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Old May 04, 2001, 05:12 PM
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Albuquerque, NM
Joined Feb 2000
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Vacuum bagging on the cheap?

I was considering trying to vacuum bag some wings in the near future, and thought about different ways to do it (cheaper than a 300 dollar vacuum system).

Would any of the aquarium air pumps sold at pet stores be sufficient to provide the vacuum needed? I assume you could just put the input (suck) in the bag, and let the other end blow. Any thoughts?

Greg
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Old May 04, 2001, 05:24 PM
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MikeC's Avatar
Albuq, NMex USA
Joined Jan 2001
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Hey Greg,

Put a sign up at Hobbies N Stuff and maybe you could get one used. There may be a soaring club member with one for sale.

Mike
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Old May 04, 2001, 05:29 PM
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Stavanger, Norway
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I have seen reference of a small aircompressor intended for use with airbrush placed inside the bag in some sort of woodbox around it and let the hose go out - havent tried it yet but seem viable. I have a $70 aircompressor that I just might try that with.

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Old May 04, 2001, 05:32 PM
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Winchester; Ohio
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You can use one of those but they will only pull 6" or 7" of vacuum. If you can scrounge up a used compressor from an air conditioner or refrigerator they will work great. Ive also heard of guys using a Mighty Vac hand pump; and if your bag is sealed real well you can get great results with one.
I purchased a vacuum pump off of ebay (Shop around) and my supplys from CST.
Also Aerospace Composite has a nice kit with a pump similar to an aquarium pump for $120.00 http://www.acp-composites.com/acp-vbs.htm
The $300.00 kits you mention include a pretty heavy duty pump that you can find better options for.
Adam
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Old May 04, 2001, 07:07 PM
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Stavanger, Norway
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How much suction is sufficient for a "good" vacuum setup? I just tested my compressor in a sealed plastic bag and it dented the corners of the foam blank (white) placed inside.

If viable then I envision the compressor inside a wooden box with a 1/2" hose running from the bag feeding the box where the positive pressure line exist into open air. This way placing the compressor inside the bag is avoided.

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Old May 04, 2001, 09:09 PM
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Carver, MA USA
Joined Jun 2000
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I don't think air compressors are designed to run in enclosed spaces. They usually depend on surrounding air for cooling the pump and motor. It might present a fire hazard. Normal bag time is 24 hours in warm weather or under a heat pad. That's a long time to seal up the compressor. Compressors also are set to establish a tank pressure and are not set to regulate a vacuum. Hunt around for industrial surplus suppliers. Very often they can supply a used commercial duty pump for $50 or so. Another $25 will get you a vacuum regulation switch from Aerospace Composites. Make a reservoir tank from anything from 6" PVC with end caps to an old propane tank. The tool can do more than just skin wings.
I pull delicate stuff to 10" of mercury. Plywood or Obeechi on blue foam has no problems with 15". Clamping and laminating of wooden parts can go over 18" with no harm.
Ron
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Old May 04, 2001, 09:44 PM
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Lambertville,nj, usa
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I've been using a $15 aquarium pump for several years with good results. When you remove the cover, the intake hole on the side of the diaphram pump is easy to spot. Just Zap a piece of clear plastic hose to the hole and you have a vacuum pump. For bags I use 2-4mil plastic drop cloth cut to the appropriate size. For breather cloth I use Bounty brand paper towels doubled over(they are thick and work as well as felt). To seal the edges of the bag I use the cheapest caulk I can find, usually $1 or less. Everything is disposable except for the pump and hose. Total investment @$30. Give it a try.

