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Re: vacuum bag [Re: pgp] #249200
06/05/12 06:00 AM
06/05/12 06:00 AM
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Richmond, Va
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soccerguy83 Offline
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David gets the prize on this one, I didn't even think about that, but he is absolutly right.


Brian C.
H14
H16
-- Have You Seen This? --
Re: vacuum bag [Re: ksurfer2] #249218
06/05/12 08:44 AM
06/05/12 08:44 AM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
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Originally Posted by ksurfer2
OK smarty pants......why do beer cans explode after you shake them? What is it about Mentos that makes coke bottles blow up? Those of us on the wrong side of the bell curve need real world knowledge! crazy


1) They don't. Until they are opened. Fluid dynamics and answer #2
2) Nucleation sites


Jay

Re: vacuum bag [Re: soccerguy83] #249219
06/05/12 08:46 AM
06/05/12 08:46 AM
Joined: Dec 2001
Posts: 5,590
Naples, FL
waterbug_wpb Offline
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Originally Posted by soccerguy83
David gets the prize on this one, I didn't even think about that, but he is absolutly right.


Unless the interface area is protected by a non-volatile solid/liquid


Jay

Re: vacuum bag [Re: waterbug_wpb] #249221
06/05/12 08:56 AM
06/05/12 08:56 AM
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mini Offline
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Pete,

Must you complicate everything? wink
The whole point is to apply "pressure" so you consolodate the laminate and remove excess resin. Vacuum is a conveinient way to get about 14lb/in. You can get 80-90 out of cheep home compressor if you can manage to build a vessel to hold it. A pressure chamber is a lot more complicated than tacky tape and plastic film, but it is possible to achieve the same net effect.
Rollers and sqeegees work to some extent with open molding, but if there any loft to your fiber pack it is extremely difficult to get a good fiber to resin ratio.

Re: vacuum bag [Re: pgp] #249223
06/05/12 09:08 AM
06/05/12 09:08 AM
Joined: Jun 2001
Posts: 778
Houston
carlbohannon Offline
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Yes, but you just end up with a really crappy 1 stroke piston pump

Look at a Manometer. Fill a tube taller than 33 ft with water. Upend the tube of water into a container of water. The column of water will drop until it is supported by the air pressure (~33 ft). The pressure in the void in the top of the tube will be the vapor pressure of water (~0.5 psi). If you use an IV bag and a flexible tube, start with the tube full of water, the open end in the container of water and then just hoist the bag up a tree.

Lets assume you are going to use this thing to pull a vacuum. Assume 1 ft of that tube has the same volume as what you are trying to pull a vacuum on. If you make your tube 43 ft high the best vacuum you can pull will be 14.7/11 +0.5(Vapor pressure of water). There are loses and other factors but I don't remember what they are.

I actually saw someone try this once as a college project. They were able to pull a couple of psi of vacuum. They then showed a hand powered lab vacuum pump beat the hell out it.

A better system is a vacuum oil changer. I have a metal one leftover from my big boat days but it works like this

http://www.liquivac.com/buyonline

I can get about a negative 7-8 psi per the gauge, if I work really hard and when I finish with, I can change the oil in my lawnmower

Re: vacuum bag [Re: mini] #249224
06/05/12 09:16 AM
06/05/12 09:16 AM
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South Carolina
Jake Offline
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the nice thing about the vacuum, though, is that it tends to expand, burst, and evacuate bubbles in the resin of the layup. Applying just external pressure would compress those bubbles and they would remain in place.


Jake Kohl
Re: vacuum bag [Re: Jake] #249226
06/05/12 09:56 AM
06/05/12 09:56 AM
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mini Offline
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Originally Posted by Jake
the nice thing about the vacuum, though, is that it tends to expand, burst, and evacuate bubbles in the resin of the layup. Applying just external pressure would compress those bubbles and they would remain in place.


True, but the nice thing about large differentials in pressure (this includes the difference between atmospheric pressure and the applied vacuum, or atmospheric and the applied pressure) is that as long as the material is flowing, the air will rush to the flow front. In production comression molding uses this to get void free laminates. Puddle the resin in the center and as you apply pressure the resin flows out and takes the air with it. Air voids (short circuits)under vacuum will not "move" either without flow.

Re: vacuum bag [Re: pgp] #249229
06/05/12 10:17 AM
06/05/12 10:17 AM
Joined: Jan 2009
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pgp Offline OP
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So which is the superior method for home building dagger boards, rudders and other relatively "flat" panels, vacuum or pressure?

For pressure I'm assuming you could put the part between two flat plates and pile weight on it. No? Yes?

Inquiring minds...

And I got this in the "mail" this morning. Anyone know anything about it? http://www.jamestowndistributors.com/userportal/main.do?&campaign=email060512

Last edited by pgp; 06/05/12 10:21 AM.

Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: vacuum bag [Re: pgp] #249231
06/05/12 10:30 AM
06/05/12 10:30 AM
Joined: Jun 2001
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South Carolina
Jake Offline
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you could park a car on it...but, lets say you had a mild level of vacuum at 20 inches of mercury (-9.8psi) on a daggerboard that measures 60 inches by 10 inches, you will need to park 5,880 lbs on it and somehow get that pressure evenly distributed on the layup.


Jake Kohl
Re: vacuum bag [Re: pgp] #249237
06/05/12 11:59 AM
06/05/12 11:59 AM
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pgp Offline OP
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Ah, enlightenment...


Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: vacuum bag [Re: pgp] #249243
06/05/12 12:15 PM
06/05/12 12:15 PM
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Naples, FL
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Originally Posted by pgp
So which is the superior method for home building dagger boards, rudders and other relatively "flat" panels, vacuum or pressure?



Dude, just go with explosive bonding and be done with it. You could have an aluminum/nobium boards in no time...


Jay

Re: vacuum bag [Re: pgp] #249246
06/05/12 12:42 PM
06/05/12 12:42 PM
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pgp Offline OP
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...there's one in every crowd.

http://www.youtube.com/watch?v=QDNX...ad=5295696183&kw=explosive%20bonding

My Blade could handle that, no pro'lem

Last edited by pgp; 06/05/12 12:45 PM.

Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: vacuum bag [Re: pgp] #249268
06/06/12 03:56 AM
06/06/12 03:56 AM
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waynemarlow Offline
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Pete, if you don't want noise and do not require lots of air evacuation, try a water venturi vacumn pump, you probably remember them in the school lab, cheap simple, use a surprising little amount of water and can pull a surprising amount of vacumn. The thing they cannot do is evacuate huge amounts of air quickly like a mechanical pump. We used to use them for calibrating aircraft instruments and 50000ft was pretty achievable in a round glass goldfish bowl with a 10mm ali plate lid. A 10K dollar rig for about $ 100.00

Re: vacuum bag [Re: pgp] #249270
06/06/12 06:27 AM
06/06/12 06:27 AM
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pgp Offline OP
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http://www.youtube.com/watch?v=VodfQcrXpxc&feature=related

I've no experience with that but I've quite a bit of experience with this: http://www.youtube.com/watch?v=SDprRTHw4I0

Use a stethoscope to find small leaks.

To do it right, I guess you really need the proper equipment.

Last edited by pgp; 06/06/12 06:31 AM.

Pete Pollard
Blade 702

'When you have a lot of things to do, it's best to get your nap out of the way first.

Re: vacuum bag [Re: pgp] #249272
06/06/12 06:37 AM
06/06/12 06:37 AM
Joined: Oct 2002
Posts: 1,226
Atlanta
bvining Offline
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You could always rent a compressor if you didnt want to buy one.

www.unitedrentals.com

Plus this kit, (which you need anyway) and you have a tried and true system for making composite parts.

http://www.jamestowndistributors.co...amilyName=WEST+System+Vacuum+Bagging+Kit


Re: vacuum bag [Re: pgp] #249443
06/11/12 03:08 PM
06/11/12 03:08 PM
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Palm Beach County
TheManShed Offline
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Pete what are you trying to build?


Mike Shappell
www.themanshed.com
TMS-20 Builder
G-Cat 5.7 - Current Boat
NACRA 5.2 - early 70's

Re: vacuum bag [Re: pgp] #249548
06/14/12 04:29 AM
06/14/12 04:29 AM
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phill Offline
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Originally Posted by pgp
I'm not buying any more gadgets to get used once, then gather dust for decades.

Besides, I'm obsessed with the question...


Pete,
You can make a vacuum pump from on an compressor from a cars air conditioner and an electric motor that delivers around 500 revs per minute. A couple of pulleys and a belt can get that for you.
Trust me you will use it a lot more than once.
I had a friend who wanted to laminate some timber to make a gun stock. I'm not into guns at all but offered him some advice. I told him to work out the area of the wood and the pressure he could get under vacuum (around 14 psi) and just get bricks and stack them on top of his wood. That way he would get good pressure without a vacuum. On the way home I did some mental calculations and worked out the stack of bricks would need to be nearly 28feet high (8.5m) just to get the pressure he could get with a simple vacuum.

As a side note when vacuuming my F85SR floats I worked out I would need 53 tons of weight evenly distributed to apply the same amount of pressure as a simple vacuum pump. I am now working with 3 different vacuum pumps depending on the job I'm working on with a Milking machine in the wings to turn into a vacuum pump should I get the time. Even with the simple process of glueing two bits of ply together. Do it under a vacuum and you won't be able to see what is your glue joint and what is the production ply glue joint.

Think about it a little and see how it falls.

Regards,
Phill

Last edited by phill; 06/14/12 04:31 AM.

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!

Re: vacuum bag [Re: phill] #249549
06/14/12 05:52 AM
06/14/12 05:52 AM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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There are a lot of economical vacuum pumps available now for around $100 US that are good for building composites (but maybe not for HVAC work).


Jake Kohl
Re: vacuum bag [Re: Jake] #249551
06/14/12 06:57 AM
06/14/12 06:57 AM
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West coast of Norway
Rolf_Nilsen Offline
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Originally Posted by Jake
There are a lot of economical vacuum pumps available now for around $100 US that are good for building composites (but maybe not for HVAC work).


Links? Ebay? smile

Re: vacuum bag [Re: Rolf_Nilsen] #249552
06/14/12 07:34 AM
06/14/12 07:34 AM
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Posts: 778
Houston
carlbohannon Offline
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Originally Posted by Rolf_Nilsen
Originally Posted by Jake
There are a lot of economical vacuum pumps available now for around $100 US that are good for building composites (but maybe not for HVAC work).


Links? Ebay? smile


try:
http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=gast+vacuum+pump&_sacat=0

Gast is a common industrial brand in North America. There are others.

I bought a oil less rotary vane pump with tanks, manifold, gauge, and pressure controller for ~$100 10 years ago. I see several similar units in the link.

Suggestion, use a filter. Many of the small units have a short life without them. I use a jar with paper towel media backed up with an inline water filter.

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