vacumm bagging, another approach?

To get one atmosphere of pressure you have to go down 33 feet. A backyard pool with a depth of 6 feet gives less than 3psi. 12 feet gives about 5.5psi.

It might add a little extra squeeze, but not much.

Lemme guesss.... you scuba?

Ted Novak TRA#5512 IEAS#75

Yup. Recertified after 20+ years and planning a trip to the Florida Keys with my son's Boy Scout troop. There's no such thing as too many hobbies, is there? ;-)

I certified in '82 on Maui. Haven't dived, or gone back since '85 but my sis still scubas when she goes down to FL.

When people ask me about the scuba experience I just tell them it's damn near religious. Something about swimming with sharks and not getting eaten :)

Ted Novak TRA#5512 IEAS#75

The pool should work if you don't crush the tubes.

would i be correct then to say that dropping down to 33 feet will be the equivalent of pulling full vacuum then?

ok, so a pool wont do it......but the laze at one of our launch sites would do. wazee lake, 355 feet. wonder what kind of rube goldberg device i'd have to build for that?

Why? More pressure is not better. In fact, you can overdo it and end up with a structure that doesnt have enough resin just using a good vacuum pump.

i was hpoing someone would bring that up. wonder how you could counteract that.......maybe an excess resin to meet the volume of the excess resivoir. need to have a floatign check valve then.

rube goldberg indeed.

note: planning on something big, so buying a vacuum pump may be prohibitive, renting non-realistic.

maybe using a gas engine driven by an electric motor. hmmmm

I've done 5.5" tubes using a Foodsaver vacuum sealer.

I've also had very good luck with release + breather only (no vacuum).

The benefit of vacuum is that it removes more resin which means it saves weight. There is no benefit in the strength of the composite. I did a quick estimate once on how much weight I could save on a large rocket (say 25lbs dry) using vacuum (2:1 fabric:resin) vs not (1:1). IIRC, less than a pound (assuming 3 wraps of 5oz cloth). Made me wonder why I even bother. On smaller/lighter rockets the weight savings may be worth the effort.

I th> i was hpoing someone would bring that up. wonder how you could counteract

Why not just use heat shrink tape, aerosleeve glass and a heat gun?

Ted Novak TRA#5512 IEAS#75

You're starting to sound like you are serious about this. If you are you should do your homework before you jump in. 8-)

Why not put it into a bucket of wet concrete???? The extra density of the concrete should work wonders. Besides, when the concrete cures your part is sure to never come appart!!!

KT

There is an optimum ratio of fabric to resin which is 60:40 (fabric to resin) for most of the stuff we are likely to use. This is pretty dry looking. If you get too much resin on the part, it can clog the breather, ooze down the vacuum line, and into the pump. I've never gotten farther than into the first few inches of vacuum line, but I tend to use a long line now to ensure that it never makes it to the pump.

Larry

Alex Mericas wrote:

You dont need a big pump to do a big project, unless we're talking about something on the scale of a boat hull.

Assuming we're talking about rockets, any vacuum pump will do. It doesnt take much CFM to do vacuum bagging. In fact, I often use a vacuum cleaner to get most of the air out of the bag first, then switch to the vacuum pump.

If you've got a compressor you can use one of those venturi vacuum generators.

prohibitive,

yes i am

i've heard that aricraft builders don't even use the vacuum pump in this method. but you do need to use a vacuum that uses and extra fan to cool the motor as most use the vacuum impeller for double duty

I didn't know you were a lawyer.

No but I do work for them. Just started a new gig at a firm today :)

Ted Novak TRA#5512 IEAS#75

He didn't say He *was* a shark.

Do You keep the spear gun handy?