vacuum bagging set up recomendation

Discussion in 'Composites' started by jany77, Dec 6, 2019.

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  1. Dec 6, 2019 #1

    jany77

    jany77

    jany77

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    Hi , can anyone please recommend decent vacuum pump set up ,I would prefer one run on electricity instead of air ,also on budget like most of us .Thank you
     
  2. Dec 6, 2019 #2

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    How big are the parts you want to do and what processes are you using? Infusion? Wet layup and bag? Whole wing skins or fuselage halves?
     
  3. Dec 6, 2019 #3

    BoKu

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    If you're just starting out, I'd suggest getting a $50 HVAC evacuation pump off of eBay. That will get you started with small projects, and you can use it as a backup or extra pump when you move on to larger projects. Right now we're using a 1/2hp 2-stage HVAC evac pump as our main pump, and we've drawn down and held bags up to 100 ft^2 in area with it. It's not the greatest CFM, so we use an old water heater as a vacuum reservoir, and we sometimes use a shop vac to do a pre-draw that gets all the extra air out of a loose bag.
     
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  4. Dec 6, 2019 #4

    Aviacs

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    Since integrity of the bag & seal are essential, you won't actually need a very big pump, paying attention to the basics.
    My dad gave me a Cenco Megavac from his lab back in the 80's, & I've used it ever since. The last few .1 Torr (of a Cenco type pump) are irrelevant for practical pressing, so less deep vac pumps work fine. The nice thing about the Cenco, though, is once it pulls the vacuum, it will run all night with minimal current draw. The bad part of a cenco is that they are oil immersed pumps, and there will be a fog of oil vapor around it after a few hours run time.

    Got a 5HP vane pump out of my next door neighbors milk parlor when they were flooded out & scrapped it in the 90's. I've never needed that capacity to hook it up. But smaller vane pumps would work fine.

    If you are buying new, get something with 1/2HP or larger. If the source is free or low cost, small to even decent sized parts can be pressed with 1/4HP.

    Despite being rigorous about sealing, even the tiniest leak or membrane porosity adds up over very short time, so I let the pump run until the part is cured. A reservoir is a good alternative, but i prefer portable, vac-bagging jobs aren't routine, and space for a reservoir (tank) is at a premium here. If vac-bagging will be done somewhat routinely, it could be worth plumbing a system with a good sized reservoir.

    Depending what you are making, sometimes pressure bagging is more convenient or appropriate. I use collapsible discharge hose.
     
  5. Dec 6, 2019 #5

    Gary Grommon

    Gary Grommon

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    good place to go is here:
    https://www.joewoodworker.com/

    he has got some pretty decent vacuum stuff.

    like this:
    https://www.veneersupplies.com/products/Vacuum-Pump---Thomas-315-CFM-120-VAC.html

    or how to build a pretty good system:
    https://www.veneersupplies.com/products/Project-EVS-Auto-Cycling-Pump-Vacuum-Press-Kit.html

    also at oshkosh the CozyGirrrl:
    http://www.cozygirrrl.com/

    did light bagging that got the fiberglass to lay down better with out a big set up. they used like a fish tank aerator for a pump I think and saran wrap and plastic tubing. It looked pretty easy and would have save me some effort for small parts. I was skeptical at first but it worked really well.
     
    Last edited: Dec 6, 2019
  6. Dec 6, 2019 #6

    Jay Kempf

    Jay Kempf

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    Here's the pump I am using now:

    It's a bit of a beast for the stuff I am doing but I believe in working a bigger unit less hard than overdriving a lesser unit. I have it hooked up to a vacuum switch so it can cycle against any leaks and I can dial any pressure I like. I have always hooked up my vac pumps that way. First one I built was 25 years ago and was just a surplus fragged out refrigerator compressor. I just used the low pressure side input. Used old freon and/or propane grill bottles as makeshift reservoirs. Choke pull off with a microswitch and opposing spring works great as a regulator.

    https://www.ebay.com/itm/5-Gallon-V...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
     
  7. Dec 9, 2019 #7

    jany77

    jany77

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    Thank you guys for answers ,my parts are mostly flat with no more than 6 square feet of area .
     