Ed

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Old May 05, 2001, 05:15 AM
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Ed B has a good thing going on. I don't know much about the aquarium pump vacume #s, but the rest is good stuff. In garage projects I try to use the cheapest supplies possible, so much material is wasted when vacume bagging (I use to do it for a living). A couple words of caution. Not all plastic drop cloths are good bagging material. Some stuff leaks really bad. It'll have very tiny pores in it and you'll never get your bag to suck down well. The best stuff I've used is ACE Hardware brand drop cloth. Also, cheapy white foam isn't the best bagging foam. Over time it'll crush under vacume very easily. There are probably people who have done it under low vacume (like 5-10") but I've never really messed with it, don't like the idea of squished airfoils. Blue foam is ideal but it is pricier. My home vacume pump is a low end dual diaphragm industrial vacume pump (around $60-$70) and will pull up to 15-17". I got vacume line and "T" line splitters from the auto parts store (aquarium tubing crushes past 15"). You definately want a one way valve in your main line. Otherwise you won't get optimum vacume. Also, if you are going to use an air bleeder (paper towels etc) in a fuselage or an application without mylar, make a perferated layer out of the drop cloth plastic (use a thick needle, scratch awl, pair of sharp dividers, etc and punch lots of holes into the plastic). This will give you a non stick layer that will allow air and excess resin to pass through to the paper towel bleeder and you won't end up with paper towels stuck to your glass work.
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Old May 05, 2001, 08:33 PM
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Butler, Pennsylvania, United States
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An inexpensive (sometimes free) vacuum pump is a compressor off of a refrigerator or a freezer. I've heard that they work well, they certainly can be cheat if you look around. Just one thing, you need to put a long vertical tube on the exhaust to keep the oil from flying out of the thing.

I bought a used gast rotory vane pump and used it quite a bit this past winter. I only paid $75 for a used gast. To be honest, the gauge, vacuum switch, check valves cost more than the pump.
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Old May 05, 2001, 09:40 PM
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sloflyer: when I bag a set of wings, I do it as though I was going to use heavy weights piled on top of the cores,ie. keep the cores in their beds. If you want to try it without the beds, a layer of mylar with mold release on it would be appropriate.

Ed
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Old May 05, 2001, 10:11 PM
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Kansas, USA
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I have tried the aquarium pump. They pull 4" to 5".
Mike
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Old May 06, 2001, 12:58 AM
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So ED B, you don't need anything to prevent the bounty paper towels from adhering to the resin?
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Old May 06, 2001, 02:14 AM
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sloflyer, does this answer your question.
Quote:
Originally posted by Troy:
Also, if you are going to use an air bleeder (paper towels etc) in a fuselage or an application without mylar, make a perferated layer out of the drop cloth plastic (use a thick needle, scratch awl, pair of sharp dividers, etc and punch lots of holes into the plastic). This will give you a non stick layer that will allow air and excess resin to pass through to the paper towel bleeder and you won't end up with paper towels stuck to your glass work.
There's actually professional stuff I use to use at work for this but it's almost as much as carbon per yard. The plastic works just as well (less precise hole count of course )

Anybody out there bagging glass over cheapy white expanded bead foam? Curious what the results were and at what pressure.


[This message has been edited by Troy (edited 05-06-2001).]
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Old May 06, 2001, 02:21 PM
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Thanks ED B and Troy, I've heard of the material that was perforated, just didn't know where to find it, or an acceptable substitute.
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Old May 07, 2001, 12:48 AM
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Takapuna, Auckland, New Zealand
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Troy--I've made 9 Sport400 wings out of ordinary white foam so far this year!!
This wing is a thin RG14 section and the tips are modified to 6% thick with camber of 1.
The finish isn't like on blue foam--but fast-light and if you have the gear --a lot cheaper than a 1/32 skinned balsa wing.
No filler into any of the 9--but I did a super thin MH43 based s400 pylon wing this weekend with model magic spread over (very wet) then sanded off. Bagged unpainted in mylar --nice.
Incidentally these cores/ baggings include the leading edge. Ailerons are cut leaving the top skin as a live hinge--magic tape over for insurance.
Pressure has been 10 inches of Hg or less. Just looked up the conversion and that is only 5 pound per sq inch. Not sure now if that is why it worked or if I could pile on more pressure
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