal between the two pieces of plastic.

I would experiment before I got too carried away with expensive release agents and all the nice comforts of industry support.

Also there are quite a few epoxy companies that would be able to educate you a bit on the phone in hopes of selling their products.

Start shopping and you’ll find there’s ultralight cloths out there, carbon kevlar composites, Tow, tape, biweave uni .. so many options once you find the right company catologs.

Never a big enough budget to try it all though!
Title: Re: Vacuum Bagging
Post by: Madd Hatter on December 16, 2020, 09:11:28 PM
Get your self some of those vacuum bag storage bags 😜 You should be able to get a good seal with one as long as you can get it confirmed to the stock.
Title: Re: Vacuum Bagging
Post by: Eddie_E on December 17, 2020, 06:05:12 PM
My un-scientific opinion on foam is that  the lowest grade of white EPS foam distorts at 13 HG. Pink Foamular 250 and the slightly stronger Dow blue sold in super hardware stores start to deform at 23 and 24 HG. Dow hi-load 40 takes full vacuum with a little care at the edges. Hi-load 60 and Plaza Mate easily take full vacuum, even with sharp edges.
Title: Re: Vacuum Bagging
Post by: Nvreloader on December 17, 2020, 08:24:29 PM
Tom
What about a Food Saver Vacuum machine, you can make the bags as long as you want,
and there 2-3 different widths etc....... ;)

I had a friend that used to use one of these machines and dyed his thin laminates for gun stock coloring.

HTH's
Don
Title: Re: Vacuum Bagging
Post by: YEMX on December 17, 2020, 10:35:33 PM
Tom
What about a Food Saver Vacuum machine, you can make the bags as long as you want,
and there 2-3 different widths etc....... ;)

I had a friend that used to use one of these machines and dyed his thin laminates for gun stock coloring.

HTH's
Don

It's worth looking into for sure- though, I don't think they're flexible enough for my purpose.  At least not for gun stocks...

My un-scientific opinion on foam is that  the lowest grade of white EPS foam distorts at 13 HG. Pink Foamular 250 and the slightly stronger Dow blue sold in super hardware stores start to deform at 23 and 24 HG. Dow hi-load 40 takes full vacuum with a little care at the edges. Hi-load 60 and Plaza Mate easily take full vacuum, even with sharp edges.

After doing a google search, I'm not sure there's a local source for the Dupont highload foams...  I'll keep checking though.  I wouldn't ever use regular styrofoam.  The lowest grade foam I'd ever even consider using is the pink or blue XPS foams.

If I can't get a denser foam locally, I may have to buy pourable urethane expanding foam to make my own blanks...  Full vacuum is 14 psi compressive pressure?  So all I'd have to do is find something that's well above 14 psi...  Right?  Or is there more to it? 

This idea is getting more complicated by the day!  ;D
Title: Re: Vacuum Bagging
Post by: Spektr02 on February 14, 2021, 01:09:46 AM
Sorry Im late to the discussion.  As a Tool Engineer at Boeing, we used silicone Vac Bags for reusability. 
Title: Re: Vacuum Bagging
Post by: YEMX on February 14, 2021, 04:36:41 AM
Sorry Im late to the discussion.  As a Tool Engineer at Boeing, we used silicone Vac Bags for reusability.

Now there's a thought!  I hadn't come across silicone vac bags in my research.  I'll have to take another gander on the web!
Title: Re: Vacuum Bagging
Post by: Madd Hatter on February 14, 2021, 11:28:52 AM
Silicone bagging wouldn't work for what you are doing IMHO. Silicone bag is for reusability for the same part and also for use in a autoclave which uses heat and pressure. At least that's what we did for the Nasa stitched wing program.
Title: Re: Vacuum Bagging
Post by: YEMX on February 14, 2021, 11:38:45 AM
Is the silicone bag molded into the general shape of the piece that's being vacuum bagged?  Or is it a thin flexible skin, similar to the disposable bagging materials?  I just figured that a thin silicone membrane would be cheaper in the long run, since I'm not throwing it out after every use... 
Title: Re: Vacuum Bagging
Post by: luge007 on December 19, 2021, 05:52:55 PM
SO, where (10 months later) did this project end up??  Inquiring minds want to know. ;)



Title: Re: Vacuum Bagging
Post by: YEMX on December 20, 2021, 01:44:50 AM
SO, where (10 months later) did this project end up??  Inquiring minds want to know. ;)

I've got the vacuum pump, but I haven't figured out what foam I want to use, or if I should cast my own blocks, or really how to proceed with the foam core.  I know I want something far more dense than the pink (or blue) insulation foam.  Also, I haven't decided on what kind of fiberglass to use either.  I'm not sure I want to step up to CF, as it's really expensive.  I'm also not sure if I want to do a wet lay up then vacuum bag it, or do a resin infusion...  I have no experience in either.  I haven't given up on the idea, I just don't know how to proceed.  Also, I've got a new compressor, and I've FINALY got a tethering reg for my Great White tank, so I can FINALLY do looooong tuning strings.  Plus, silly adulting has gotten in the way too.  LOL 

Basically, I put the cart before the horse, and I don't want to waste a lot of money for an experiment!  LOL  But I WILL get back to this idea someday!
Title: Re: Vacuum Bagging
Post by: HunterWhite on December 22, 2021, 02:56:12 PM
The guys that made RC airplanes used blue foam, or pink foam from Lowes or Home depot for cheap experiments. The favorite for high-tech was Dupont Styrofoam™ Brand Highload 40 or 60  Extruded Polystyrene about 20 years ago, now they also have 100 psi foam on their website.

Hunter
Title: Re: Vacuum Bagging
Post by: Firewalker on December 22, 2021, 04:51:52 PM
I'm one of those glider guys, we made pink and blue cores with either carbon fiber or glass,  depending on your specs. The Goldberg Gentle Lady style (1 meter) sail plane (powered) was our big seller.

I used 6mil roll plastic and spring clips for bags and it went in the trash after peeled it off. Flash was trimmed off and sanded smooth ready for next coat.

Volcanic rocks were used for excess epoxy take up (messy but they do work, just throw a layer of paper towel over them or they will poke through the plastic) and an inline pot was used for a safety for the pump.

Ice maker line for pull down was sacrificial and cheap!

Wing sets are easy, I bet a stock would be a bit harder.
Title: Re: Vacuum Bagging
Post by: MJP on January 04, 2022, 04:58:06 AM
For the foam, any will do. Just what you can get cheap. The foam it self wont do much, its just support for the fiber. After hardening you can melt the foam away with thinner and the part is just about as rigid as with it.

I use tubular 600mm VACtite vacuum bags for long projects and sheet for bigger. Usually you'll get three to four uses from one bag, after that there starting to be too many holes in it no matter how gently you handle it.

I wet the fibers on top of piece of bagging material then put another piece of baging on it.
Use a rubber squeezy to get all the air and excess resin from the laminate and put it in the mold. Lay everything you need and peel ply on top, the perforated releasing film on it,  then you breather material that will capture any excess resin. Seal the bad and pull vacuume. Dont go much below 300-350mBar or you'll risk collapsing the foam core. I tested around 100mBar and you'll get too dry laminate.
Hope this helps

Marko
Title: Re: Vacuum Bagging
Post by: MJP on January 04, 2022, 04:59:50 AM
Oh yeah, the fiber and epoxy amount must be weighed so you dont mess up the bag.
And be sure your breather material can absorb the excess.
If using the squeezy method you'll most likely be fine and dont have too much resin.

Marko