Vacuum bagging - cheap setups

[erikgreen]

Hey all -

I figured we're in a lull in some of the bigger resto type threads, so I wanted to see if anyone had any experience doing vacuum bagging with cheap materials.

For those not knowing, vacuum bagging is the process of using an airtight membrane with a few layers of porous materials under it all applied over a still wet fiberglass layup. A vacuum pump sucks the air out, with the result that 10+ PSI is applied all over the bag as a giant flexible clamp. This lets the glass cure with an optimal ratio of resin to glass for strength and weight, forces the glass to follow molds/wood/whatever tightly without too many problems with radius edges, sucks out bubbles, and generally makes a better quality laminate than hand lay up. Excess resin is pumped out with the air.

The drawback is, of course, cost and complexity. You need at least:
* A vacuum pump
* some tubing
* A pressure tight vessel to collect extra resin
* A couple valves
* a fitting to attach the tubing to the bag
* bag material
* a flow layer, something that won't crush flat but will allow resin to flow through it
* Sealing tape

Note that you can instead pressure mold items if they're flat: Eg. you can take a bulkhead after you cut it out, put out a plastic base on a flat surface, then stack glass and resin, the wood, more glass and resin, a plastic cap sheet, and a flat board larger than the item as a clamping face. Then you put weight or a bench press on it, and get some of the advantages of bagging. But it only works for flat items, and only items small enough to fit on your table, and clamping pressure needs to be even. Bagging can be used on a whole curved hull at once if desired, making your whole hull layup wet on wet, a single piece of glass.

So, I'm posting the question here: Does anyone have examples of vacuum bagging they can share? I'm looking for something along the lines of "I use this refrigerator compressor, 3 mil poly plastic, some plumbing fittings, and paper towels, and it works ok" or "I buy real bagging supplies from XXX, they're cheap and work well".

I'm looking to selectively bag parts of my next project for ease of clamping and to get a nice, solid, light layup.

Thanks for any info anyone can share,

Erik

 

[oops!]

Re: Vacuum bagging - cheap setups

i havent done any vac bagging yet......but i was discussing it in great detail with a few local pros......they told me a 5 mil poly......and plasticine as the bag seal......roll it out in a rope......and press the plastic into it.....we didnt discuss pumps.......or line drain......but its got to be disposable....as the resin is catylised

 

[oops!]

Re: Vacuum bagging - cheap setups

btw.....from the posts in the hull thread.....capt jason....(now "just jason") mentioned he had done some or was possibly suggesting to have done some.

 

[Bondo]

Re: Vacuum bagging - cheap setups

* A vacuum pump
* some tubing
* A pressure tight vessel to collect extra resin
* A couple valves
* a fitting to attach the tubing to the bag
* bag material
* a flow layer, something that won't crush flat but will allow resin to flow through it
* Sealing tape

Ayuh,...

So far,.... All I see is,...
* A ShopVac,..
* A roll of the thicknes Plastic you want,..
* A roll or 2 of Ductape,..
* A couple pvc valves,..

The Flow Layer is the fabic used in the composite isn't it,..??

I question whether the added Effort would be worth whatever added values created by it,..??

I Can see a major benefit if glassing Vertical surfaces,....

 

[erikgreen]

Re: Vacuum bagging - cheap setups

Ayuh,...

So far,.... All I see is,...
* A ShopVac,..
* A roll of the thicknes Plastic you want,..
* A roll or 2 of Ductape,..
* A couple pvc valves,..

The Flow Layer is the fabic used in the composite isn't it,..??

I question whether the added Effort would be worth whatever added values created by it,..??

I Can see a major benefit if glassing Vertical surfaces,....

Or Eg. round ones, or any edge that would otherwise form bubbles.

The problem with the shop vac is that whatever you use needs to hold the vacuum until your resin sets, preferably until it fully adheres, which can be hours... most shop vacs won't take that.

PVC fittings might work, provided you have one that's meant to go from a hose to a flat tank wall or fabric tank. I figure I could just buy a real fitting for this part. PVC valves would work otherwise I think.

Plastic probably can be the generic stuff from Menards.

I may have the terminology off for "flow layer".. my understanding is that on top of the glass and resin you have a porous layer of fabric for "peel ply" that gives you the finish on the glass you want but allows resin to flow through it or away, and is a material that won't stick to epoxy, like nylon or similar. Then a layer of non crushable yet porous material that lets the excess resin flow linearly to the drain for the whole setup. Then the air bag. You actually lay the whole thing up dry and seal it, then you can flow the resin in via inlet tubes once you pull a vacuum.

Maybe someone else can chime in on how vac bagged materials compare to non vac bagged/hand layup? Anyone seen KnottyBuoyz lately?

Erik

 

[jonesg]

Re: Vacuum bagging - cheap setups

I consider it to be more attractive for aviation or world class CF racing hulls, (yachts kayaks racers), otherwise...I never have a problem with molding.
The way I see resin slopped onto boats I don't see weight as a critical issue, there are techniques that can reduce weight without vac bagging.

There are small elec vac pumps that sell for less than $75, or there used to be. Check out the videos on youtube.
http://www.youtube.com/results?search_query=vacuum+bagging&search_type=&aq=f

 

[ondarvr]

Re: Vacuum bagging - cheap setups

Bagging isn't difficult and works well for bonding cores in place and was somewhat popular for a while, but if you're going through the hassle of bagging, you might as well go all the way and infuse the part.