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  8. Jan 1, 2020 #8

    lr27

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    For 6 square feet, you don't need a very large pump. Someone mentioned aquarium pumps, but they're not very strong. If you're bagging over bead foam, that's ok, because any more vacuum would squash it. Maybe an old refrigerator compressor? I've never tried one, but lots of people report that it works. I use a Gast vacuum pump, but there are probably cheaper choices. If you're going for a vacuum switch, a small vacuum reservoir as suggested by Jay Kempf will lengthen the cycle. Don't go too big and flimsy on your vacuum reservoir, though I suppose big and sturdy is ok. A 55 gallon drum would be an example of too big and flimsy, and I've seen the results. One of these days, I'm going to dig up an old, spherical oceanographic buoy I have and use that. It's a good idea to insert something, like an automotive fuel filter, on the intake side to catch anything that might otherwise get sucked into the pump. You can put another one on the exhaust side as a muffler. Another simple muffler is to glue two brass tubes into the neck of a bottle. Put the exhaust hose on one. Makes a difference. Maybe a big pump needs a bigger bottle.

    A quieter pump, a longer hose, and/or less ambient noise make it easier to hear leaks. A more powerful pump makes the leaks louder. If your high frequency hearing is shot, there are devices to convert sound to lower pitch. One such device is a so-called bat detector. As I recall, you can find simple circuits for bat detectors on the web. One of these days, I'll have to try it, because finding leaks is often difficult for me.

    A vacuum gauge is handy, especially if you're trying to figure out if you've eliminated all the big leaks. You can also use it to evaluate your vacuum settings. Sometimes, if I'm bagging something and I don't want to squash it, I'll bleed a little air in with a needle valve or something, the kind that you get from aquarium stores. But that's because I'm too lazy to set up a vacuum switch, which would save wear and tear on the pump. I suppose a needle valve makes for steadier pressure.

    For vacuum hose, I use thick walled latex tubing, aka an old RC glider high start that doesn't perform very well any more. However, that's just because I have it around. I use auto body strip caulk to seal the bags, and it works about as well as the official bag tape. More Tite works but is more annoying to work with. It may take longer to get the leaks out. I use paper towels to let air move through the bag toward the hose.

    I only vacuum bag occasionally, and I haven't done much with composite layups except for a week working with a boat builder many years ago. My last significant vacuum bag project was an amazingly strong work bench top. I cut a sheet of 1/2 inch plywood in half and glued it to either side of a piece of 2 inch thick extruded Styrofoam. I think you could probably drive across it with a truck, but it's light enough to pick up. I used Gorilla Glue, which was probably a mistake because I could have used more working time to find more leaks.
     
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  9. Jan 1, 2020 #9

    Aviacs

    Aviacs

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    Describe the actual dimensions?
    Like long and thin? or square?
    Materials? (wood or composite)
    If wood, what kind of glue?

    Will you use an actual bag, or tape membrane to an oversize backer/form?
     
  10. Jan 5, 2020 #10

    lr27

    lr27

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    If you're pulling out excess air with a shop vac to start, you can get it to pull a little harder when it starts to bog down by bleeding in a little extra air. I discovered this when I had to use a shop vac to pump out my flooded basement. Ugh! Everyone else had the same problem and had bought up all the real pumps.
     
  11. Jan 7, 2020 #11

    opcod

    opcod

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    If you plan on proper part and with high strenght for the work you put and money, you will not go with any shop vac stuff. Bare minimum is a 1/3 motor on the vacuum pump. Oil based work only with tight bag with no hole. But that is easy, as you can take your time to make a perfect seal.
     
  12. Jan 7, 2020 #12

    TMann

    TMann

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    Try this previous post which has a schematic: Here
     
  13. Jan 14, 2020 at 5:44 AM #13

    lr27

    lr27

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    OTOH, while you're waiting for the super duper, but slow pump to pull the bag down enough to hear the leaks, I've already pulled the bag down with a shop vac, switched to my own super duper pump, have found the leaks, and plugged them. Plus, in some few applications, the shop vac pulls enough by itself.
     

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