Vaccuumm Bagging

[mlefebvre]

Is anyone using vaccuumm bagging techniques in your epoxy layups? I figure this is a great way to get deeper total coverage and less weight. What are your thoughts on that?

 

Marc

[LargePrime]

http://cozyaircraft.com/forum/showthread.php?threadid=523&highlight=epoxy+weight

 

towards the bottom

[dust]

Most of what you build cannot be bagged and what you can bag would be very dificult to do, except for the bulkheads

 

bulkheads, easy to bag, 2% of the glass

 

fuselodge inside, because of the forms the inside sides and bottom are sitting on to hold there shape, it seems as though it would be very, very dificult to bag as all of the forms are screwed to the work bench and many many sharp edges to have to round over.

 

fuselodge outside, the fuselodge is on a rotiseri and is big and hollow, can't imigine trying to bag it.

 

Wings - canard i guess if you really jumped through some hoops you could bag this part, but the process would be very dificult, i think the bag would introduce preasures to deform wing, the canard is cut apart for the sheer web, then glued back together for the spar caps.

 

Main wings - same as above but ten times worse

 

Many many layups are reinforcements. no way to bag them.

 

 

The way we work is

 

Do as good a job in the layup procedure and use a little heat from a hair dryer to get the epoxy to flow better, keep the hardener and resin in a heated cabinet.

 

Lay up almost all reinforcements on the bench where it is easy to do a good job of squeegeing out excess epoxy and then placing the reinforcement into position and removing the plastic butcher paper.

 

When we did our test layup years ago, the weight(from memory) allowable on the piece was from 9 to 11 oz, ours was 9.1

 

less than 9 and not enough epoxy, more than 11 obviously - way too much.

 

Remember, a little heat to thin out epoxy, a little time for it to move into position, a little excess on lower layers, the cloth likes to suck up extra from below and you will have a fine layup

 

enjoy the build

 

Mike

[John Slade]

I think Dust's right about vacuum bagging, although I think some have done it.

 

An excellent compromise is the "poor mans vacuum bagging" or "plastic peel ply" approach, where you use 4ml plastic on top of the layup to squeege out the bubbles and compress the fibers. This gets rid of pinholes and gives you a very light part that's easy to sand for bond without damaging the fibers. In some cases I use cloth peel ply under the plastic. I've described the technique in detail in my web site see http://kgarden.com/cozy/tips.htm

 

I know a lot of people steer clear of this approach for some reason. I swear by it, and rarely do a layup without plastic.

[Jim Sower]

I've been putzing around with vacuum-bagging for years, and talking to lots of folks - guys who have done it extensively and invented/developed many of the techniques in use today. The almost unanimous concensus: a) it's a great thing - the only way to go - for making moulded parts; b) it's waaaaaay more trouble than it's worth for hand laid up structures like Cozy, EZ.

 

I've tried John's "plastic-bagging" and have become a true believer. It is PARTICULARLY effective when you use a very low viscosity epoxy (like the hi-$ MGS 285) and keep it hot and flowing like water.

 

The difference in quality and weight between plastic-bagging with low viscosity epoxy and vacuum-bagging has to be trivial and would no way justify the extra effort of vacuum-bagging.

 

Additionally, I have found that wnen vacuum-bagging a flat surface (like a bulkhead or fuselage side), the pressure seems to cause the bag to press the glass down into the foam in some places [and not / more than] in others making a more wavy surface than would be the case with plastic-bagging. I tend to believe that foam is like that. Even the factories always bag the INSIDE of a surface and keep the outside next to the mould so that the waviness is harder to detect and much less of a problem.

 

I'm with John S. and Dust on this one .... Jim S.

[Spodman]

Hello John Slade,

 

I've read your site extensively and like the look of your plastic ply technique, but what exactly is the "4ml plastic". I guess it isn't 4 millimeter:confused:

[John Slade]

>I guess it isn't 4 millimeter

It's the clear plastic sheeting available at Home Depot paint dept. I think the abreviation is 4ML standing for 4 millimeter.

[filipo]

mil stands for a thousandth of an inch.

mm is the proper symbol for millimeter (aka millimetre).

 

Why can't we all just get along and live in a metric world...?

[Spodman]

Thanks all, that makes more sense. My main gripe about the design of the Cozy (and lots of neat things I see to make in Popular Mechanics, etc.) is the crazy, old-fashioned Imperial measurements. I don't own any measuring devices with feet/inches/cubits/fathoms on 'em or any but metric tools; and would like to keep it that way.

 

After a bit more reading of all the wonderful websites of Cozy builders out there I've now grasped that Nat has drawn up the Cozy in a sort of hybrid metric system based on the inch. I suppose I could let such a tape measure into my life, seing he's met me half way:)

[chuckthedog]

I worked in a repair shop for around 30 years, and have seen metric and it aint pirty when you have to stock the taps, dies, bolt, and nuts. There are around 5 to 10 thread pitches for each diameter nut and bolt. The French wont use any pitch the rest of the world uses. The Japs won,t use English. Etc etc. Don't get me wrong metric in theory is good. In the real world it has a long way to go to get everyones fingers on the same page. Get it, fingers, 10.

HAPPY NEW YEAR