It can be done with low cost supplies, but like anything else, works better with the right stuff. Poly sheeting tends to leak, so a higher CFM vacuum pump will work better, you can use duct tape (it leaks) or butyl tape and polyethylene tubing. If you use a breather fabric to remove excess resin it needs to be removed before the resin has hardened completely or you?ll need to grind it off the laminate. A one off job will run a couple hundred bucks in supplies for the bagging process, some of it can be reused, but much of it will be trashed after each use, so the cost is much higher than hand laminating. H/F has a cheap vacuum pump for about $69.00, but I?ve never seen one, and the specs listed don?t say much about it. I?ve used the pump from a refrigerator before, but the volume is low, so any leak will create problems, with no leaks even a low CFM pump works fine.

Lower viscosity resins with longer gel times are commonly used. Typical laminating resins can be used, but lower viscosities work better, they allow the resin to flow to where it?s needed, or out of the laminate altogether. For those with less experience longer gel time resins work better because it will take time to wet out all the glass, get the bag in place, then pull a vacuum on it.

All the supplies need to be upgraded for infusion so the cost goes up.

If you have experience in working with fiberglass and want a new challenge or a way to bed cores like sheets of balsa or foam it works well. For one off smaller stuff it?s normally more work and the results aren?t enough better than hand lamination to bother with.

 

[erikgreen]

Re: Vacuum bagging - cheap setups

Okay, cool, thanks for the info.

I'm thinking I'd like to use it to bond glass with poly resin around a round foam core (think buoy) and for making nice clean laminations on some plywood bulkheads. I was also thinking the vacuum bag could be used for a transom lamination... it'd be a nice even pressure across the two sheets of ply.

But maybe I should just build a basic pressure setup for that... a shop press with a ply table and a couple of bits of reinforcing steel would squeeze out excess resin pretty well.

Erik

 

[ondarvr]

Re: Vacuum bagging - cheap setups

For bedding plywood and other cores it works well, like you said, it gives a nice even pressure across the entire surface. One issue with uneven surfaces or shapes with multiple contours is getting the bag to lay down and not bridge over any low spots or in the radius, it can be done but for complicated shapes takes time and experience. Any area where bridging occurs will fill with resin and with no glass it will tend to crack. When clamping a layup like when placing plywood in the transom you don?t need much pressure, just enough to seat the wood, if too much pressure is applied the resin is squeezed out and the bond will be poor.

 

[metriccrescentwrench]

Re: Vacuum bagging - cheap setups

OK, I've done a bunch of vacuum bagging when I was building an airplane from plans. Yes, it can be done cheaply if you're a good scrounger. In my opinion though, I've got to question how much bagging bought me in terms of better/lighter parts over just being careful to do a good layup without excess resin in the first place. But hey, don't let me discourage you, go ahead and try baggin some parts and see what you think.

For my vacuum pump I found a used HVAC vacuum pump for cheap. You don't want to bag at anywhere near full vacuum from that thing, lest you squeeze every drop of resin out of your part. You can use a small needle valve to bleed air into the vacuum line, and monitor the vacuum with a guage. Somewhere in the range of 5 inches Hg worked good.

I've heard of people using refridgerator compressors, and see no reason why it wouldn't work, but I haven't done it and can't offer any information on that.

Run a piece of nylaflow tubing from the vacuum pump up to the work area as your vacuum line.

I'll describe the setup I used for bagging flat parts, or at least parts that were flat on one side. That's the easiest. I used either a large piece of painted steel or a 4' x 8' piece of coated bathroom siding (from Home Depot) as my base. If you're just glassing one side of your part, lay the wood/foam part on the base with wax paper under it. Later on, if you want to glass both sides of a part at once it's very possible, but I'd start with doing one side at a time (or some practice parts) to get the hang of it.

Glass the part, then put "peel ply" on the glassed part. (Peel ply can be any fabric that will release cleanly from a fully cured part. Polyester or nylon fabric from your local fabric store usually works, but test it first.) Peel ply will give tha part a uniform surface which is nearly ready for paint or for bonding to other parts. After peel ply put on a layer of release film, which is usually a thin perforated plastic which allows resin to pass through. It's available at www.wicksaircraft.com. Then comes the bleeder ply, which can be anything that will absorb excess resin. This can be from the fabric store, get the thick fluffy material used for making comfortors, etc. In a pinch I've used old towels and blankets.

To allow for a path for the vacuum to "flow" lay down some extra bleeder material from the part going off to one side where you'll put your vacuum line. Run the vacuum line right into this material. For sealing I found that cheap caulk worked well, lay down a bead around the part, and both over and under the vacuum line. And finally, 5 mill plastic sheeting works well as the "bag", cut it oversized and lay it down over the part, pressing it into the bead of caulk.

When you turn on the vacuum there may be a few leaks, manipulate the plastic sheeting/caulk interface to seal them. Monitor the vacuum guage until it stabilizes, and let the part cure. It's easier to remove the part if you can do it before it's fully cured, but it's not the end of the world if you can't stay around and end up working with a fully cured part. Oh, the pump will of course need to stay on until the part is cured (at at least nearly cured). If you remove vacuum too early the glass will expand to it's previous thickness and will be resin starved.

There, that's my vacuum bagging on the cheap 101 discussion. I hope I explained everything ok, just ask if there are any questions.